THIRD AMENDMENT

EXHIBIT 10.1

EXECUTION VERSION

THIRD AMENDMENT

TO

CREDIT AGREEMENT

THIS THIRD AMENDMENT TO CREDIT AGREEMENT (this “Amendment”), dated as of February 29, 2008 (the “Effective Date”), by and among, on the one hand, CECO ENVIRONMENTAL CORP., a Delaware corporation (“Parent”), CECO GROUP, INC., a Delaware corporation (“Group”) and each of the following Subsidiaries of Parent as Borrowers under this Amendment and the Credit Agreement: CECO FILTERS, INC., a Delaware corporation (“Filters”), NEW BUSCH CO., INC., a Delaware corporation (“New Busch”), THE KIRK & BLUM MANUFACTURING COMPANY, an Ohio corporation (“K&B”), KBD/TECHNIC, INC., an Indiana corporation (“Technic”), CECOAIRE, INC., a Delaware corporation (“Aire”), CECO ABATEMENT SYSTEMS, INC., a Delaware corporation (“Abatement”), H.M. WHITE, INC., a Delaware corporation (“H.M. White”), EFFOX INC., formerly known as CECO ACQUISITION CORP., a Delaware corporation (“Effox”), GMD ENVIRONMENTAL TECHNOLOGIES, INC. formerly known as GMD ACQUISITION CORP., a Delaware corporation (“GMD”), FKI, LLC, a Delaware limited liability company (“FKI LLC”), CECO MEXICO HOLDINGS LLC, a Delaware limited liability company (“CECO Mexico LLC”), and FKI ACQUISITION CORP., a Delaware corporation (“FKI Acquisition”), and, on the other hand, FIFTH THIRD BANK, an Ohio banking corporation (“Lender”), is as follows:

Preliminary Statements

A. Parent, Group and Borrowers (the “Loan Parties”) and Lender are parties to a Credit Agreement dated as of December 29, 2005, as amended by the First Amendment to Credit Agreement dated as of June 8, 2006 and the Second Amendment to Credit Agreement dated as of February 28, 2007 (as amended, the “Credit Agreement”). Capitalized terms which are used, but not defined, in this Amendment will have the meanings given to them in the Credit Agreement.

B. The Loan Parties have requested that Lender: (i) consent to the FKI Acquisition; (ii) increase the maximum Revolving Loan Commitment from $20,000,000 to $30,000,000 (subject to availability); (iii) make an additional term loan in the aggregate amount of $5,000,000 to finance, in part, the FKI Acquisition; (iv) increase the maximum capital expenditures Financial Covenant in Fiscal Year 2007 to $2,000,000 and commencing with Fiscal Year 2008 to $2,500,000; (v) make certain changes to the incentive pricing with respect to LOC Fee, to be based upon Borrowers’ Fixed Charge Coverage Ratio; and (vi) make certain other amendments to the Credit Agreement and certain of the other Loan Documents.

C. Lender is willing to consent to such requests and to so amend the Credit Agreement and other Loan Documents, all on the terms, and subject to the conditions, of this Amendment.

Statement of Agreement

In consideration of the mutual covenants and agreements set forth in this Amendment, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, Lender and the Loan Parties hereby agree as follows:

1. Amendments to Credit Agreement. Subject to the satisfaction of the conditions of this Amendment, the Credit Agreement is hereby amended as follows:

1.1 Section 1.1 of the Credit Agreement is hereby amended by the addition of the following definitions, in their proper alphabetical order, to provide in their entirety as follows:

“CECO Environmental Mexico” means CECO Environmental Mexico, S. de R.L. de C.V., a company organized under the laws of Mexico.

“CECO Environmental Services” means CECO Environmental Services, S. de R.L. de C.V., a company organized under the laws of Mexico.

“CECO Mexico LLC” means CECO Mexico Holdings LLC, a Delaware LLC.

“CECO India” means CECO Filters India Private Limited, a corporation organized and existing under the laws of India.

“FKI Acquisition Corp.” means FKI Acquisition Corp., a Delaware corporation, and its successors and assigns.

“FKI” means Fisher-Klosterman, Inc., a Kentucky corporation.

“FKI Acquisition” means the acquisition by FKI Acquisition Corp. of substantially all of the assets of FKI, all in accordance with, and pursuant to the terms of, the FKI Acquisition Documents.

“FKI Acquisition Agreement” means the Asset Purchase Agreement dated as of February 1, 2008 by and among Parent, FKI Acquisition Corp., FKI, and the other parties thereto.

“FKI Acquisition Documents” means the FKI Acquisition Agreement and every other document or agreement executed or delivered by any Loan Party in connection with the FKI Acquisition.

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“FKI Earn-out Payment” means any Earn-Out Payment (as defined in the FKI Acquisition Agreement) paid by a Loan Party in accordance with the FKI Acquisition Agreement.

“Fisher Klosterman Shanghai” means Fisher Klosterman Buell Shanghai Company, Ltd., a company organized under the laws of China.

“FKI, LLC” means FKI, LLC, a Delaware limited liability company.

“GMD” means GMD Environmental Technologies, Inc., formerly known as GMD Acquisition Corp., a Delaware corporation.

