MPR Met-Pro Corp.

NOTICE OF SPECIAL MEETING OF STOCKHOLDERS

TO BE HELD AUGUST 26 , 2013

To Our Stockholders:

A special meeting of stockholders of CECO Environmental Corp. (“CECO”) will be held at its executive offices, 4625 Red Bank Road, Suite 200, Cincinnati, Ohio 45227 on August 26, 2013 at 11:30 a.m, Eastern Time. The special meeting of stockholders is being held for the following purposes:

1. To approve the issuance of CECO common stock to Met-Pro Corporation (“Met-Pro”) shareholders in the First Merger contemplated by the Agreement and Plan of Merger, dated as of April 21, 2013 (the “Merger Agreement”), by and among CECO, Met-Pro, Mustang Acquisition Inc., a wholly-owned subsidiary of CECO (“Merger Sub”), and Mustang Acquisition II Inc., a separate wholly-owned subsidiary of CECO (Mustang Acquisition II Inc., or its successor limited liability company, “Merger Sub II”), a copy of which is attached as Annex A to the accompanying joint proxy statement/prospectus, pursuant to which (i) Merger Sub will merge with and into Met-Pro (the “First Merger”) and (ii) Met-Pro will merge with and into Merger Sub II (CECO Proposal No. 1);

2. To approve an amendment to CECO’s 2007 Equity Incentive Plan to increase the number of shares of common stock available for issuance thereunder from 2,000,000 to 2,600,000, as set forth in the CECO Amended and Restated 2007 Equity Incentive Plan, a copy of which is attached as Annex D to the accompanying joint proxy statement/prospectus (CECO Proposal No. 2); and

3. To approve the adjournment or postponement of the special meeting, if necessary or appropriate, for, among other reasons, the solicitation of additional proxies in the event that there are not sufficient votes at the time of the special meeting to approve CECO Proposal Nos. 1 and 2 (CECO Proposal No. 3).

Only stockholders of record at the close of business on July 19, 2013 are entitled to vote at the special meeting or at any adjournment or postponement thereof.

We hope that as many stockholders as possible will personally attend the special meeting. Whether or not you plan to attend the meeting, please complete the enclosed proxy card and sign, date and return it promptly so that your shares will be represented. You also may vote your shares by telephone or through the Internet by following the instructions set forth on the proxy card.

The board of directors of CECO unanimously recommends that you vote “FOR” each of (i) the issuance of CECO common stock to Met-Pro shareholders in the First Merger, (ii) the amendment to CECO’s 2007 Equity Incentive Plan to increase the number of shares of common stock available for issuance thereunder from 2,000,000 to 2,600,000 and (iii) the adjournment or postponement of the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

July 25, 2013

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MET-PRO CORPORATION

NOTICE OF SPECIAL MEETING OF SHAREHOLDERS

TO BE HELD AUGUST 26, 2013

To Our Shareholders:

A special meeting of shareholders of Met-Pro Corporation (“Met-Pro”) will be held at The Holiday Inn Lansdale, 1750 Sumneytown Pike, Kulpsville, Pennsylvania 19443 on August 26, 2013 at 11:00 A.M., Eastern Time. The special meeting of shareholders is being held for the following purposes:

1. To adopt the Agreement and Plan of Merger, dated as of April 21, 2013 (the “Merger Agreement”), by and among CECO Environmental Corp. (“CECO”), Met-Pro, Mustang Acquisition Inc., a wholly-owned subsidiary of CECO (“Merger Sub”), and Mustang Acquisition II Inc., a separate wholly-owned subsidiary of CECO (Mustang Acquisition II Inc., or its successor limited liability company, “Merger Sub II”), a copy of which is attached as Annex A to the accompanying joint proxy statement/prospectus, pursuant to which (i) Merger Sub will merge with and into Met-Pro (the “First Merger”) and (ii) Met-Pro will merge with and into Merger Sub II (the “Second Merger” and together with the First Merger, the “Mergers”), and approve the transactions contemplated by the Merger Agreement, including the First Merger (Met-Pro Proposal No. 1);

2. To approve, by non-binding advisory vote, the merger-related compensation that may become payable to Met-Pro’s named executive officers in connection with the Mergers (Met-Pro Proposal No. 2); and

3. To approve the adjournment or postponement of the special meeting, if necessary or appropriate, for, among other reasons, the solicitation of additional proxies in the event that there are not sufficient votes at the time of the special meeting to approve Met-Pro Proposal Nos. 1 and 2 (Met-Pro Proposal No. 3).

Only shareholders of record at the close of business on July 19, 2013 are entitled to vote at the special meeting or at any adjournment or postponement thereof.

Whether or not you plan to attend the special meeting, please complete the enclosed proxy card and sign, date and return it promptly so that your shares will be represented. You also may vote your shares by telephone or through the Internet by following the instructions set forth on the proxy card. Submitting your proxy in writing, by telephone or through the Internet will not prevent you from voting in person at the special meeting.

The board of directors of Met-Pro, by unanimous vote, has determined that it is in the best interests of Met-Pro and its shareholders to consummate the transactions contemplated by the Merger Agreement, and unanimously recommends that you vote “FOR” each of (i) the adoption of the Merger Agreement and approval of the transactions contemplated thereby, including the First Merger, (ii) the approval, by non-binding advisory vote, of the merger-related compensation that may become payable to Met-Pro’s named executive officers in connection with the Mergers and (iii) the adjournment or postponement of the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

SHAREHOLDERS WHO CANNOT ATTEND IN PERSON ARE REQUESTED TO VOTE

AS PROMPTLY AS POSSIBLE

July 25, 2013

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QUESTIONS AND ANSWERS ABOUT THE MERGERS

AND THE MET-PRO SPECIAL MEETING

The following questions and answers address briefly some questions you may have regarding the Mergers and the Met-Pro special meeting. These questions and answers may not address all questions that may be important to you as a shareholder of Met-Pro or as a stockholder of CECO. Please refer to the more detailed information contained elsewhere in this joint proxy statement/prospectus, the annexes to this joint proxy statement/prospectus and the documents referred to in or incorporated by reference into this joint proxy statement/prospectus. You may obtain the information incorporated by reference into this joint proxy statement/prospectus without charge by following the instructions in the section entitled “Where You Can Find More Information” beginning on page 179.

For certain questions and answers about the CECO special meeting, see the section entitled “Questions and Answers about the CECO Special Meeting” beginning on page 9.

What are the Mergers?

In accordance with the terms and conditions of the Merger Agreement, if Met-Pro shareholders adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, and CECO stockholders approve the issuance of CECO common stock to Met-Pro shareholders in the First Merger, and the other closing conditions in the Merger Agreement are satisfied or waived, (i) Merger Sub will merge with and into Met-Pro and (ii) Met-Pro will merge with and into Merger Sub II. As a result of the Mergers, the separate corporate existence of Met-Pro will cease, and the wholly-owned subsidiary of CECO will continue as the surviving company and a wholly-owned subsidiary of CECO. A copy of the Merger Agreement is attached as Annex A to this joint proxy statement/prospectus.

Is my vote necessary to complete the Mergers?

Yes. The companies have agreed to combine the two companies upon the terms and conditions of the Merger Agreement that is described in this joint proxy statement/prospectus. You are receiving these proxy materials to help you decide, among other matters, how to vote your shares of Met-Pro with respect to the proposed Mergers.

The Mergers cannot be completed unless, among other things, Met-Pro shareholders adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger.

The Met-Pro special meeting is being held to vote on, among other matters, the proposals necessary to complete the Mergers. Information about this meeting, the Mergers and the other business to be considered by Met-Pro shareholders is contained in this joint proxy statement/prospectus.

Your vote is important. Met-Pro encourages you to vote as soon as possible.

Are there other matters related to the Mergers that require the vote of Met-Pro shareholders?

Yes. At the Met-Pro special meeting, shareholders will be asked to consider and vote upon a proposal to approve, by non-binding advisory vote, the agreements and understandings of Met-Pro and its named executive officers concerning compensation that may become payable to or on behalf of such executive officers which is based on or otherwise relates to the Mergers, and the aggregate total of all such compensation. These payments are disclosed in this joint proxy statement/prospectus in the section entitled “The Mergers—Interests of Met-Pro Directors and Executive Officers in the Mergers—Merger-Related Compensation” beginning on page 83 and the section entitled “Met-Pro Proposal No. 2: Approval, by Non-Binding Advisory Vote, of the Merger-Related Payments That May Become Payable to Its Named Executive Officers” beginning on page 163.

