Lennox International Inc GWB9-100IH-3 Review: Understanding Combustion Air and Vent Pipe Connections

COMBUSTION AIR AND VENT PIPE

Connections And Termination

Provisions for combustion and ventilation air must be in accordance with section, Air For Combustion and Ventilation, of the National Fuel Gas Code,ANSI 2223.1/ NFPA54, or Sections 8.2, 8.3 or 8.4 of National Gas and Propane Installation Code, CAN/CGA-B 149.1, or applicable provisions of the local building code.

Boilers require dedicated direct vent system. All air for combustion is taken directly from outdoors through combustion air intake pipe. All flue products are discharged to outdoors through vent pipe.

1.See Figure 12 thru Figure 14, Pages 24 and 25 for combustion air and vent pipe roof and sidewall termination. Roof termination is preferred. Combustion air and vent pipes must terminate together in same atmospheric pressure zone as shown.

2.Construction through which vent and air intake pipes may be installed is maximum 24 inches, minimum ¼” thickness.

3.Combustion air and vent pipe fittings must conform to American National Standards Institute (ANSI) standards and American Society for Testing and Materials (ASTM) standards D1784 (schedule-40 CPVC), D1785 (schedule-40 PVC), D2665 (PVC-DWV), D2241 (SDR-21 and SDR-26 PVC), D2661 (ABS-DWV), or F628 (schedule-40 ABS). Pipe cement and primer must conform to ASTM standards D2564 (PVC) or D2235 (ABS).

4.Canada construct all combustion air and vent pipes for this unit of ULC S636 listed schedule-40 CPVC, schedule-40 PVC, PVC-DWV or ABS-DWV pipe and pipe cement. SDR pipe is not approved in Canada.

•First 3 feet (900mm) of venting must be readily available for visual inspection.

•Specified primers and glues of certified vent system must be from single manufacturer, and not intermixed with other manufacturer’s vent system parts.

•Components of the certified system must not be interchanged with other vent systems, or unlisted pipe and/or fittings.

NOTICE

Transition from 2” pipe to 3” pipe must be made in vertical run.

5.Boiler combustion air and vent piping connections are sized for 2” pipe. Any pipe size change (to 3”) must be made outside of boiler casing in vertical run of pipe to allow for proper drainage of vent condensate. Due to potential for flue gas temperatures over 155°F, first five (5) feet of vent pipe must be CPVC, the remain- ing vent pipe can be PVC. If any elbows are employed within the first 5 feet of vent, they must be CPVC too. Two (2) - 30” pieces of 2” CPVC pipe. 2½” piece of 2” CPVC pipe, a 2” CPVC elbow and 2” CPVC pipe coupling are furnished with the boiler.

6.Combustion air and vent piping lengths. Table 5, Page 23. First 5 ft. of vent piping run must be 2” CPVC:

Length of pipe is counted from boiler jacket (air intake pipe) or from vent pipe connector(vent pipe). Termination is not counted toward the “Total Equivalent Length”.

For elbows, reduce maximum vent length as shown:

•2” 90° elbow -1 ½ ft. per elbow.

•3” 90° elbow - 3 ft. per elbow.

Example:

To add two (2) 90° elbows to a 3” pipe for a 75 boiler. Each elbow is 3 ft. per 90 ° elbow for a total of 6 ft..

(1 elbow @ 3 ft. + 1 elbow @ 3 ft. = 6 equivalent ft. of pipe)

Total additional pipe is then subtracted from maximum allowable pipe length to give new maximum length of 106 ft. with two (2), 90° elbows.

“TOTAL EQUIVALENT LENGTH”:

Original 112 ft. max. - 6 equivalent ft. for 2 elbows = new 106 ft. maximum length.

7.Pitch combustion air and vent piping back to boiler at minimum ¼” per ft. (21 mm/m) from intake and vent terminals so all moisture in combustion air and vent piping drains to boiler. Pitch pipes continuously with no sags or low spots where moisture can accumulate and block flow of air or flue gas. Combustion air and vent pipes must be airtight and watertight.

8.Consider following when determining appropriate location for termination of combustion air and vent piping.

•Position termination where vent vapors will not damage plants/shrubs or air conditioning equipment.

•Position termination as to not be effected by wind eddy, air born leaves, snow, or recirculated flue gases.

•Position termination where it will not be subjected to potential damage by foreign objects, such as stones, balls, etc..

•Position termination should where vent vapors are not objectionable.

•Place vent on wall away from prevailing wind. Locate or guard vent to prevent accidental contact with people or pets.

•Terminate vent above normal snowline. Avoid locations where snow may drift and block vent. Ice or snow may cause boiler to shut down if vent becomes obstructed.

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