“Term Loan C” has the meaning given in Section 2.2(a).

“Term Loan Note C” has the meaning given in Section 2.2(a).

“Third Amendment” means the Third Amendment to this Agreement dated as of February 29, 2008.

1.2 The following definitions in Section 1.1 of the Credit Agreement are hereby amended in their entirety by substituting the following in their respective steads:

“Affiliate” means, as to any Person (the “Subject Person”), any other Person which, directly or indirectly, is in control of, is controlled by, or is under common control with, the Subject Person. For purposes of this definition, “control” of a Person means the power, direct or indirect, (a) to vote 5% or more of the securities (or other Ownership Interests) having voting power for the election of directors (or managers in the case of a limited liability company) of the Person or (b) otherwise to direct or cause the direction of the management and policies of the Person, whether by contract or otherwise. Without limiting the generality of the foregoing, each of the following will be deemed an Affiliate of a Borrower for purposes of this Agreement, Parent, Group, FKI, LLC, CECO Mexico LLC, CECO India, Fisher Klosterman Shanghai, CECO Environmental Mexico, CECO Environmental Services and each officer and director of a Loan Party.

“Adjusted EBITDA” means the total (without duplication and all as determined on a consolidated basis in accordance with GAAP), in Dollars, of EBITDA for the applicable period, (a) minus Non-financed Capital Expenditures for that same period, exclusive of Excluded Capital Expenditures (as defined in Section 5.3); (b) minus the aggregate cash amount of the Loan Parties’ income and franchise tax expense for that same period to the extent deducted in the determination of Net Income; (c) minus any gain or plus any non-cash loss arising from the sale of capital assets to the extent included or

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deducted in the determination of Net Income; (d) minus any gain arising from the write-up of any assets (excluding inventory) or plus any non-cash loss from the write-down of any assets, each to the extent included (or deducted in the case of non-cash losses) in the determination of Net Income; (e) minus any extraordinary gains and items of income to the extent included in the determination of Net Income or plus any non-cash extraordinary items of loss to the extent deducted in the determination of Net Income; (f) minus any gains (or plus any non-cash losses) recognized by the Loan Parties as earnings which relate to adjustments made by the Loan Parties as a result of any extraordinary accounting adjustment to the extent included (or deducted in the case of non-cash losses) in the determination of Net Income; (g) minus non-operating, non-recurring gains (or plus any non-cash losses) from time to time occurring to the extent included (or deducted in the case of non-cash losses) in the determination of Net Income; (h) plus any non-cash expense or minus any non-cash gain or income during such period resulting from (i) a change in the price of Parent’s common stock opposite the strike price of its options and warrants outstanding from time to time, (ii) stock option expenses, and (iii) impairment of goodwill; (i) minus the aggregate amount of any dividends to Parent’s stockholders, if any, permitted expressly by Lender which are paid in cash by Parent during the applicable period; and (j) minus the aggregate amount of Effox Earn-out Payments and FKI Earn-out Payments made by any Loan Party in cash during the applicable period to the extent not deducted in the determination of Net Income which was used to determine such EBITDA. The term “applicable period” in this definition means Test Period in the case of determining the Fixed Charge Coverage Ratio or the Maximum Total Funded Debt to Adjusted EBITDA Ratio and Fiscal Year in the case of determining Excess Cash Flow.

“Applicable LOC Fee Percentage” means, as of any date, the applicable percentage shown in the applicable column in the table below based on the then applicable Fixed Charge Coverage Ratio. As of the Effective Date (as defined in the Third Amendment), the Applicable LOC Fee Percentage is 1.0% (i.e., Pricing Grid Level 3).

“Borrower” means each of Filters, New Busch, K&B, Technic, Aire, Abatement, H.M. White, CECO Acquisition (now known as Effox Inc.), GMD, FKI Acquisition and the Domestic Subsidiaries of Parent or Group hereafter becoming a party to this Agreement pursuant to Section 5.9(b), and “Borrowers” means, collectively, Filters, New Busch, K&B,

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Technic, Aire, Abatement, H.M. White, CECO Acquisition (now known as Effox Inc.), GMD, FKI Acquisition and such additional Domestic Subsidiaries. To the extent a term or provision of this Agreement or any of the other Loan Documents is applicable to a “Borrower”, it is applicable to each and every Borrower unless the context expressly indicates otherwise. For the avoidance of doubt, neither FKI, LLC nor CECO Mexico LLC shall be a Borrower.

“Excess Cash Flow Payment” has the meaning given in Section 2.2(c)(iv).

“Fixed Charges” means, for the applicable period, the total (without duplication), in Dollars, of (all as determined on a consolidated basis in accordance with GAAP): (a) the principal amount of the Loan Parties’ long-term Indebtedness, in each case paid during the applicable period, including those under Term Loan Note C (other than any Excess Cash Flow Payment with respect to Term Loan C), the ICS Note, the Sandler Note, and the Subordinated Debt Notes (as defined within the definition of Subordinated Debt Documents) (whether classified, as of any date, as long-term Indebtedness); plus (b) scheduled capital lease payments by the Loan Parties during the applicable period; and plus (c) the Loan Parties’ aggregate cash interest expense for the applicable period, including interest paid on the Obligations, all capital lease obligations, the Subordinated Debt, and any other Indebtedness for the applicable period; provided, however, that the following amounts will be excluded for purposes only of determining Fixed Charges, that the portion of the ICS Debt, the Sandler Debt, and the Subordinated Debt which is repaid, with Lender’s prior consent, solely from the net cash proceeds received from the exercise of certain warrants issued Parent. The term “applicable period” in this definition means Test Period in the case of determining the Fixed Charge Coverage Ratio or the Maximum Total Funded Debt to Adjusted EBITDA Ratio and Fiscal Year in the case of determining Excess Cash Flow.