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What will shareholders receive in the Mergers?

Met-Pro shareholders may make one of the following elections, or a combination of the two, regarding the type of Merger Consideration they wish to receive in exchange for shares of Met-Pro common stock:

If Met-Pro shareholders make a cash election or a stock election, the form of Merger Consideration that they actually receive as a Met-Pro shareholder may be adjusted as a result of the proration procedures contained in the Merger Agreement and described in this joint proxy statement/prospectus in the section entitled “The Mergers—Met-Pro Shareholders Making Cash and Stock Elections” beginning on page 90. These proration procedures are designed to ensure that approximately 53% of the Met-Pro shares (treating all Equity Award Shares as outstanding shares) will be exchanged for cash (which, together with the amount of cash paid for Equity Award Shares, is capped at $109.5 million) and approximately 47% of the Met-Pro shares outstanding immediately prior to the First Merger are converted into the right to receive CECO common stock.

For more information regarding the consideration Met-Pro shareholders may receive in connection with the First Merger, see the section entitled “The Mergers—Merger Consideration” beginning on page 87.

How and when do Met-Pro shareholders make a cash election or a stock election?

Met-Pro shareholders should carefully review and follow the instructions accompanying the form of election, which will be mailed to you separately from this joint proxy statement/prospectus within five business days after the mailing of this joint proxy statement/prospectus. Met-Pro shareholders of record as of July 19, 2013 will have a minimum of 14 business days following the mailing date of the form of election to make their elections. Any Met-Pro shareholder who became a Met-Pro shareholder after the record date for the special meeting, or who did not otherwise receive a form of election, should contact Met-Pro or his, her or its broker, bank or other nominee to obtain a form of election. Met-Pro will make available forms of election to such persons up until the close of business on the last business day prior to the election deadline. To make a cash election or a stock election, Met-Pro shareholders of record must properly complete, sign and send the form of election and any stock certificates representing their Met-Pro shares, or a guarantee of delivery as described in the instructions accompanying the form of election, to American Stock Transfer & Trust Company, LLC, the exchange agent, as follows:

The exchange agent must receive the form of election and any stock certificates representing Met-Pro shares, or a guarantee of delivery as described in the instructions accompanying the form of election, at or prior to the election deadline. The election deadline will be 5:00 p.m., Eastern Time, on the date that is one business day before the date of the Met-Pro special meeting (or such other date as CECO and Met-Pro mutually agree). CECO and Met-Pro will publicly announce the anticipated election deadline at least five business days prior to the date of the Met-Pro special meeting.

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If you own Met-Pro shares in “street name” through a bank, broker or other nominee and you wish to make an election, you should follow the instructions in the form of election that will be sent to you shortly after the mailing of this proxy statement, and you may also seek assistance from the financial institution holding your shares, as to the completion of the form of election.

If you own Met-Pro shares through Met-Pro’s 401(k) plan or through the Met-Pro ESOP, you should follow the instructions in the form of election that will be sent to you shortly after the mailing of this proxy statement as to the completion of the form of election.

Regardless of the manner in which you own your Met-Pro shares, you may also call Morrow & Co., LLC, Met-Pro’s proxy solicitation firm, for assistance in connection with the completion of the form of election. Morrow’s telephone number is (800) 662-5200, and its email address is metproinfo@morrow.com. This information is also found in the form of election.

Can Met-Pro shareholders elect to receive cash consideration for a portion of Met-Pro shares and stock consideration for remaining Met-Pro shares?

Yes. The form of election allows an election to be made for cash consideration for a portion of Met-Pro shares and stock consideration for remaining Met-Pro shares.

Can Met-Pro shareholders change their election after the form of election has been submitted?

Yes. Met-Pro shareholders may revoke an election at or prior to the election deadline by submitting a written notice of revocation to the exchange agent at or prior to the election deadline. Revocations must specify the name in which the shares are registered on the share transfer books of Met-Pro and such other information as the exchange agent may request. If Met-Pro shareholders wish to submit a new election, they must do so at or prior to the election deadline in accordance with the election procedures described in this joint proxy statement/prospectus and the form of election, which will be mailed to you separately from this joint proxy statement/prospectus no later than five business days after the mailing of this joint proxy statement/prospectus. If Met-Pro shareholders instructed a broker or other nominee holder to submit an election for their shares, they must follow the broker’s or other nominee’s directions for changing those instructions. The notice of revocation must be received by the exchange agent at or prior to the election deadline in order for the revocation to be valid.

May Met-Pro shareholders transfer Met-Pro shares after making a cash election or a stock election?

No. Once a Met-Pro shareholder properly makes an election with respect to any shares of Met-Pro common stock, they will be unable to sell or otherwise transfer those shares, unless they properly revoke their election at or prior to the election deadline or unless the Merger Agreement is terminated.

What happens if a Met-Pro shareholder does not send a form of election or it is not received by the election deadline?

If the exchange agent does not receive a properly completed form of election from a Met-Pro shareholder at or prior to the election deadline (together with any stock certificates representing the shares of Met-Pro common stock covered by the election or a guarantee of delivery as described in the form of election), then such Met-Pro shareholder will be deemed not to have made an election and will have no control over the type of Merger Consideration they receive. As a result, Met-Pro shares may be exchanged for cash consideration, stock consideration or a combination of cash consideration and stock consideration in accordance with the proration procedures contained in the Merger Agreement and described in the section entitled “The Mergers—Met-Pro Shareholders Making Cash and Stock Elections” beginning on page 90. Met-Pro shareholders bear the risk of delivery of all the materials that they are required to submit to the exchange agent in order to properly make an election.

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If a Met-Pro shareholder does not properly make an election with respect to all Met-Pro shares they owned of record, after the completion of the First Merger they will receive written instructions from the exchange agent on how to exchange Met-Pro stock certificates for the shares of CECO common stock and/or cash that they are entitled to receive in the First Merger as a non-electing Met-Pro shareholder.

Because Met-Pro shareholders making elections will likely take the relative values of the stock consideration and cash consideration into account in determining what form of election to make, they will likely elect the form of consideration resulting in the higher value. As a result, if a Met-Pro shareholder fails to make an election they are likely to receive the consideration having the lower value (based on the relative values of the cash consideration and the stock consideration as of the last trading day before the closing of the First Merger).

May Met-Pro shareholders submit a form of election even if they do not vote to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger?

Yes. Met-Pro shareholders may submit a form of election even if they fail to vote, abstain, or vote against the adoption of the Merger Agreement and approval of the transactions contemplated thereby, including the First Merger.

Where and when is the special meeting of Met-Pro shareholders?

The special meeting will be held on August 26, 2013 at 11:00 A.M., Eastern Time at The Holiday Inn Lansdale, 1750 Sumneytown Pike, Kulpsville, Pennsylvania 19443.

Who can vote at the Met-Pro special meeting?

Met-Pro shareholders can vote at the Met-Pro special meeting if they owned shares of Met-Pro common stock at the close of business on July 19, 2013, the record date for the special meeting.

Who can attend the Met-Pro special meeting?

All shareholders of record as of July 19, 2013, or their duly appointed proxies, may attend the meeting. Cameras, recording devices and other electronic devices will not be permitted at the meeting. If you hold your shares in “street name,” you will need to bring a copy of a brokerage statement reflecting your stock ownership as of the record date.

What vote of Met-Pro shareholders is required to approve the proposals?

To adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, holders of a majority of the outstanding shares of Met-Pro common stock entitled to vote must vote their shares “FOR” the proposal. As a result, abstentions and failures to vote have the effect of a vote “AGAINST” the proposal to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger.

To approve, by non-binding advisory vote, the merger-related compensation, holders of a majority of the shares of Met-Pro common stock casting votes at the special meeting must vote their shares “FOR” the proposal. As a result, abstentions and failures to vote will have no effect on the proposal to approve, by non-binding advisory vote, the merger-related compensation.

