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Example:
To add 2 additional 90 degree elbows to a 3” pipe for a 75 boiler.
Each elbow is 3 additional feet per 90 degree elbow for a total of 6 feet.
(1 elbow @ 3 feet + 1 elbow @ 3 feet = 6 additional feet of pipe)
e total additional pipe is then subtracted from the maximum allowable pipe length to give the new maximum length of 94
feet with 6, 90 degree elbows.
(“TOTAL EQUIVALENT LENGTH”):
Original 100 feet max. - 6 feet for 2 additional elbows = new 94 feet maximum length.
e rst 5 feet of “TOTAL EQUIVALENT LENGTH” of vent
piping run must be CPVC:
e length of pipe is counted from the boiler jacket (air intake
pipe) or from vent tee (vent pipe) the termination is not
counted toward the “Total Equivalent Length”.
For additional elbows, reduce the maximum vent length as
shown:
•2”90degreeelbow-1½feetperadditionalelbow.
•3”90degreeelbow-3feetperadditionalelbow.
COMBUSTION AIR AND VENT PIPING LENGTHS
BOILER
SIZE
2” PIPE MINIMUM
VENTING
2” PIPE MAXIMUM
VENTING”
3” PIPE MINIMUM
VENTING
3” PIPE MAXIMUM
VENTING”
100 8 FEET 21 FEET 27 FEET 92 FEET
75 & 50 8 FEET 26 FEET 32 FEET 112 FEET
Combustion air and vent piping to be pitched back to boil-
5.
er at minimum ¼” per foot from intake and vent terminals
so that all moisture in combustion air and vent piping
drains to boiler. Pipes must be pitched continuously with
no sags or low spots where moisture can accumulate and
block the ow of air or ue gas. Combustion air and vent
pipes must be airtight and watertight.
Combustion air and vent piping lengths:
4.
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