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GAS-FIRED BOILER Boiler Manual
PART 7: VENTING, COMBUSTION AIR & CONDENSATE REMOVAL
(CONTINUED)
E. EXHAUST VENT AND INTAKE AIR VENT
SIZING
1. The exhaust vent and intake air vent pipes
should be 2" for the T50/T80, 3" for the
80M/140M/199M and 4" for the 399M.
2. The total combined equivalent length of
exhaust vent and intake air pipe should not
exceed 85 feet.
a. The equivalent length of elbows, tees,
and other fittings are listed in the Friction
Loss Table 7.5.
*Friction loss for long radius elbow is 1 foot less.
b. For example: If the exhaust vent has two
90° elbows and 10 feet of PVC pipe we
will calculate:
Exhaust Vent Pipe Equivalent Length = (2x5)+10=20 feet
Further, if the intake air vent pipe has two
90° elbows, one 45° elbow and 10 feet of
PVC pipe, the following calculation
applies:
Intake Air Vent Pipe Equivalent Length = (2x5)+3+10=23 feet
Finally, if a concentric vent kit is used we
find:
Total Combined Equivalent Length = 20+23+3=46 feet
Therefore, the total combined equivalent
length is 46 feet which is well below the
maximum of 85 feet.
c. The intake air vent pipe and the exhaust
vent are intended to penetrate the same
wall or roof of the building.
d. Effort should be made to keep a
minimum difference in equivalent length
between the intake air vent pipe and the
exhaust vent.
3. The minimum combined equivalent length is
16 equivalent feet.
F. LONGER VENT RUNS
1. The maximum combined equivalent length
can be extended by increasing the diameter
of both exhaust vent and intake air vent pipe
equally. However, the transitions should
begin a minimum of 15 equivalent feet from
the boiler.
a. The maximum equivalent length for the
increased diameter vent pipes is 125 feet.
b. Transitions should always be made in
vertical sections of pipe to prevent the
condensate from pooling in the vent
pipe.
c. If the transition occurs at a distance
greater than 15 equivalent feet from the
boiler, the maximum equivalent length
will be reduced. See Table 7.7.
G. EXHAUST VENT AND INTAKE AIR PIPE
INSTALLATION
1. Use only solid PVC, CPVC, or ABS schedule
FRICTION LOSS EQUIVALENT IN PIPING AND FITTINGS
FITTINGS OR PIPING EQUIVALENT FEET
2" 3" 4"
6"
90 DEGREE ELBOW* 5' 5' 3'
3'
45 DEGREE ELBOW 3' 3' 1'
1'
COUPLING 0' 0' 0'
0'
AIR INLET TEE 0' 0' 0'
0'
STRAIGHT PIPE 1' 1' 1'
1'
CONCENTRIC VENT KIT 3' 3' N/A
N/A
V500 2" VENT KIT 1' N/A N/A
N/A
V1000 3" VENT KIT N/A 1' 1'
1'
V2000 4" VENT KIT N/A 1' 1' 1'
Table 7.5
Transition
Point
(ft from
boiler)
TEL of
Standard
2" Vent
Pipe (ft)
TEL of
Oversized
2", 3" or 4"
Vent Pipe (ft)
Maximum
TEL of all
Vent Pipe (ft)
15 30 95 125
20 40 77-1/2 117-1/2
25 50 60-1/2 110-1/2
30 60 43 103
35 70 26 96
40 80 8-1/2 88-1/2
None 85 0 85
Vent
Connection
Reducing
Coupling
Vent
Transition
2" 3" x 2" 3"
3" 4" x 3" 4"
4" 6" x 4" 6"
TEL = Total Equivalent Length
Table 7.7: Vent Termination Kits
Table 7.6: Vent Run Transition