To approve adjournment or postponement of the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies, holders of a majority of the shares of Met-Pro common stock casting votes at the special meeting must vote their shares “FOR” the proposal. As a result, abstentions and failures to vote will have no effect on the proposal to adjourn or postpone the special meeting.

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What constitutes a quorum for the Met-Pro special meeting?

A majority of the outstanding shares of Met-Pro’s common stock entitled to vote being present in person or represented by proxy constitutes a quorum for the special meeting. If a quorum is not present, the shareholders present, in person or by proxy, may adjourn the meeting, without notice other than announced at the meeting, to another place, if any, date or time.

How does the Board of Directors of Met-Pro recommend that Met-Pro shareholders vote?

The Met-Pro board of directors, by unanimous vote, has determined that the Merger Agreement and the transactions contemplated thereby are in the best interests of Met-Pro and its shareholders and recommends that Met-Pro shareholders vote:

The board is soliciting shareholder votes consistent with the board’s recommendation.

You should read the section entitled “The Mergers—Met-Pro’s Reasons for the Mergers and Recommendation of Met-Pro Board of Directors” beginning on page 57 for a discussion of the factors that the board considered in deciding to recommend voting “FOR” the adoption of the Merger Agreement and approval of the transactions contemplated thereby, including the First Merger.

How do I vote?

If you are a Met-Pro shareholder of record (or if you hold any shares in the Met-Pro ESOP) after carefully reading and considering the information contained in this joint proxy statement/prospectus you may vote by any of the following methods:

Met-Pro recommends that you vote in advance even if you plan to attend the meeting so that Met-Pro will know as soon as possible that enough votes will be present for Met-Pro to hold the meeting. If you are a shareholder of record and attend the meeting, you may vote at the meeting or deliver your completed proxy card in person.

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If you are a shareholder of record and if you properly return or submit your proxy but do not indicate how you wish to vote, Met-Pro will count your proxy as a vote “ FOR ” the adoption of the Merger Agreement and approval of the transactions contemplated thereby, including the First Merger, “ FOR ” the approval, by non-binding advisory vote, of the merger-related compensation and “ FOR ” adjournment or postponement of the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

If you hold any shares in the Met-Pro ESOP and you properly return or submit your proxy but do not indicate how you wish to vote, such shares will not be voted by the ESOP trustee and will have the effect of a vote “AGAINST” the proposal to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, and will have no effect on the proposal to approve, by non-binding advisory vote, the merger-related compensation and the proposal to adjourn or postpone the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

If your shares are held in “street name,” please refer to the information forwarded to you by your bank, broker or other holder of record to see what you must do in order to vote your shares, including whether you may be able to vote electronically through your bank, broker or other record holder. If so, instructions regarding electronic voting will be provided by the bank, broker or other holder of record to you as part of the package that includes this joint proxy statement/prospectus. If you are a “street name” stockholder and you wish to vote in person at the meeting, you will need to obtain a proxy from the institution that holds your shares and present it to the inspector of elections with your ballot when you vote at the special meeting.

What is the difference between a shareholder of record and a “street name” beneficial holder of shares?

If your shares are registered directly in your name with Met-Pro’s transfer agent, American Stock Transfer & Trust Company, LLC, you are considered a shareholder of record with respect to those shares. If this is the case, the shareholder proxy materials have been sent or provided directly to you by Met-Pro.

If your shares are held in a stock brokerage account or by a bank or other nominee, you are considered the “beneficial holder” of the shares held for you in what is known as “street name.” If this is the case, the proxy materials have been forwarded to you by your brokerage firm, bank or other nominee, which is considered the shareholder of record with respect to these shares. As the beneficial holder, you have the right to direct your broker, bank or other nominee how to vote your shares. Please contact your broker, bank, or other nominee for instructions on how to vote any shares you beneficially own.

If my shares are held in “street name” by my broker, will my broker vote my shares for me?

No. If your shares are held for you as a beneficial owner in “street name,” your broker will vote your shares on the proposals only if you provide instructions to your broker on how to vote. You should follow the directions provided by your broker regarding how to instruct your broker to vote your shares. Without instructions, your shares will not be voted and will have the effect of a vote “AGAINST” the proposal to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, and will have no effect on the proposal to approve, by non-binding advisory vote, the merger-related compensation and the proposal to adjourn or postpone the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

Can I change my vote after I have delivered my proxy?

Yes. You can change your vote before the Met-Pro special meeting. If you are a Met-Pro shareholder of record (or if you hold any shares in the Met-Pro ESOP), you may change your proxy voting instructions prior to commencement of the special meeting by:

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If your shares are held in “street name,” you may change your vote by submitting new voting instructions to your broker or other nominee holder in accordance with the procedures established by it. Please contact your broker or other nominee and follow its directions in order to change your vote.

What if I do not specify a choice for a matter when returning a proxy?

Shareholders should specify their choice for each matter on the enclosed proxy.

If you are a shareholder of record and no specific instructions are given, proxies that are signed and returned will be voted:

If your shares are held in the Met-Pro ESOP or in “street name” and no specific instructions are given, then such shares will not be voted and will have the effect of a vote “AGAINST” the proposal to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, and will have no effect on the proposal to approve, by non-binding advisory vote, the merger-related compensation and the proposal to adjourn or postpone the special meeting, if necessary or appropriate, to, among other reasons, solicit additional proxies.

The board is soliciting shareholder votes consistent with the board’s recommendation.

Should I send in my Met-Pro stock certificates with my proxy card?

No. Please DO NOT send your Met-Pro stock certificates with your proxy card.

Should I send in my form of election with my proxy card?

No. If you wish to make an election with respect to your Met-Pro shares, then, prior to 5:00 p.m., Eastern Time, on the last business day prior to the Met-Pro special meeting, American Stock Transfer & Trust Company, LLC, the exchange agent, must have received your completed, signed form of election (together with your Met-Pro stock certificates or a guarantee of delivery) as described in the form of election. This form of election will be mailed to you separately from these proxy materials within five business days after the mailing of these proxy materials.

If your shares are held in “street name,” you should follow the instructions in the form of election that will be sent to you shortly after the mailing of this joint proxy statement/prospectus, and you may also seek assistance from the financial institution holding your shares, as to the completion of the form of election.

If you own Met-Pro shares through Met-Pro’s 401(k) plan or through the Met-Pro ESOP, you should follow the instructions in the form of election that will be sent to you shortly after the mailing of this joint proxy statement/prospectus as to the completion of the form of election.

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Regardless of the manner in which you own your Met-Pro shares, you may also call Morrow & Co., LLC, Met-Pro’s proxy solicitation firm, for assistance in connection with the completion of the form of election. Morrow’s telephone number is (800) 662-5200, and its email address is metproinfo@morrow.com. This information is also found in the form of election.

If you make no election with respect to your Met-Pro shares, after the completion of the First Merger you will receive a letter of transmittal for you to use in surrendering any Met-Pro stock certificates you have at that time.

When do Met-Pro and CECO expect the Mergers to be completed?

Met-Pro and CECO are working to complete the Mergers as quickly as possible. If the Merger Agreement is adopted and the transactions contemplated thereby, including the First Merger, are approved by Met-Pro shareholders, the issuance of CECO common stock to Met-Pro shareholders in the First Merger is approved by CECO stockholders, and the other conditions to completion of the Mergers are satisfied or waived, it is anticipated that the Mergers will be completed in the third quarter of 2013.

Will Met-Pro continue to pay dividends on its common stock until the Mergers are completed?

Under the terms of the Merger Agreement, Met-Pro is expressly permitted to continue to pay a quarterly dividend of $0.0725 per share consistent with its past practice; provided, however, that as previously announced, in the event that the closing of the First Merger occurs before August 30, 2013, then the Met-Pro dividend declared on June 5, 2013 (which has a record date of August 30, 2013) shall not be paid to Met-Pro’s shareholders, and in such event, CECO has agreed to set its record date for the payment of its third dividend occurring during its current fiscal year to occur on a date that is at least two business days after the closing of the First Merger. Additionally, all future dividend payments are at the discretion of the Met-Pro board and changes in the dividend program will depend on Met-Pro’s earnings, capital requirements, financial condition, debt covenants and other factors considered relevant by the Met-Pro board of directors.

Can Met-Pro shareholders dissent or require appraisal of their shares?

