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AP18733 REV. 3.2.17
36
▪ F. COMMON VENT PIPING
DANGER
Common Vented water heaters must be direct vented, with an exhaust vent and intake air pipe vented to the outdoors. DO NOT power vent
Common Vented water heaters! Doing so will result in property damage, severe personal injury, or death.
These water heaters can be common vented. Connecting several water heaters
together requires proper sizing of the intake and exhaust pipes. Up to eighteen water
heaters can be connected (cascading) together.
1. VENT DIAMETER SIZING AND LENGTHS
These water heaters are designed for 3 inch exhaust vent and intake pipes. The
following chart outlines the maximum length of common venting allowable. A vent
system’s length is calculated by adding the length of all straight pieces used (both
horizontal and vertical) and then adding the equivalent lengths of each tting used in
the system. A vent system’s length must not exceed the maximum length outlined in
the chart below.
NOTE: Reduce the maximum equivalent length above by 5 feet per 90
°
C elbow used and by 2 feet per 45
°
C elbow used. DO NOT exceed the
above set limits.
Maximum Vent Length (in Ft.) for Direct Vent (2 Pipe)
Number
of Water
Heaters
Common
Vented
Load
(BTU/Hr)
Pipe Size
3″ 4″ 6″ 8″ 10″ 12″
1 199,000 100 N/A
N/A N/A N/A N/A
2 398,000 50 83
Table 13 – Maximum Common Vent Length for Direct Vent (2 Pipe)
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