“Letter of Credit Availability” means, as at any time, an amount equal to the lesser of (a) an amount equal to (i) $5,000,000 less (ii) the then Letter of Credit Exposure and (b) the then Revolving Loan Availability.

“Loans” means the Revolving Loans (including the Letter of Credit Exposure), Term Loan C and any other loans or other extensions of credit or financial accommodations from time to time from Lender or its Affiliates to any one or more of Borrowers.

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“Loan Party” and “Loan Parties” mean each of Borrowers, Group, Parent, FKI, LLC, and CECO Mexico LLC and collectively, Borrowers, Group, Parent, FKI, LLC and CECO Mexico LLC, respectively.

“Notes” means the Revolving Note (as defined in Section 2.1), Term Loan Note C (as defined in Section 2.2) and any other promissory note made from time to time by a Borrower in favor of Lender to evidence any of the Obligations.

“Revolving Commitment” means $30,000,000 subject to Section 2.2(d) and 2.2(e).

“Subordination Agreement” means the Subordination Agreement between the Subordinated Creditor and Lender dated as of the Closing Date, as amended by the First Amendment to Subordination Agreement dated as of the Effective Date (as defined in the Second Amendment) and the Second Amendment to Subordination Agreement dated as of the Effective Date (as defined in the Third Amendment).

“Termination Date” means: (a) with respect to the Line of Credit, the Letter of Credit Obligations and the other Obligations (other than Term Loan C), the earlier of (i) January 31, 2010 and (ii) the date upon which the entire outstanding balance under the Revolving Note shall become due pursuant to the provisions hereof (whether as a result of acceleration by Lender or otherwise); and (b) with respect to Term Loan C, the earliest of (i) January 31, 2010, (ii) the date upon which the entire outstanding balance under Term Loan Note C shall become due pursuant to the provisions hereof (whether as a result of acceleration by Lender or otherwise), and (iii) the date upon which Term Loan C shall be repaid in full.

1.3 Clause (vii) of the definition of “Eligible Accounts” in Section 1.1 of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

(vii) Accounts owing from any single account debtor to the extent, as of any date, that the total amount of such account debtor’s Indebtedness to any one or more Borrowers exceeds 35% of the face amount (less maximum discounts, credits and allowances which may be taken by, or granted to, such account debtor in connection therewith) of the then outstanding Eligible Accounts of such Borrower or Borrowers; provided, however, that for Accounts (which are otherwise eligible) owing from General Motors Corporation, the foregoing percentage is 40%;

1.4 The following definitions in Section 1.1 of the Credit Agreement are hereby deleted: Foreign Affiliate, Term Loan, Term Loan A, Term Loan B, Term Loan Note, Term Loan Note A and Term Loan Note B.

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1.5 Section 2.1(c) of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

(c) On the Effective Date (as defined in the Third Amendment) of the Third Amendment, Borrowers shall execute and deliver to Lender a Third Amended and Restated Revolving Credit Promissory Note in the form of Exhibit 2.1 attached to the Third Amendment (as amended, the “Revolving Note”), dated as of the Effective Date (as defined in the Third Amendment), in the principal amount of the Revolving Commitment, and bearing interest at such rates, and payable upon such terms, as specified in the Revolving Note.

1.6 Section 2.2 of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

2.2 Term Loans /Mandatory Prepayments.

(a) On December 29, 2005, Lender made a loan to Borrowers in an original aggregate amount equal to $3,100,000 (“Term Loan A”). On February 28, 2007, Lender made a loan to Borrowers in an original aggregate amount equal to $5,000,000 (“Term Loan B”). Borrowers repaid in full Term Loan A and Term Loan B. Subject to the terms and conditions of this Agreement and the effectiveness of the Third Amendment, Lender will make an additional term loan to Borrowers in an amount equal to $5,000,000 (“Term Loan C”). No part of Term Loan C may, on the repayment thereof, be redrawn or reborrowed by a Borrower. The entire unpaid principal balance of, and accrued interest on, Term Loan C, if not sooner repaid, will be due and payable on the Termination Date with respect to Term Loan C. Borrowers shall execute and deliver to Lender a Term Promissory Note in the form of Exhibit 2.2 to the Third Amendment (“Term Loan Note C”), dated as of the Effective Date (as defined in the Third Amendment), in the principal amount of $5,000,000, and bearing interest at such rates, and payable upon such terms, as specified in Term Loan Note C. The proceeds of Term Loan C shall be used (i) to consummate the FKI Acquisition and (ii) for general working capital and corporate purposes.