No. Under Pennsylvania law, Met-Pro shareholders do not have a right to dissent or seek an appraisal of their shares.

Who can help answer my questions?

If Met-Pro shareholders have any questions about the Mergers or the Met-Pro special meeting, or if they need additional copies of this joint proxy statement/prospectus or the enclosed proxy card or the form of election that will be sent separately from this joint proxy statement/prospectus within five business days after the mailing of this joint proxy statement/prospectus, they should contact:

Morrow & Co., LLC

470 West Avenue

Stamford, CT 06902

Call Toll Free: (800) 662-5200

Banks and Brokerage Firms Call Collect: (203) 658-9400

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QUESTIONS AND ANSWERS ABOUT THE CECO SPECIAL MEETING

The following questions and answers address briefly some questions you may have regarding the CECO special meeting. These questions and answers may not address all questions that may be important to you as a stockholder of CECO. Please refer to the more detailed information contained elsewhere in this joint proxy statement/prospectus, the annexes to this joint proxy statement/prospectus and the documents referred to in or incorporated by reference into this joint proxy statement/prospectus. You may obtain the information incorporated by reference into this joint proxy statement/prospectus without charge by following the instructions in the section entitled “Where You Can Find More Information” beginning on page 179.

For certain questions and answers about the Met-Pro special meeting and the Mergers, please refer to the section entitled “Questions and Answers about the Mergers and the Met-Pro Special Meeting” beginning on page 1.

What is the purpose of this joint proxy statement/prospectus?

The purpose of this joint proxy statement/prospectus is to provide information regarding matters to be voted on at the special meeting of CECO’s stockholders. This joint proxy statement/prospectus is also the document used by CECO’s board to solicit proxies to be used at the special meeting. Proxies are solicited by CECO’s board to give all stockholders of record an opportunity to vote on the matters to be presented at the special meeting, even if the stockholders cannot attend the meeting. The board has designated Jason DeZwirek, Jeffrey Lang and Benton Cook as proxies, who will vote the shares represented by proxies at the special meeting in the manner indicated by the proxies.

What proposals will be voted on at the CECO special meeting?

CECO stockholders will vote on the following proposals at the special meeting:

Is approval of the amendment of the Incentive Plan required to complete the Mergers?

No. However, CECO’s board of directors has made the proposed amendment of the Incentive Plan contingent upon closing of the First Merger. If the First Merger is not completed, then the proposed amendment of the Incentive Plan will not be implemented, even if approved by CECO’s stockholders.

Who is entitled to vote?

Each outstanding share of CECO’s common stock entitles its holder to cast one vote on each matter to be voted upon at the special meeting. Only stockholders of record at the close of business on the record date, July 19, 2013, are entitled to receive notice of the special meeting and to vote the shares of common stock that they held on that date at the meeting, or any adjournment or postponement of the meeting. If your shares are held for you as a beneficial holder in “street name,” please refer to the information forwarded to you by your bank, broker or other holder of record to see what you must do to vote your shares.

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A complete list of stockholders entitled to vote at the special meeting will be available for examination by any stockholder at CECO’s corporate headquarters, 4625 Red Bank Road, Suite 200, Cincinnati, Ohio 45227, during normal business hours for a period of ten days before the special meeting and at the time and place of the special meeting.

What is the difference between a stockholder of record and a beneficial holder of shares?

If your shares are registered directly in your name with CECO’s transfer agent, American Stock Transfer & Trust Company, LLC, you are considered a stockholder of record with respect to those shares. If this is the case, the stockholder proxy materials have been sent or provided directly to you by CECO.

If your shares are held in a stock brokerage account or by a bank or other nominee, you are considered the “beneficial holder” of the shares held for you in what is known as “street name.” If this is the case, the proxy materials have been forwarded to you by your brokerage firm, bank or other nominee, which is considered the stockholder of record with respect to these shares. As the beneficial holder, you have the right to direct your broker, bank or other nominee how to vote your shares. Please contact your broker, bank or other nominee for instructions on how to vote any shares you beneficially own.

Who can attend the meeting?

All stockholders of record as of July 19, 2013, or their duly appointed proxies, may attend the meeting. Cameras, recording devices and other electronic devices will not be permitted at the meeting. If you hold your shares in “street name,” you will need to bring a copy of a brokerage statement reflecting your stock ownership as of the record date.

What constitutes a quorum?

A quorum of stockholders is necessary to hold the special meeting. The presence at the meeting, in person or by proxy, of the holders of a majority of the shares of common stock outstanding on the record date will constitute a quorum. As of July 19, 2013, the record date, 17,809,334 shares of CECO’s common stock were outstanding. Abstentions and broker non-votes will be included in the calculation of the number of shares considered present at the meeting for purposes of establishing a quorum. In the event that a quorum is not present at the special meeting, CECO expects that the special meeting will be adjourned or postponed to solicit additional proxies.

How do I vote?

If you are a stockholder of record, you may vote by any of the following methods:

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CECO recommends that you vote in advance even if you plan to attend the meeting so that CECO will know as soon as possible that enough votes will be present for CECO to hold the meeting. If you are a stockholder of record and attend the meeting, you may vote at the meeting or deliver your completed proxy card in person.

If your shares are held in “street name,” please refer to the information forwarded to you by your bank, broker or other holder of record to see what you must do in order to vote your shares, including whether you may be able to vote electronically through your bank, broker or other record holder. If so, instructions regarding electronic voting will be provided by the bank, broker or other holder of record to you as part of the package that includes this joint proxy statement/prospectus. If you are a “street name” stockholder and you wish to vote in person at the meeting, you will need to obtain a proxy from the institution that holds your shares and present it to the inspector of elections with your ballot when you vote at the special meeting.

Can I change my vote after I return my proxy card?

Yes. Even after you have submitted your proxy, you may change your vote before the CECO special meeting. If you are a CECO shareholder of record, you may change your proxy voting instructions prior to commencement of the special meeting by:

If your shares are held in “street name,” you may change your vote by submitting new voting instructions to your broker, bank or other nominee holder in accordance with the procedures established by it. Please contact your broker, bank or other nominee and follow its directions in order to change your vote.

How many votes are required for the proposals to pass?

The vote required for each of (i) the approval of the issuance of CECO common stock to Met-Pro shareholders in the First Merger (CECO Proposal No. 1), (ii) the approval of the amendment of the Incentive Plan to add 600,000 shares to the total number of shares reserved for issuance under the Incentive Plan (CECO Proposal No. 2) and (iii) the proposal to adjourn or postpone the CECO special meeting, if necessary or appropriate, for, among other reasons, the solicitation of additional proxies (CECO Proposal No. 3), is the affirmative vote of a majority of the votes present, in person or by proxy, and entitled to vote on the matter.

How are abstentions and broker non-votes treated?

If a stockholder abstains from voting on CECO Proposal Nos. 1, 2 or 3, it will have the same effect as a vote “AGAINST” that proposal. Broker non-votes with respect to any matter are not entitled to vote for purposes of determining whether stockholder approval for that matter has been obtained and, therefore, have no effect on that proposal. A broker “non-vote” occurs on a proposal when shares held of record by a broker are present or represented at the meeting but the broker is not permitted to vote on that proposal without instruction from the beneficial owner of the shares and no instruction has been given. We believe that brokers, banks and other nominees do not have discretionary authority to vote on Proposal Nos. 1, 2 or 3 absent instructions from the beneficial owner and that, as a result, broker non-votes will not be entitled to vote at the CECO special meeting.

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What if I do not specify a choice for a matter when returning a proxy?

Stockholders should specify their choice for each matter on the enclosed proxy. If no specific instructions are given, proxies that are signed and returned will be voted:

What are the board’s recommendations?

The board’s recommendations, together with the description of each proposal, are set forth in this joint proxy statement/prospectus. In summary, the board recommends that you vote:

You should read the section entitled “The Mergers—CECO’s Reasons for the Mergers” beginning on page 70 for a discussion of the factors that CECO’s board considered in deciding to recommend voting “ FOR ” the approval of the issuance of CECO common stock to Met-Pro shareholders in the First Merger contemplated by the Merger Agreement.

Unless you give other instructions on your proxy card, the persons named as proxy holders on the enclosed proxy card will vote in accordance with the recommendations of the board of directors.

Who can I contact if I have any questions?

