3.4. Vent Pipe Sizing
The maximum length is the combined length of straight horizontal and vertical runs, and the
equivalent straight length of fittings and transition pieces of pipe. The maximum equivalent
lengths and minimum pipe diameters are given below in Table 4 for each heater.
Examples:
1. A 40 foot (12.2 m) length of vent pipe and 1 sharp 90° elbow plus a termination (exit
cone or rain cap) add up to 40 ft. + 10 ft. + 10 ft. = 60 equivalent ft. (18.3 m).
2. A 30 foot (9.1 m) length of vent pipe and 2 sharp 90° elbows plus a termination (exit
cone or rain cap) add up to 30 ft. + (2 x 10 ft.) + 10 ft. = 60 equivalent ft. (15.25 m)
NOTE: The maximum combined pressure drop of the exhaust and intake-air vents is 140
equivalent-feet (42.7 m) for 6” (152 mm) pipe (all models). For the INN 600N using
4” (102 mm) pipe the maximum combined pressure drop of exhaust and intake-air
vents is 80 (24.4 m) equivalent-feet.
3.5. Common Vent Pipe Sizing
IMPORTANT NOTES:
1. AERCO forced draft water heaters are designed for application in common vent systems.
2. Please consult the AERCO factory for all applications utilizing common ducted combustion
air with common breeching of exhausts.
3. AERCO boilers and AERCO water heaters may share common combustion air and
exhaust breeching. Other configurations, not depicted in this guide, are possible. If you
intend to implement any of these options, please contact your local AERCO representative
or the AERCO factory for project specific venting and combustion air configurations and
for design assistance and approval when designing manifolded exhaust vent systems.
Connections to common vent breeching or duct work must be accomplished with a 45° lateral or
boot-tee in the direction of flow in the main breeching. Straight “tees” should not be used to
accomplish these connections. See Figure 11a. Similarly, transition from common horizontal vent
to common vertical vent section with condensate drain should use lateral or boot-tee, as shown
in Figure 13, below.
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