A FIFTH THIRD BANCORP BANK FOURTH AMENDED AND RESTATED REVOLVING CREDIT PROMISSORY NOTE

Exhibit 10.2

EXECUTION VERSION

A FIFTH THIRD BANCORP BANK

FOURTH AMENDED AND RESTATED

REVOLVING CREDIT PROMISSORY NOTE

December 29, 2005

First Amendment and Restatement June 8, 2006

Second Amendment and Restatement February 28, 2007

Third Amendment and Restatement February 29, 2008

Fourth Amendment and Restatement March 31, 2009

(Effective Date)

Promise to Pay . On or before April 1, 2011 (the “ Maturity Date ”), the undersigned, CECO FILTERS, INC., a Delaware corporation, NEW BUSCH CO., INC., a Delaware corporation, THE KIRK & BLUM MANUFACTURING COMPANY, an Ohio corporation, KBD/TECHNIC, INC., an Indiana corporation, CECOAIRE, INC., a Delaware corporation, CECO ABATEMENT SYSTEMS, INC., a Delaware corporation, H.M. WHITE, INC., a Delaware corporation, EFFOX INC., formerly known as CECO Acquisition Corp., a Delaware corporation, GMD ENVIRONMENTAL TECHNOLOGIES, INC., formerly known as GMD Acquisition Corp., a Delaware corporation, and FISHER-KLOSTERMAN INC., formerly known as FKI Acquisition Corp., a Delaware corporation (each, a “ Borrower ”, and, collectively, the “ Borrowers ”), for value received, hereby jointly and severally promise to pay to the order of FIFTH THIRD BANK, an Ohio banking corporation (together with its successors and assigns, “ Lender ”), at 38 Fountain Square Plaza, MD #10AT63, Cincinnati, Ohio 45263, or such other address as Lender may provide from time to time, the sum of THIRTY MILLION AND 00/100 Dollars ($30,000,000.00), plus interest as provided herein, or so much thereof as is loaned by Lender to Borrowers as Revolving Loans or for which credit is extended by Lender as a Letter of Credit pursuant to the Credit Agreement among Lender, Borrowers, and certain of Borrowers’ affiliates dated as of December 29, 2005, as amended by the First Amendment to Credit Agreement dated as of June 8, 2006, the Second Amendment to Credit Agreement dated as of February 28, 2007, the Third Amendment to Credit Agreement dated as of February 29, 2008, the Fourth Amendment to Credit Agreement dated as of August 1, 2008, the Fifth Amendment to Credit Agreement dated as of December 30, 2008, and the Sixth Amendment to Credit Agreement dated to be effective as of even date herewith (as amended and as the same may be further amended, renewed, consolidated, restated or replaced from time to time, the “ Credit Agreement ”). The outstanding balance of this Fourth Amended and Restated Revolving Credit Promissory Note (this “ Note ”) shall appear on supplemental bank records and is not necessarily the face amount of this Note, which record shall evidence the balance due pursuant to this Note at any time. As used herein, “ Local Time ” means the time at the office of Lender specified in this Note.

This Note, and any request by Borrowers from time to time for an advance of a specified principal amount hereunder, shall be subject to the terms and conditions of the Credit Agreement. Capitalized terms used herein which are not otherwise defined in this Note shall have the meanings set forth in the Credit Agreement. This Note is entitled to the benefits and security of the Credit Agreement, including, without limitation, acceleration upon the terms provided therein, and of the other Loan Documents.

The entire unpaid principal balance of this Note, together with all accrued and unpaid interest and any other charges, advances and fees, if any, outstanding hereunder, shall be due and payable in full on the earlier of the Maturity Date or upon acceleration of the Indebtedness evidenced by this Note, notwithstanding any other inconsistent or contradictory provisions contained in this Note.