CECO Environmental Corp.

4625 Red Bank Road, Suite 200

Cincinnati, Ohio 45227

Attention: Investor Relations

Telephone: (513) 458-2600

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RISK FACTORS

In addition to the other information included in and incorporated by reference into this joint proxy statement/prospectus, Met-Pro’s shareholders should consider carefully the matters described below in determining whether to adopt the Merger Agreement and approve the transactions contemplated thereby, including the First Merger, and in determining whether to make a cash election or a stock election for each of their shares of Met-Pro common stock, and CECO’s stockholders should consider carefully the matters described below in determining whether to approve the issuance of CECO common stock to Met-Pro shareholders pursuant to the Merger Agreement and the First Merger. Please also refer to the information under the heading “Risk Factors” set forth in Part I, Item IA in each of CECO’s Annual Report on Form 10-K for the fiscal year ended December 31, 2012 and Met-Pro’s Annual Report on Form 10-K and Form 10-K/A (hereinafter the Form 10-K) for the fiscal year ended January 31, 2013, each of which is incorporated by reference into this joint proxy statement/prospectus. Please refer to the section entitled “Where You Can Find More Information” beginning on page 179.

Risk Factors Relating to the Mergers

Because the value of the CECO common stock will fluctuate, Met-Pro shareholders cannot be sure of the value of the stock they will receive in the First Merger. If you elect to receive shares of CECO common stock in the First Merger, or if you receive shares of CECO common stock in the First Merger as a result of the proration procedure set forth in the Merger Agreement, an appropriate number of shares of Met-Pro common stock you own will be automatically converted into shares of CECO common stock based upon the exchange ratio. The exchange ratio will vary between 1.0000 and 1.3520 shares of CECO common stock for each share of Met-Pro common stock and will be equal to the number determined by dividing $13.75 by the volume weighted average closing price of CECO’s common stock for the 15-trading day period ending on the last trading day before the closing of the First Merger. The net effect of this collar mechanism is that no further increase in the described exchange ratio will be made if such volume weighted average trading price is less than $10.17 and no further decrease in the exchange ratio will be made if such volume weighted average trading price is greater than $13.75. As a result, the value of the shares of CECO common stock that you will receive in the First Merger will not be known at the time you make your election as to the form of Merger Consideration or at the time you vote on the adoption of the Merger Agreement and the approval of the transactions contemplated thereby, including the First Merger, at the special meeting, and the value may go up or down as the market price of CECO common stock fluctuates, subject to the minimum and maximum exchange ratios. The specific dollar value of CECO common stock you receive upon completion of the First Merger will depend on the market value of CECO common stock at the time of completion of the First Merger. The share price of CECO common stock is by nature subject to the general price fluctuations in the market for publicly traded equity securities and has historically experienced volatility. Met-Pro and CECO cannot predict the market price of CECO common stock at any time, including before or after the completion of the First Merger. Differences in the market price of CECO common stock may be the result of changes in the business, operations or prospects of CECO, market reactions to the proposed Mergers, regulatory considerations, general market and economic conditions or other factors.

As a result of the collar, the value of the shares of CECO common stock issued to Met-Pro shareholders in the First Merger may be greater or lesser than $13.75, which difference may be material. Shareholders of Met-Pro electing to receive stock consideration or receiving stock consideration as a result of the proration provisions of the Merger Agreement will receive between 1.0000 and 1.3520 shares of CECO common stock for each share of Met-Pro common stock entitled to receive stock consideration. The exact exchange ratio is determined by dividing $13.75 by the volume weighted average closing price of CECO’s common stock for the 15-day trading day period ending on the last trading date before the closing of the First Merger. Accordingly, if the volume weighted average trading price of CECO common stock for the 15-day trading period ending on the last trading date before the closing of the First Merger is less than $10.17, such shares will be valued at $10.17 for purposes of determining the Merger Consideration. For example, if the volume weighted average trading price of CECO common stock for the 15-day trading day period ending on the trading day before the closing of the First Merger is $9.00, Met-Pro shareholders electing to receive

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CECO common stock would receive CECO common stock valued at $12.17 rather than $13.75. Further decreases in the market price of CECO common stock would further reduce the value of the consideration to be received by the Met-Pro shareholders entitled to receive CECO common stock in the First Merger. Conversely, if the volume weighted average trading price of CECO common stock for the 15-day trading day period ending on the day before the closing of the First Merger is $15.00, Met-Pro shareholders electing to receive shares of CECO common stock would receive shares valued at $15.00 rather than $13.75. Further increases in the market price of CECO common stock would further increase the value of the consideration to be received by the Met-Pro shareholders entitled to receive CECO common stock in the First Merger. During the past 12 months, shares of CECO common stock have traded between $7.70 and $14.32, and remain subject to market forces and resulting price fluctuation. There can, therefore, be no assurance that Met-Pro shareholders that receive stock consideration will receive $13.75 of value per share upon completion of the First Merger. Because of the proration provisions included in the Merger Agreement, Met-Pro shareholders electing to receive cash may, depending on the number of shares for which cash elections are made, receive shares of CECO common stock in partial payment for the Merger Consideration.

You may receive a form of consideration different from what you elect, which could have an effect on your tax situation. Regardless of the cash or stock elections made by Met-Pro shareholders, the Merger Agreement contains proration procedures that are designed to ensure that (i) approximately 53% of the Met-Pro shares (treating all Equity Award Shares as outstanding shares) will be exchanged for cash (which, together with the amount of cash paid for Equity Award Shares, is capped at $109.5 million) and (ii) approximately 47% of the Met-Pro shares outstanding immediately prior to the Mergers are converted in the Mergers into the right to receive CECO common stock. As a result, if more than 53% of Met-Pro’s shares are subject to cash elections (treating all Equity Award Shares as outstanding shares subject to cash elections), those shareholders who properly make cash elections will receive CECO common stock for a portion of their Met-Pro shares. If less than 53% of Met-Pro’s shares are subject to cash elections (treating all Equity Award Shares as outstanding shares subject to cash elections), those shareholders who properly make stock elections may receive cash consideration for a portion of their Met-Pro shares. Please refer to the section entitled “The Mergers—Met-Pro Shareholders Making Cash and Stock Elections” beginning on page 90. There is a risk that you will receive a portion of the Merger Consideration in the form that you do not elect that could result in, among other things, tax consequences that differ from those that would have resulted had you received the form of consideration you elected, including with respect to the recognition of taxable gain to the extent cash is received. This could also result in the receipt of value that is materially different than the value you would have received if you received the form of consideration you elected.

After making a cash election or a stock election, you will not be able to sell the Met-Pro shares covered by your election, unless you revoke your election at or prior to the election deadline or unless the Merger Agreement is terminated. The deadline for making cash elections and stock elections is 5:00 p.m., Eastern Time, on the date that is one business day before the date of the Met-Pro special meeting (or such other date as CECO and Met-Pro mutually agree). CECO and Met-Pro will publicly announce the anticipated election deadline at least five business days before the date of the Met-Pro special meeting. After you make a cash or stock election and prior to completion of the First Merger, the trading price of Met-Pro common stock or CECO common stock may decrease, and you may otherwise want to sell Met-Pro shares to gain access to cash, make other investments, or eliminate the potential for a decrease in the value of your investment. However, once you make an election with respect to any shares of Met-Pro common stock, you will not be able to sell those shares, unless you properly revoke your election at or prior to the election deadline or the Merger Agreement is terminated. Please refer to the section entitled “The Mergers—Met-Pro Shareholders Making Cash and Stock Elections” beginning on page 90.

The price of CECO common stock may be affected by factors different from those affecting the price of Met-Pro common stock. Upon completion of the First Merger, holders of Met-Pro common stock who elect to receive CECO common stock or who received CECO stock as a result of the proration procedures in the Merger Agreement described herein will become CECO stockholders. Since CECO’s business differs from Met-Pro’s business, the results of operations and the market price of CECO common stock may be affected by factors different than those affecting Met-Pro’s results of operations and the market price of Met-Pro common stock. For

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a discussion of CECO’s and Met-Pro’s businesses and certain factors to consider in connection with their respective businesses, please see CECO’s Form 10-K for the year ended December 31, 2012 filed with the SEC, including the section entitled “Risk Factors,” and Met-Pro’s Form 10-K for the year ended January 31, 2013 filed with the SEC, including the section entitled “Risk Factors,” and the other periodic reports and other documents of CECO and Met-Pro incorporated by reference into this joint proxy statement/prospectus and listed in the section entitled “Where You Can Find More Information” beginning on page 179.