(b) Subject to the terms of Term Loan Note C and this Agreement, Borrowers may prepay Term Loan C in whole or part at any time. Any prepayment of Term Loan C will be applied to the last to mature of the payments required under Term Loan Note C. Except as provided in the preceding sentence, no partial prepayment will change the due dates or the amount of the monthly principal payments otherwise required by Term Loan Note C.

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(c) In addition to the scheduled payments of principal on Term Loan C set forth in Term Loan Note C, the following payments shall be made to, or retained by, Lender and applied as provided in Section 2.2(d):

(i) Within three Business Days after the date of receipt thereof by any Loan Party, an amount equal to 100% of the Net Proceeds from any sale of any asset, including from the sale of the Cincinnati Facility as contemplated by Section 5.7 (exclusive of (A) sales of Inventory in the ordinary course of business or (B) sales or other dispositions of Equipment, the proceeds of which are used for the replacement of such Equipment as contemplated by Section 5.7);

(ii) Within three Business Days after the date of receipt thereof by any Loan Party, 100% of the Net Proceeds from any insurance or condemnation proceeds payable in respect of, or arising out of, any loss or damage to any of any Borrower’s properties (other than (A) dispositions of Equipment, which is the subject of an Event of Loss, in connection with the replacement of such Equipment as contemplated by Section 5.7 or (B) repairs or replacements of any Mortgaged Property, which is the subject of an Event of Loss, to the extent set forth in the Mortgages); and

(iii) On the date of receipt thereof by any Loan Party, an amount equal to 100% of the Net Proceeds payable or owing to any Loan Party under, or arising out of, the Effox Acquisition Agreement, the Effox Acquisition, the FKI Acquisition Agreement or the FKI Acquisition, including any purchase price adjustment payment or indemnification or reimbursement payment made after the Effective Date (as defined in the Third Amendment) with respect to the Effox Acquisition or the FKI Acquisition. Notwithstanding anything to the contrary in this clause (iii), if a Loan Party incurs any out-of-pocket cost or expense for which it receives reimbursement from Effox under the Effox Acquisition Agreement (“Out-of-Pocket Effox Reimbursement”) or from FKI under the FKI Acquisition Agreement (“Out-of-Pocket FKI Reimbursement”), then the Loan Parties will (A) apply such Out-of-Pocket Effox Reimbursement or Out-of-Pocket FKI Reimbursement, as applicable, against the then outstanding Revolving Loans and (B) not be obligated to apply such Out-of-Pocket Effox Reimbursement or Out-of-Pocket FKI Reimbursement, as applicable, as a mandatory prepayment of Term Loan C.

(iv) Beginning on May 1, 2009 and continuing on the same date thereafter occurring in each subsequent Fiscal Year until the payment in full of Term Loan C, Borrowers will make a payment to Lender in an aggregate amount equal to 50% of Excess Cash Flow for the immediately preceding Fiscal Year of Borrowers

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then ended (each, an “Excess Cash Flow Payment”); provided that Lender will not require an Excess Cash Flow Payment, in any Fiscal Year, in an aggregate amount greater than $1,000,000, but Borrowers may make a voluntary prepayment of Term Loan C in excess of such $1,000,000. Each Excess Cash Flow Payment shall, absent the occurrence and continuance of an Event of Default, be applied to the remaining installments of principal under Term Loan Note C, in the inverse order of maturity.

(d) With respect to mandatory prepayments described in Sections 2.2(c)(i) through 2.2(c)(iv), such prepayments shall, absent the occurrence and continuance of an Event of Default: (i) first, be applied to the remaining installments of principal under Term Loan C, in the inverse order of maturity, until Term Loan C has been paid in full, (ii) second, at any time after the Term Loan C shall have been repaid in full, such payments shall be applied to the outstanding balance of the Revolving Loans, (iii) third, after the Revolving Loans have been paid in full, such payments shall be applied to cash collateralize outstanding Letter of Credit Obligations, and (iv) fourth, after all Letter of Credit Obligations are fully cash collateralized, in repayment of any of the other Obligations then due and payable, and the Revolving Commitment will, at Lender’s sole option, be contemporaneously reduced by an amount deemed appropriate by Lender in the exercise of its discretion in good faith. Nothing in this Section 2.2 shall be construed to constitute Lender’s consent to any transaction that is not permitted by other provisions of this Agreement or the other Loan Documents. No partial prepayment under Section 2.2(c) will change the due dates or the amount of the monthly principal payments otherwise required by Term Loan Note C.

(e) Within three Business Days after the date of receipt thereof by any Loan Party, the Loan Parties shall deliver to Lender: (i) 100% of the Net Proceeds payable under any Life Insurance, including any death benefit, (ii) an amount equal to 100% of: (A) any Net Proceeds from the issuance by Parent of any Ownership Interests after the Closing Date or (B) any dividend or distribution to a Loan Party from a Person other than a Loan Party, or (iii) 100% of the Net Proceeds from any Tax Refund. Such amounts shall, in each case, be applied by Lender to the Obligations as follows: (1) first, to the outstanding balance of the Revolving Loans, (2) second, after the Revolving Loans have been paid in full, such payments shall be applied to cash collateralize outstanding Letter of Credit Obligations, and (3) third, after all Letter of Credit Obligations are fully cash collateralized, in repayment of any of the other Obligations (other than Term Loan C absent the existence and continuation of an Event of Default) then due and payable, and the Revolving Commitment will, at Lender’s sole option, be contemporaneously reduced by an amount deemed appropriate by Lender in the exercise of its discretion in good faith.