Upon the occurrence and during the continuance of any Event of Default, the entire unpaid principal balance of this Note, together with all accrued but unpaid interest, and all other Obligations, shall, at Lender’s option, become immediately due and payable, except that if there occurs an Event of Default of the type described in Sections 6.1(d) , 6.1(e) , or 6.1(j) of the Credit Agreement, the entire unpaid principal balance of this Note, together with all accrued but unpaid interest, and all other Obligations shall become automatically and immediately due and payable without notice, which Borrowers hereby waive.

Interest . Principal amounts outstanding under this Note shall bear interest commencing on the Signature Date (as defined in the Sixth Amendment) at the rate or rates per annum set forth below, which rate or rates shall be designated by Borrowers as more fully set forth herein (the “ Interest Rate ”). Notwithstanding anything to the contrary in this Note or any other Loan Document, principal amounts outstanding under this Note shall bear interest during the period commencing on the Effective Date through, and including, the date that is the day prior to the Signature Date (as defined in the Sixth Amendment) at the rate or rates per annum set forth in the Prior Note.

On and after the Signature Date, at any time and from time to time during the term of this Note, so long as no Event of Default has occurred and is continuing and so long as such outstanding principal amounts hereunder are not then subject to a LIBOR Tranche Election, Borrowers may exercise their right to adjust the Interest Rate on amounts of principal outstanding under this Note to one of the rates set forth below upon notice to Lender as set forth below; provided, however , that once the Interest Rate accruing against any amounts outstanding hereunder is adjusted to a Tranche LIBOR Rate for a particular LIBOR Tranche Interest Period, Borrowers may not elect to adjust such Interest Rate to a different Interest Rate until the expiration of such LIBOR Tranche Interest Period.

(a) Tranche LIBOR Rate . Upon telephonic notice to Lender by 10:00 a.m. Local Time given at least two Business Days prior to the beginning of a LIBOR Tranche Interest Period, Borrowers may, subject to the terms of this Note, elect to have advances under this Note bear interest at a rate per annum equal to the Tranche LIBOR Rate (as defined herein) plus the Applicable Tranche LIBOR Rate Margin (as defined herein) (a “ LIBOR Tranche Election ”). The “ Tranche LIBOR Rate ” is the rate of interest (rounded upwards, if necessary, to the next  ¹ / 8 of 1% and adjusted for reserves if Lender is required to maintain reserves with respect to relevant advances) fixed by the British Bankers’ Association at 11:00 a.m., London, England time, relating to quotations for the one month, two month, or three month London InterBank Offered Rates, as selected by Borrowers in their LIBOR Tranche Election, on U.S. Dollar deposits as published on Bloomberg LP, or, if no longer provided by Bloomberg LP, such rate as shall be determined in good faith by Lender

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from such sources as Lender shall determine to be comparable to Bloomberg LP (or any successor) as determined by Lender at approximately 10:00 a.m. Local Time on the date of request by Borrowers. Each determination by Lender of the Tranche LIBOR Rate shall be conclusive in the absence of manifest error. Interest accruing based on the Tranche LIBOR Rate shall be: (i) calculated based on a 360-day year and charged for the actual number of days elapsed and (ii) payable in arrears on the last day of the applicable LIBOR Tranche Interest Period. The Interest Rate applicable to a particular LIBOR Tranche Election shall remain at the rate elected for the remainder of the subject LIBOR Tranche Interest Period.

The “ LIBOR Tranche Interest Period ” for each advance bearing interest with respect to the Tranche LIBOR Rate (each such advance, a “ Tranche LIBOR Rate Loan ”) is a period of one month, two months, or three months, at Borrowers’ election, which period shall commence on a Business Day selected by Borrowers subject to the terms of this Note. If a LIBOR Tranche Interest Period would otherwise end on a day that is not a Business Day, such LIBOR Tranche Interest Period shall end on the next succeeding Business Day; provided that, if the next succeeding Business Day falls in a new month, such LIBOR Tranche Interest Period shall end on the immediately preceding Business Day.