The U.S. federal income tax treatment of the Mergers will not be known at the Merger Consideration election deadline or the time of the Met-Pro or CECO special meetings, and any position taken that the Mergers qualify as a “reorganization” might successfully be challenged by the Internal Revenue Service. The U.S. federal income tax consequences to Met-Pro shareholders of the Mergers will depend on whether those transactions qualify as a reorganization under Section 368(a) of the Code. If on or before the closing date of the First Merger Met-Pro receives an opinion from its counsel, Fox Rothschild LLP, and CECO receives an opinion from its counsel, Barnes & Thornburg LLP, in each case that the Mergers qualify as a reorganization, then Met-Pro and CECO will each report the transactions as a reorganization under Section 368(a) of the Code.

If the Mergers qualify as a reorganization under Section 368(a) of the Code, U.S. holders generally will recognize gain, but not loss, on the exchange in an amount equal to the lesser of (i) the amount of cash treated as received in exchange for Met-Pro common stock in the First Merger or (ii) the excess of the “amount realized” in the transaction ( i.e., the fair market value of CECO common stock at the Effective Time plus the amount of cash treated as received in exchange for Met-Pro common stock in the First Merger) over their tax basis in the surrendered Met-Pro common stock. If either Met-Pro or CECO does not receive such an opinion, Met-Pro and CECO will each treat the transactions as a taxable disposition of the Met-Pro common stock by the Met-Pro shareholders to CECO.

Delivery of these opinions is not a condition to the closing of the Mergers, however, and no assurance can be given that the opinions will be delivered. It will not be known at the Merger Consideration election deadline or the time of the Met-Pro special meeting whether the opinions will be forthcoming and, therefore, the tax treatment of the Mergers will not be known at such time. CECO will make a public announcement on or soon after the Effective Time as to whether or not the opinions described above have been delivered. Neither CECO nor Met-Pro will resolicit shareholder votes, nor reopen the Merger Consideration election period, in the event that the Mergers do not qualify as a reorganization under Section 368(a) of the Code. Therefore, there is a risk that the anticipated tax treatment of the Mergers to Met-Pro shareholders may adversely change following the election deadline and the date of the Met-Pro special meeting.

Furthermore, even if the opinions are received and the parties treat the Mergers as a reorganization under Section 368(a) of the Code, the Internal Revenue Service (the “IRS”) might successfully assert a contrary position. Qualification as a reorganization under Section 368(a) of the Code depends on the satisfaction of a number of requirements, including compliance with the continuity of interest test, which will depend on the value of the CECO common stock at the Effective Time and the effects of the exchange ratio adjustment provisions in the Merger Agreement.

Even if the Mergers qualify as a “reorganization” under Section 368(a) of the Code for U.S. federal income tax purposes, as a result of the cash received in the First Merger, Met-Pro shareholders might recognize all or a significant portion of any gain realized on the exchange of their Met-Pro common stock. As a result of the cash treated as received in exchange for Met-Pro common stock in the First Merger, a U.S. holder of Met-Pro common stock might recognize a significant portion of gain on the exchange, even if the Mergers qualify as a reorganization under Section 368(a) of the Code.

The Merger Agreement contains provisions that could discourage a potential competing acquiror that might be willing to pay more to effect a business combination with Met-Pro. The Merger Agreement contains “non-solicitation” provisions that restrict Met-Pro’s ability to solicit or facilitate proposals regarding a merger or similar transaction with another party. Further, several conditions must be satisfied in order for the Met-Pro board of directors to withdraw, amend or modify its recommendation regarding the proposed First

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Merger. Please refer to the section entitled “The Merger Agreement—Non-Solicitation; Superior Proposals” beginning on page 114. If the Met-Pro board of directors withdraws, amends or modifies its recommendation regarding the proposed First Merger, CECO has the right to terminate the Merger Agreement and receive a $6,740,000 termination fee from Met-Pro. These provisions could discourage a potential competing acquiror from considering or proposing an acquisition of Met-Pro, even if such a potential competing acquirer were prepared to pay consideration with a higher value than the cash and shares proposed to be issued in the First Merger, or might result in a potential competing acquiror proposing to pay a lower per share price than it might otherwise have proposed to pay because of the added expense of the termination fee.

Pending litigation against Met-Pro could result in an injunction preventing the completion of the Mergers or a judgment resulting in the payment of damages in the event the Mergers are completed and may adversely affect the combined company’s business, financial condition or results of operations and cash flows following the Mergers. Met-Pro and the Met-Pro board of directors are named as defendants in a putative class action lawsuit brought by an alleged Met-Pro shareholder challenging the proposed Mergers. Among other remedies, the plaintiff seeks to enjoin the Mergers. The outcome of this litigation is uncertain. If the case is not resolved, these lawsuits could prevent or delay completion of the Mergers and result in costs to Met-Pro, including any costs associated with the indemnification of directors and officers. There can be no assurance that additional lawsuits will not be filed against Met-Pro, CECO and/or their respective directors and officers in connection with the Mergers. The defense or settlement of any lawsuit or claim that remains unresolved at the time the Mergers are completed may adversely affect the combined company’s business, financial condition, results of operations and cash flows. Met-Pro has entered into a memorandum of understanding with the plaintiff to settle the lawsuit, as described below in the section entitled “The Mergers—Legal Proceedings Related to the Mergers” beginning on page 85.

Met-Pro did not solicit proposals from other potential bidders and did not have contact with any potential buyers other than CECO during the negotiations leading up to the execution of the Merger Agreement, which may mean that the Merger Consideration does not adequately value Met-Pro . Met-Pro did not conduct a “market check” or have contact with potential buyers other than CECO prior to the execution of the Merger Agreement. A hypothetical buyer could potentially have offered to acquire Met-Pro for an amount of consideration greater, and/or upon more favorable terms, than the Merger Consideration to be paid by CECO to Met-Pro shareholders pursuant to the Merger Agreement.

The integration of CECO and Met-Pro following the Mergers may present significant challenges and impair CECO’s ability to realize the anticipated benefits of the Mergers. CECO may face significant challenges in combining Met-Pro’s operations into its operations in a timely and efficient manner and in retaining key Met-Pro personnel. The failure to integrate successfully CECO and Met-Pro and to manage successfully the challenges presented by the integration process may result in CECO not achieving the anticipated benefits of the Mergers including operational and financial synergies which may have the effect of depressing the market price of the CECO common stock issued in the Mergers.

Restrictions in CECO’s debt agreements may prevent CECO from paying dividends. CECO’s ability to pay dividends will be restricted by current and future agreements governing its debt, including its current credit agreement and the financing agreements expected to be in place upon consummation of the First Merger. Please refer to the section entitled “Debt Financing” beginning on page 132.

CECO will have a substantial amount of debt outstanding following the Mergers and may incur additional indebtedness in the future, which could restrict CECO’s ability to pay dividends and fund working capital and planned capital expenditures. CECO will incur substantial debt in the approximate amount of $80.2 million in order to complete the Mergers and repay Met-Pro’s debt. This amount of leverage could have important consequences, including:

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CECO currently expects its cash interest expense to be approximately $0.6 to 0.7 million in fiscal year 2013 assuming consummation of the Mergers by August 31, 2013. Future interest expense will be significantly higher than historic interest expense as a result of higher levels of indebtedness incurred to consummate the Mergers. CECO’s ability to make payments on its debt and to pay dividends on its common stock will depend on its ability to generate cash in the future, which will depend on many factors beyond its control. CECO cannot assure you that:

If CECO cannot generate sufficient cash from its operations to meet its debt service obligations, CECO may need to reduce or delay capital expenditures, the development of its business generally and any acquisitions. If CECO becomes unable to meet its debt service and repayment obligations, CECO would be in default under the terms of its credit agreement, which would allow its lenders to declare all outstanding borrowings to be due and payable. If the amounts outstanding under its credit facilities were to be accelerated, CECO cannot assure you that its assets would be sufficient to repay in full the money owed.