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1.7 Section 2 of the Credit Agreement is hereby amended by deleting Section 2.12 in its entirety.

1.8 Section 5.3 of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

5.3 Capital Expenditures. No Loan Party will make or incur any expenditures for real estate, plant, machinery, equipment, or other similar expenditure (including all renewals, improvements and replacements thereto, and all obligations under any lease of any of the foregoing) that would be capitalized on the balance sheet of a Loan Party in accordance with GAAP in excess of (a) $750,000 for the Fiscal Year ending on December 31, 2006, (b) $2,000,000 for the Fiscal Year ending on December 31, 2007, or (c) $2,500,000 for any Fiscal Year ending on or after December 31, 2008; provided that (i) (a) the Purchase Price (as defined in the Effox Acquisition Agreement) paid by any Loan Party in accordance with the Effox Acquisition Agreement and (b) the Purchase Price (as defined in the FKI Acquisition Agreement) paid by any Loan Party in accordance with the FKI Acquisition Agreement, will each be excluded from the foregoing limitation on capital expenditures and (ii) if (A) the Cincinnati Facility is sold and (B) Lender, pursuant to an amendment of this Agreement executed by it, consents to the re-investment of the Net Proceeds from the sale of the Cincinnati Facility into a replacement facility, which becomes a Borrower’s Facility under terms and conditions acceptable to Lender, then the amount of such Net Proceeds used for such replacement facility will be excluded from the foregoing limitation on capital expenditures (the amounts excluded from the foregoing limitation on capital expenditures in clauses (i) and (ii) of this proviso being “Excluded Capital Expenditures”).

1.9 The reference to “Term Loans” in Section 5.7(c)(iii) of the Credit Agreement is hereby amended by substituting a reference to “Term Loan C” for the “Term Loans” where it appears therein.

1.10 Section 5.8 of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

5.8 Transactions with Affiliates. No Loan Party shall: (a) directly or indirectly make any loans or advances to, or investments in, any of its employees, officers, directors, shareholders or other Affiliates except (i) as permitted by Section 5.9 and (ii) in respect of purchases by a Borrower or of another Borrower’s Inventory in the ordinary course of business pursuant to the reasonable requirements of a Borrower’s business and on fair and reasonable terms which are fully disclosed to Lender; (b) enter into any transaction with any of its Affiliates except for such transactions (other than

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transactions contemplated by clause (a) of this Section 5.8) entered into in the ordinary course of business upon fair and commercially reasonable terms no less favorable to such Loan Party than could be obtained in a comparable arms-length transaction with an unaffiliated Person; provided that, a Borrower shall not sell any goods to, or perform any services for or on behalf of, CECO India, Fisher Klosterman Shanghai, CECO Environmental Mexico, or CECO Environmental Services during any time that (i) the total Indebtedness of CECO India and (exclusive of loans, advances or equity investments permitted by Section 5.9(E)) CECO Environmental Mexico, CECO Environmental Services and Fisher Klosterman Shanghai, to Borrowers, in the aggregate exceeds $500,000 or (ii) the total amount of Indebtedness of CECO India and (exclusive of loans, advances or equity investments permitted by Section 5.9(E)) CECO Environmental Mexico, CECO Environmental Services and Fisher Klosterman Shanghai to Borrowers, in the aggregate, and that is past due, exceeds $500,000, or (c) divert (or permit anyone to divert) any of its business opportunities to any Affiliate (other than a Borrower to another Borrower) or any other Person in which any Loan Party or its shareholders holds a direct or indirect interest.

1.11 Section 5.9(a) of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

(a) No Loan Party shall, without Lender’s prior consent (which consent Lender, in good faith, shall have no obligation to provide), purchase or otherwise acquire: (i) all or substantially all of the assets of any Person or the assets comprising any line of business or business unit or division, (ii) any partnership, joint venture or limited liability company interest in or with any Person, or (iii) the securities of, create, form or invest in any Person (including a Subsidiary), or hold beneficially evidences of Indebtedness of, or make any investment or acquire any interest in, or make any advance or loan to, or assume any liability on behalf of, any other Person other than:

(A) as expressly provided in this Agreement;

(B) advances to officers and employees with respect to expenses incurred by those officer and employees, which expenses are (1) in the usual and ordinary course of business of a Borrower, (2) reimbursable by a Borrower, and (3) do not exceed in the aggregate, $50,000, outstanding at any one time;

(C) Loans by one Borrower to, and held by, another Borrower that is unsecured and subordinated in right of payment to the Obligations. Anything to the contrary in this Agreement or the other Loan Documents notwithstanding, no Borrower may receive Revolving Loans from Lender or loans or advances from any other Borrower (each, a “Senior or Intercompany Advance” and collectively, “Senior or Intercompany Advances”) if, when taking into account on a pro forma basis the proposed Senior or Intercompany Advance, the applicable Borrower would have Loans (either directly from Lender or indirectly from another Borrower) that exceed the sum of (1) one hundred ten percent (110%) of the book value of such Borrower’s accounts receivable and inventory and (2) one hundred twenty five percent (125%) of the net book value of such Borrower’s owned Equipment and real property;