On or before the date that is two Business Days before the making of any Tranche LIBOR Rate Loan, and on or before the date which is two Business Days prior to the expiration of any applicable LIBOR Tranche Interest Period, Borrowers shall notify Lender of each of the following: (a) the LIBOR Tranche Interest Period Borrowers have elected regarding any such Tranche LIBOR Rate Loan or any continuation of a LIBOR Tranche Election with respect to a Tranche LIBOR Rate Loan, (b) the amount of each such Tranche LIBOR Rate Loan or continuation, and (c) the commencement date of each LIBOR Tranche Interest Period. Borrowers may have Tranche LIBOR Rate Loans in minimum amounts of $1,000,000 (and integral multiples of $100,000) and such Tranche LIBOR Rate Loans may bear interest at the applicable Interest Rate for different LIBOR Tranche Interest Periods so long as (i) the last day of any LIBOR Tranche Interest Period does not exceed the Maturity Date hereof; (ii) no LIBOR Tranche Election with respect to any Tranche LIBOR Rate Loan commences prior to the expiration of the applicable LIBOR Tranche Interest Period in effect with respect to such Tranche LIBOR Rate Loan; and (iii) at no time may Borrowers have more than three outstanding Tranche LIBOR Rate Loans, in the aggregate, under all of their Notes. If, at any time during the term hereof, Borrowers fail to designate a LIBOR Tranche Interest Period or if Borrowers have not elected another LIBOR Tranche Interest Period in accordance with this Note at least two Business Days prior to the expiration of the LIBOR Tranche Interest Period then in effect, Lender may assume that Borrowers have elected to have the principal amount applicable to such expiring LIBOR Tranche Interest Period accrue interest based on the Daily LIBOR Rate.

(b) Daily LIBOR Rate . All amounts outstanding under this Note, as of any date, which are not then subject to a LIBOR Tranche Election, will automatically bear interest at a floating rate equal to the Daily LIBOR Rate plus the Applicable Daily LIBOR Rate Margin (as defined below). As used herein, “ Daily LIBOR Rate ” means the rate of interest (rounded upwards, if necessary, to the next  ¹ / 8 of 1% and adjusted for reserves if Lender is required to maintain reserves with respect to relevant advances) fixed by the British Bankers’ Association at 11:00 a.m., London, England time, relating to quotations for the one month London InterBank Offered Rate on U.S. Dollar deposits as published on Bloomberg LP, or, if no longer provided by Bloomberg LP, such rate as shall be determined in good faith by Lender from such sources as Lender shall determine to be comparable to Bloomberg LP (or any

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successor) as determined by Lender at approximately 10:00 a.m. Local Time on the relevant date of determination. Each determination by Lender of the Daily LIBOR Rate shall be conclusive in the absence of manifest error. The Daily LIBOR Rate shall be reset each Business Day by Lender based on the Daily LIBOR Rate then in effect. Any adjustment in the Interest Rate resulting from a change in the Daily LIBOR Rate shall become effective as of the opening of business on the date of each change (or if not a Business Day, the beginning of the day). Lender shall not be required to notify Borrowers of any adjustment in the Daily LIBOR Rate; however, Borrowers may request a quote of the prevailing Daily LIBOR Rate on any Business Day. Interest accruing based on the Daily LIBOR Rate shall be: (i) calculated based on a 360-day year and charged for the actual number of days elapsed and (ii) payable in arrears on the first day of each calendar month.

(c) Pricing Grid . As used herein, the terms “ Applicable Daily LIBOR Rate Margin ” and “ Applicable Tranche LIBOR Rate Margin ” (hereafter sometimes collectively referred to as the “ Applicable Margins ”) mean, as of any date, the applicable per annum rate shown in the applicable column in the table below based on the then applicable Fixed Charge Coverage Ratio. “ Fixed Charge Coverage Ratio ” has the meaning given in the Credit Agreement.