Obtaining required approvals and satisfying closing conditions may delay or prevent completion of the Mergers and may significantly reduce the benefits anticipated to be realized from the Mergers or could adversely affect the market price of CECO common stock or Met-Pro common stock or their future business and financial results. Completion of the Mergers is conditioned upon Met-Pro’s shareholders adopting, at the Met-Pro special meeting, the Merger Agreement, and CECO’s stockholders approving, at the CECO special meeting, the issuance of CECO common stock to Met-Pro shareholders in the First Merger. If the shareholders of Met-Pro or the stockholders of CECO do not approve these matters at their respective special meetings, the Mergers will not be consummated. Such conditions may jeopardize or delay completion of the Mergers or may reduce the anticipated benefits of the Mergers. Further, no assurance can be given that the required consents and approvals will be obtained or that the required conditions to closing will be satisfied. Even if all such consents and approvals are obtained, no assurance can be given as to the terms, conditions and timing of the consents and approvals or that they will satisfy the terms of the Merger Agreement. Please refer to the section entitled “The Merger Agreement—Conditions of the Mergers” beginning on page 122 for a discussion of the conditions to the completion of the Mergers for a discussion of the parties’ obligations to cooperate (including certain limitations thereon) with respect to the receipt of such consents and approvals. If the Mergers are not completed by October 31, 2013, assuming the outside date for completing the Mergers is automatically extended under the terms of the Merger Agreement from September 30, 2013 to October 31, 2013 and that the parties to the Merger Agreement do not further extend this deadline by written agreement, either Met-Pro or CECO may terminate the Merger Agreement. Please refer to the section entitled “The Merger Agreement—Termination; Termination Fees” beginning on page 124.

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Met-Pro expect to incur costs associated with transaction fees and other costs related to the Mergers. Specifically, CECO expects to incur approximately $5.5 million of transaction costs related to the Mergers. In addition, CECO will incur integration and restructuring costs following the completion of the Mergers as it integrates the businesses of Met-Pro with those of CECO. Although CECO expects that the realization of efficiencies related to the integration of the businesses will offset incremental transaction, integration and restructuring costs over time, CECO cannot give any assurance that this net benefit will be achieved in the near term, or at all.

The Mergers may not be accretive and may cause dilution to the combined company’s earnings per share, which may negatively affect the price of the common stock of the combined company following completion of the Mergers. CECO currently anticipates that the Mergers will be accretive to the earnings per share of the combined company during the first full calendar year after the Mergers are completed in an estimated amount of between 11.5% and 33.1%. This expectation is based on preliminary estimates and assumes certain synergies expected to be realized by the combined company during such time, including $9 million of cost savings. Such estimates and assumptions could materially change due to additional transaction-related costs, the failure to realize any or all of the benefits expected in the Mergers or other factors beyond the control of CECO and Met-Pro. All of these factors could delay, decrease or eliminate the expected accretive effect of the Mergers and cause resulting dilution to the combined company’s earnings per share or to the price of the common stock of the combined company.

The issuance of additional shares of CECO common stock in connection with the First Merger may cause the market price of CECO common stock to decline. In connection with the completion of the Mergers, based on the number of shares outstanding on the record date, CECO expects to issue between approximately 7.1 million and 9.6 million shares of CECO common stock, which will represent between approximately 27.7% and 34.1% of the issued and outstanding shares of CECO after completion of the Mergers. The issuance of this amount of new shares may cause the market price of CECO common stock to decline.

Met-Pro shareholders will have ownership and voting interests in CECO after the Mergers lower than they did in Met-Pro and will exercise less influence over management of CECO than they currently exercise over management of Met-Pro. After the Effective Time, Met-Pro shareholders who receive stock consideration in the First Merger will own in the aggregate a significantly smaller percentage of CECO common stock than they currently own of Met-Pro common stock. Immediately following the Mergers, those shareholders are expected to own in the aggregate (excluding any shares of CECO common stock they may own or acquire prior to consummation of the First Merger) between approximately 27.7% and 34.1% of the outstanding shares of CECO common stock, based on the number of shares of Met-Pro common stock and CECO common stock outstanding on the record date. Consequently, Met-Pro shareholders, as a general matter, will have less influence over the management and policies of CECO than they currently exercise over the management and policies of Met-Pro.

The shares of CECO common stock to be received by Met-Pro shareholders as a result of the First Merger will have different rights from the shares of Met-Pro common stock. Met-Pro shareholders’ rights are currently governed by the Met-Pro articles of incorporation, the Met-Pro bylaws and Pennsylvania law. Those Met-Pro shareholders who receive stock consideration in the First Merger will, upon completion of the First Merger, become stockholders of CECO and their rights will be governed by the CECO certificate of incorporation, the CECO by-laws and Delaware law. Please refer to the section entitled “Comparison of Rights of Common Shareholders of Met-Pro and Common Stockholders of CECO” beginning on page 144.

If the financing contemplated by the Commitment Letter is not available, or alternative financing cannot be secured, the Mergers may not be completed and CECO may be required to pay a termination fee to Met-Pro. CECO intends to finance the cash required in connection with the Mergers, including for expenses incurred in connection with the Mergers, with debt financing in accordance with the terms of the Commitment Letter. The Commitment Letter provides for a senior secured amortizing term loan facility in the aggregate principal amount of $65 million and a senior secured revolving credit facility for loans

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and letters of credit in the aggregate principal amount of up to $60 million (collectively, the “Senior Credit Facilities”); provided that the Senior Credit Facilities may be increased by up to $30 million in the aggregate, with a minimum borrowing by CECO of not less than $10 million, without further consent of the lenders party thereto, although such lenders have no commitment or obligation to provide such incremental financing. Although CECO anticipates that the senior secured revolving credit facility will be $90 million, for aggregate loan facilities of $155 million, Bank of America, N.A. is not committed to fund the additional $30 million. The closing of the Senior Credit Facilities is subject to the satisfaction of certain conditions, including no material adverse effect having occurred with respect to CECO and its subsidiaries or Met-Pro and its subsidiaries, in each case, taken as a whole, the negotiation, execution and delivery of definitive loan and security documentation for the Senior Credit Facilities, and other customary closing conditions. For a more detailed discussion of the debt financing, see the section entitled “Debt Financing” beginning on page 132.

In the event some or all of the financing contemplated by the Commitment Letter is not available, CECO is obligated to use its commercially reasonable efforts to obtain alternative financing in an amount that will enable CECO to consummate the Mergers, even if such alternative financing is on less favorable terms and conditions than those contemplated by the Commitment Letter. If financing cannot be obtained, the Mergers may not be completed. Due to the fact that there is no funding condition in the Merger Agreement, if CECO is unable to obtain funding from its financing sources for the cash required in connection with the Mergers, CECO could be in breach of the Merger Agreement assuming all other conditions to closing are satisfied and may be liable to Met-Pro for damages or a termination fee of $10,365,000.

Certain directors and executive officers of CECO may have potential conflicts of interest which may influence their support of the Mergers . Some of CECO’s directors and executive officers have interests in the Mergers that are different from, or in addition to, those of CECO stockholders generally. Each of the directors and executive officers of CECO, with the possible exception of Benton Cook, is expected to maintain their position as a director or executive officer with the combined company after completion of the Mergers, and directors and/or executive officers may be awarded bonuses for their work in closing the Mergers. As of the date of this joint proxy statement/prospectus, no agreement to award any such a bonus is currently in place. As a result, CECO directors and officers may be more likely to support the issuance of shares of CECO common stock to Met-Pro shareholders in the First Merger than if they did not have those interests. Please refer to the section entitled “The Mergers—Interests of CECO Directors and Executive Officers in the Mergers” beginning on page 84 for a discussion of these interests.