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(D) short term investments of excess working capital in one or more of the following so long as no Revolving Loans are then outstanding: (1) investments (of one year or less) in direct or guaranteed obligations of the United States, or any agencies thereof; and (2) investments (of one year or less) in certificates of deposit of banks or trust companies organized under the laws of the United States or any jurisdiction thereof, provided that such banks or trust companies are insured by the Federal Deposit Insurance Corporation and have capital in excess of $250,000,000; and

(E) loans, advances or equity investments in Fisher Klosterman Shanghai, CECO Environmental Mexico and CECO Environmental Services (other than transactions contemplated by clause (b) of Section 5.8), so long as (1) the aggregate amount of such investments does not exceed $500,000 during the term of this Agreement, (2) no Event of Default shall exist at the time of making each such investment, (3) no Event of Default shall result, on a pro forma basis, from the making of each such investment, and (4) after the making of each such investment, Revolving Loan Availability is equal to or greater than $1,000,000. To determine whether there is pro forma compliance with the Financial Covenants, Borrowers will, on a pro forma basis, (x) restate the financial statements received by Lender for the Fiscal Quarter or the Fiscal Year, as applicable, ended most closely before the date such investment is proposed to be made as if the proposed investment had been made at the beginning of the applicable Test Period and (y) calculate the Financial Covenants taking into account such proposed investment as if the proposed investment had been made at the beginning of the applicable Test Period. Borrowers will deliver such pro forma analysis to Lender at least 10 Business Days prior to making each such investment.

1.12 Section 5 of the Credit Agreement is hereby amended by the addition of a new Section 5.13, in its proper numerical order, to provide in its entirety as follows:

5.13 FKI Acquisition; FKI Acquisition Documents. The Loan Parties will not seek, agree to or permit, directly or indirectly, the amendment, waiver or other change to any material term of or applicable to any of the FKI Acquisition Documents. For purposes of this Section 5.13, “material” means any modification, waiver, or amendment of any of the FKI Acquisition Documents, which, in the judgment of Lender exercised in good faith, could: (i) materially increase the purchase price for the assets to be acquired under the FKI Acquisition Documents or the Indebtedness to be incurred by any Loan Party under the FKI Acquisition Documents, (ii) materially and adversely affect any of Lender’s rights or remedies under the Loan Documents, the value of the Loan Collateral, or Lender’s security interest in or other Lien on the Loan Collateral (including the priority of Lender’s interests), (iii) have a Material Adverse Effect, or (iv) create or result in an Event of Default.

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1.13 Section 5 of the Credit Agreement is hereby amended by the addition of a new Section 5.14 and a new Section 5.15, in their proper numerical order, to provide in their entirety as follows:

5.14 FKI, LLC. Notwithstanding anything to the contrary set forth in this Agreement, FKI, LLC (A) is, and will remain, a holding company, whose only business will be the holding of the ownership interest of Fisher Klosterman Shanghai, (B) does not, and will not, have any Indebtedness except the Obligations, and (C) will not own or have any interest in property other than the Ownership Interests of Fisher Klosterman Shanghai, and the distributions received from Fisher Klosterman Shanghai on such Ownership Interests.

5.15 CECO Mexico, LLC. Notwithstanding anything to the contrary set forth in this Agreement, CECO Mexico LLC (A) is, and will remain, a holding company, whose only business will be the holding of the ownership interest of CECO Environmental Services and CECO Environmental Mexico, (B) does not, and will not, have any Indebtedness except the Obligations, and (C) will not own or have any interest in property other than the Ownership Interests of CECO Environmental Services and CECO Environmental Mexico, and the distributions received from CECO Environmental Services and CECO Environmental Mexico on such Ownership Interests.

1.14 Section 6.1(t) of the Credit Agreement is hereby amended in its entirety by substituting the following in its place:

(t)(i) there is a default or an event of default under any of the Effox Acquisition Documents by any Person which has a Material Adverse Effect; or (ii) there is a default or an event of default under any of the FKI Acquisition Documents by any Person which has a Material Adverse Effect.

1.15 Exhibit 2.1 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Exhibit 2.1 in its stead. Exhibit 2.2 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Exhibit 2.2 in its stead. Exhibit 4.3(d) to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Exhibit 4.3(d) in its stead. Exhibit 4.3(g) to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Exhibit 4.3(g) in its stead. Schedule 1.1 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Schedule 1.1 in its stead. Schedule 3.1 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Schedule 3.1 in its stead. Schedule 3.12 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Schedule 3.12 in its stead. Schedule 3.14 to the Credit Agreement is hereby amended in its entirety by substituting the document attached hereto as Schedule 3.14 in its stead.

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2. Consent by Lender to FKI Acquisition. The Loan Parties have requested that Lender consent to the acquisition by FKI Acquisition of substantially all of the assets of FKI and the recognition of FKI Acquisition as a Domestic Subsidiary of Group (collectively, the “FKI Acquisition”), as required by Section 5.9(a) of the Credit Agreement. Subject to the terms, and on the conditions, of this Amendment, Lender hereby consents to the FKI Acquisition. The consent provided in this Section 2, either alone or together with other consents which Lender may give from time to time, shall not, by course of dealing, implication or otherwise, obligate Lender to consent to any other creation, formation, purchase or other acquisition of a Domestic Subsidiary of any Loan Party, past, present or future, other than the FKI Acquisition specifically consented to by this Amendment, or reduce, restrict or in any way affect the discretion of Lender in considering any future consent requested by the Loan Parties.

3. Other Documents. As a condition of this Amendment, Borrowers, with the signing of this Amendment, will deliver or, as applicable, shall cause to be delivered to Lender: (a) the Third Amended and Restated Revolving Credit Promissory Note (“Amended and Restated Revolving Note”) in the form of Exhibit 2.1 attached hereto; (b) the Term Promissory Note (“Term Loan Note C”) in the form of Exhibit 2.2 attached hereto (c) the Joinder Agreement, the Security Agreement, and the Guaranty, each executed by GMD and FKI Acquisition and, with respect to the Guaranty, FKI, LLC and CECO Mexico LLC, each in the forms of Exhibit 3 attached hereto; (d) amendments to each Mortgage in form and substance satisfactory to Lender; (e) the Third Amendment to Pledge Agreement executed by Group in form and substance satisfactory to Lender; (f) copies, certified by the directors of each Borrower, of resolutions of such directors authorizing the execution of this Amendment and all other documents executed in connection herewith, which certificates and resolutions will be in form and substance satisfactory to Lender; (g) the Second Amendment to Subordination Agreement executed by Green Diamond, in form and substance satisfactory to Lender; (h) a Trademark Security Agreement, Patent Assignment and Security Agreement and Copyright Security Agreement executed by GMD and FKI Acquisition and Lender in the form of Exhibit 3 attached hereto; and (i) such other documents, instruments, and agreements deemed necessary or desirable by Lender to effect the amendments to Borrowers’ credit facilities with Lender contemplated by this Amendment.

4. Representations. To induce Lender to accept this Amendment, the Loan Parties hereby represent and warrant to Lender as follows:

4.1 Each Loan Party has full power and authority to enter into, and to perform its obligations under, this Amendment, the Amended and Restated Revolving Note, Term Loan Note C and the other Loan Documents being amended or entered into in connection herewith, and the execution and delivery of, and the performance of their obligations under and arising out of, this Amendment, the Amended and Restated Revolving Note, Term Loan Note C and the other Loan Documents being amended or entered into in connection herewith, respectively, have been duly authorized by all necessary corporate action.

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4.2 This Amendment, the Amended and Restated Revolving Note, Term Loan Note C, and the other Loan Documents being amended or entered into in connection herewith constitute the legal, valid and binding obligations of each Loan Party, as applicable, enforceable in accordance with their respective terms, except as such enforceability may be limited by bankruptcy, insolvency, reorganization or similar laws affecting creditors’ rights generally.

4.3 The Loan Parties’ representations and warranties contained in the Loan Documents are complete and correct as of the date of this Amendment with the same effect as though such representations and warranties had been made again on and as of the date of this Amendment, subject to those changes as are not prohibited by, or do not constitute Events of Default under, the Credit Agreement.

4.4 No Event of Default has occurred and is continuing.

4.5 As of the closing of the FKI Acquisition:

4.5.1 Each Loan Party has adequate power and authority and has full legal right to enter into each of the FKI Acquisition Documents to which it is a party, and to perform, observe and comply with all of its agreements and obligations under each of the FKI Acquisition Documents.

4.5.2 The execution and delivery by each Loan Party of the FKI Acquisition Documents to which it is a party, the performance by each Loan Party of all of its agreements and obligations under the FKI Acquisition Documents to which it is a party, and the consummation of the FKI Acquisition pursuant to the FKI Acquisition Agreement have been duly authorized by all necessary corporate action on the part of such Loan Party and do not and will not: (i) contravene any provision of such Loan Party’s Certificate/Articles of Incorporation or Bylaws/Code of Regulations; (ii) conflict with, or result in a breach of the terms, conditions or provisions of, or constitute a default under, or result in the creation of any Lien (other than a Permitted Lien) upon any of the property of such Loan Party under, any agreement or instrument to which such Loan Party is a party or by which its assets are bound, except for such violations and/or defaults which could not reasonably be expected to have a Material Adverse Effect; (iii) violate or contravene any provision of any law, rule or regulation or any order or ruling thereunder or any decree, order or judgment of any governmental authority except for such violations and/or defaults which could not reasonably be expected to have a Material Adverse Effect; (iv) require any waivers, consents or approvals by any of the creditors or trustees for creditors of such Loan Party or any other Person except those waivers, consents, or approvals which are obtained as of the Effective Date or which are not required to consummate the FKI Acquisition; or (v) require any Person to make any filing under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, or the rules of the Federal Trade Commission thereunder, to give effect to the Effox Acquisition.

4.5.3 There are no proceedings pending or, to the knowledge of any Loan Party, threatened, against any Loan Party which call into question the validity or enforceability of any of the FKI Acquisition Documents.