Certain directors and executive officers of Met-Pro may have potential conflicts of interest which may influence their support of the adoption of the Merger Agreement. Some of Met-Pro’s directors and executive officers have interests in the Mergers that are different from, or in addition to, those of Met-Pro shareholders generally. Although the Met-Pro directors will not become directors of CECO after the Mergers, CECO will indemnify and maintain liability insurance for all of the directors of Met-Pro for their services as directors before the Mergers. In addition, each of the executive officers of Met-Pro is expected to maintain his employment with the combined company after completion of the Mergers and is entitled to severance payments if his employment were to terminate following the Mergers under specific circumstances. The Merger Agreement also provides that the equity awards held by Met-Pro executive officers and directors will accelerate and be cashed out in connection with the First Merger. The equity awards held by the Met-Pro executive officers and directors that will be cashed out in connection with the First Merger will be deducted from the cash consideration that would otherwise be paid to Met-Pro shareholders in the First Merger and, unlike the shares held by Met-Pro shareholders, will not be subject to the proration and reallocation procedures in the Merger Agreement in the event that the cash elections by the Met-Pro shareholders are oversubscribed, as described below in more detail in the section entitled “Met-Pro Shareholders Making Cash and Stock Elections—Proration and Reallocation Procedures” beginning on page 92. As a result, Met-Pro directors and officers may be more likely to support the adoption of the of the Merger Agreement and the approval of the Mergers than if they did not have those interests. Please refer to the section entitled “The Mergers—Interests of Met-Pro Directors and Executive Officers in the Mergers” beginning on page 82 for a discussion of these interests. Upon the consummation of the

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Merger, the Met-Pro directors and executive officers will be entitled to receive aggregate benefits and payments in connection with the Merger consisting of cash in payment for outstanding equity awards, payments under Met-Pro’s FYE 2014 Management Incentive Plan, severance payments, and payments under Met-Pro’s supplemental executive retirement plans, with an approximate value of $7,707,656.

The exercise of Met-Pro’s directors’ and executive officers’ discretion in agreeing to changes or waivers in the terms of the Merger Agreement may result in a conflict of interest when determining whether such changes to the terms of the Merger Agreement or waivers of conditions are appropriate and in Met-Pro’s shareholders’ best interest. In the period leading up to the closing of the First Merger, events may occur that would cause Met-Pro to agree to amend the Merger Agreement, to consent to certain actions taken by CECO, or to waive rights that Met-Pro is entitled to under the Merger Agreement. Such events could arise because of a request by CECO to undertake actions that would otherwise be prohibited by the terms of the Merger Agreement. In any of such circumstances, the Met-Pro board of directors would have discretion as to whether to grant its consent or waive its rights. The existence of the financial and personal interests of Met-Pro’s directors and executive officers described in the preceding risk factors may result in a conflict of interest on the part of one or more of the directors or the executive officers between what he or she may believe is best for Met-Pro and what he or she may believe is best for himself or herself in determining whether or not to take the requested action. As of the date of this joint proxy statement/prospectus, Met-Pro does not believe there will be any changes or waivers that its directors and officers would be likely to make after shareholder approval of the merger proposal has been obtained. Although certain changes could be made without further shareholder approval, Met-Pro will circulate a new or amended joint proxy statement/prospectus and resolicit approval of the First Merger from its shareholders, to the extent required by law, if changes to the terms of, or waivers under, the Merger Agreement could render the statements in this joint proxy statement/prospectus materially misleading.

Whether or not the Mergers are completed, the pendency of the transaction could cause disruptions in the businesses of Met-Pro and CECO, which could have an adverse effect on their businesses and financial results. These disruptions could include the following:

The unaudited pro forma financial statements are presented for illustrative purposes only and should not be viewed as a forecast of CECO’s financial condition or results of operations following the Mergers. The unaudited pro forma financial statements have been derived from the historical financial statements of CECO and Met-Pro and certain adjustments and assumptions have been made regarding CECO after giving effect to the Mergers. The information upon which these adjustments and assumptions have been made is preliminary, and these kinds of adjustments and assumptions are difficult to make with complete accuracy. Moreover, the unaudited pro forma financial statements do not reflect all costs that are expected to be incurred or savings to be achieved by the combined company in connection with the Mergers. For example, neither the impact of any incremental costs incurred in integrating the two companies, nor any potential cost savings is reflected in the unaudited pro forma financial statements. As a result, the actual financial condition and results of operations of CECO following the Mergers will likely not be consistent with, or evident from, and may differ materially from, these unaudited pro forma financial statements. In addition, the assumptions used in preparing the unaudited pro forma financial information may not prove to be accurate, and other factors may affect CECO’s financial condition or results of operations following the Mergers. Therefore, stockholders of CECO and the shareholders of Met-Pro should not place undue reliance on the pro forma financial statements when

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deciding whether to vote for their respective proposals relating to the Mergers. Please refer to the section entitled “Unaudited Pro Forma Condensed Combined Financial Statements” beginning on page 134.

Delay or failure to complete the Mergers would prevent CECO and Met-Pro from realizing the anticipated benefits of the Mergers and each company would also remain liable for significant transaction costs, including legal, accounting and financial advisory fees. Any delay in completing the Mergers may significantly reduce the synergies and other benefits anticipated by CECO if it successfully completes the Mergers within the expected timeframe and integrates the businesses of Met-Pro and CECO. In addition, the market price of each company’s common stock may reflect various market assumptions as to whether and when the Mergers will be completed. Consequently, the completion of, the failure to complete, or any delay in the completion of the Mergers could result in significant changes in the respective market prices of CECO or Met-Pro common stock.

Risks Related to Met-Pro If the Mergers Are Not Completed

If the Mergers are not completed, the price of Met-Pro common stock and future business and operations could be harmed. If the Mergers are not completed, Met-Pro may be subject to the following material risks, among others:

Shareholders may sell substantial amounts of Met-Pro common stock in the public market, which is likely to depress the price of Met-Pro common stock. A significant number of shares of Met-Pro common stock may be sold at any time prior to the Mergers. If Met-Pro’s current shareholders sell Met-Pro common stock in the public market prior to the Mergers, it is likely that arbitrageurs will acquire such shares. These arbitrageurs would likely sell all such shares in the public market immediately following any announcement, or anticipated announcement, that the Mergers failed, or will likely fail, to close for any reason, which in turn would likely cause the market price of Met-Pro common stock to decline. In addition to the other negative effects on Met-Pro, such sales of Met-Pro common stock might make it more difficult for Met-Pro to sell equity or equity-related securities in the future if the Mergers are not completed.

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Risks Relating to Met-Pro

Met-Pro is, and will continue to be, subject to the risks described in Part I, Item 1A in Met-Pro’s Annual Report on Form 10-K for the year ended January 31, 2013, filed with the SEC on March 21, 2013 and incorporated by reference into this joint proxy statement/prospectus. See the section entitled “Where You Can Find More Information” beginning on page 179 for the location of information incorporated by reference into this joint proxy statement/prospectus.

Risks Relating to CECO

CECO is, and will continue to be, subject to the risks described in Part I, Item 1A in CECO’s Annual Report on Form 10-K for the year ended December 31, 2012, filed with the SEC on March 15, 2013 and incorporated by reference into this joint proxy statement/prospectus. See the section entitled “Where You Can Find More Information” beginning on page 179 for the location of information incorporated by reference into this joint proxy statement/prospectus.

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SELECTED HISTORICAL CONSOLIDATED FINANCIAL INFORMATION OF

CECO ENVIRONMENTAL CORP.

The following table sets forth selected historical consolidated financial information of CECO for the periods presented. The selected financial information, as of December 31, 2012, 2011, 2010, 2009 and 2008 and for each of the five fiscal years then ended, has been derived from CECO’s audited consolidated financial statements. The selected financial information for the three months ended March 31, 2013 and 2012 has been derived from CECO’s unaudited condensed consolidated financial statements. The selected financial information includes, in the opinion of CECO’s management, all adjustments, consisting of normal recurring adjustments, necessary to present fairly the results of operations and financial position of CECO for the periods and dates presented.

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SELECTED HISTORICAL CONSOLIDATED FINANCIAL

INFORMATION OF MET-PRO CORPORATION

The following table sets forth selected historical consolidated financial information of Met-Pro for the periods presented. The selected financial information, as of January 31, 2013, 2012, 2011, 2010 and 2009 and for each of the five fiscal years then ended, has been derived from Met-Pro’s audited consolidated financial statements. The selected financial information for the three months ended April 30, 2013 and 2012 has been derived from Met-Pro’s unaudited condensed consolidated financial statements. The selected financial information includes, in the opinion of Met-Pro’s management, all adjustments, consisting of normal recurring adjustments, necessary to present fairly the results of operations and financial position of Met-Pro for the periods and dates presented.