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4.5.4 The FKI Acquisition has been consummated in accordance with the terms and conditions of the FKI Acquisition Documents and all applicable laws, and FKI Acquisition became the owner, free and clear of any Liens (except any Permitted Liens) of substantially all of the assets of FKI pursuant to the FKI Acquisition Documents. All consents and approvals of, and filings and permits with, and all other actions in respect of, all governmental authorities required in order to consummate the FKI Acquisition in accordance with the terms and conditions of the FKI Acquisition Documents and all applicable laws have been, or prior to the time required, will have been, obtained, given, filed, taken or waived, and are in full force and effect. All applicable waiting periods with respect thereto have, or prior to the time when required, will have, expired without, in all such cases, any action being taken by any competent authority which restrains, prevents or imposes material adverse conditions upon the consummation of the FKI Acquisition.

4.6 The Subordinated Debt, the Sandler Debt and the ICS Debt have each been paid in full and not Refinanced.

5. Costs and Expenses; Amendment Fee. As a condition of this Amendment, (i) Borrowers will pay to Lender an amendment fee of $20,000, payable in full on the Effective Date; such amendment fee, when paid, will be fully earned and non-refundable under all circumstances, and (ii) Borrowers will promptly on demand pay or reimburse Lender for the costs and expenses incurred by Lender in connection with this Amendment, including, without limitation, reasonable attorneys’ fees.

6. Entire Agreement. This Amendment, together with the other Loan Documents, sets forth the entire agreement of the parties with respect to the subject matter of this Amendment and supersedes all previous understandings, written or oral, in respect of this Amendment and the other Loan Documents.

7. Default. Any default by a Loan Party in the performance of its obligations under this Amendment or the other Loan Documents shall constitute an Event of Default under the Credit Agreement if not cured after any applicable notice and cure period under the Credit Agreement.

8. Continuing Effect of Credit Agreement. Except as expressly amended hereby, all of the provisions of the Credit Agreement are ratified and confirmed and remain in full force and effect.

9. One Agreement; References; Fax Signature. The Credit Agreement, as amended by this Amendment, will be construed as one agreement. Any reference in any of the Loan Documents to: (i) the Credit Agreement will be deemed to be a reference to the Credit Agreement as amended by this Amendment, and (ii) the Revolving Note will be deemed to be a reference to the Amended and Restated Revolving Note. This Amendment and the other Loan Documents may be signed by facsimile signatures or other electronic delivery of an image file reflecting the execution hereof, and, if so signed: (a) may be relied on by each party as if the document were a manually signed original and (b) will be binding on each party for all purposes.

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10. Captions. The headings to the Sections of this Amendment have been inserted for convenience of reference only and shall in no way modify or restrict any provisions hereof or be used to construe any such provisions.

11. Counterparts. This Amendment may be executed in multiple counterparts, each of which shall be an original but all of which together shall constitute one and the same instrument.

12. Governing Law. This Amendment shall be governed by and construed in accordance with the internal laws of the State of Ohio (without regard to Ohio conflicts of law principles).

13. Reaffirmation of Security. Loan Parties and Lender hereby expressly intend that this Amendment shall not in any manner (a) constitute the refinancing, refunding, payment or extinguishment of the Obligations evidenced by the existing Loan Documents; (b) be deemed to evidence a novation of the outstanding balance of the Obligations; or (c) affect, replace, impair, or extinguish the creation, attachment, perfection or priority of the Liens on the Loan Collateral granted pursuant to any Security Document evidencing, governing or creating a Lien on the Loan Collateral. Each Loan Party ratifies and reaffirms any and all grants of Liens to Lender on the Loan Collateral as security for the Obligations, and each Loan Party acknowledges and confirms that the grants of the Liens to Lender on the Loan Collateral: (i) represent continuing Liens on all of the Loan Collateral, (ii) secure all of the Obligations, and (iii) represent valid, first and best Liens on all of the Loan Collateral except to the extent, if any, of any Permitted Liens.

14. Reaffirmation of Guaranties. Each Loan Party hereby: (i) ratifies and reaffirms its Guaranty dated as of December 29, 2005 (or dated as of June 8, 2006 as it respects H.M. White or February 28, 2007 as it respects Effox) made by such Loan Party to Lender and (ii) acknowledges and agrees that no Loan Party is released from its obligations under its respective Guaranty by reason of this Amendment or the other Loan Documents and that the obligations of each Loan Party under its respective Guaranty extend, among other Obligations of Borrowers to Lender, to the Obligations of Borrowers under this Amendment, the Amended and Restated Revolving Note, Term Loan Note C and the other Loan Documents being executed or amended in connection herewith. Without limiting the generality of the foregoing, each Loan Party acknowledges and agrees that all references in any Guaranty to (a) the Credit Agreement or the other Loan Documents shall be deemed to be references to the Credit Agreement or such other Loan Document, as amended by, or amended and restated in connection with, this Amendment and (b) “Borrower” or “Borrowers” shall be deemed to include a reference to GMD and FKI Acquisition, as an additional Borrower under the Credit Agreement.

[Signature Page Follows]

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EXECUTION VERSION

IN WITNESS WHEREOF, the Loan Parties and Lender have executed this Amendment by their duly authorized representatives as of the Effective Date.