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SBN71-120 thru 85-390, SBD30-150/199 TANK TYPE COMMERCIAL
GAS WATER HEATER SERVICE HANDBOOK
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COMBINING VENTS (MANIFOLDING
When vents are combined, the area of the
combined vent should be equal to area of
the largest single vent, plus 50% of area of
all others joining.
EXAMPLE: To combine two 6” vents with
an 8” vent, the area of a combined vent
should be one half area of two 6 inch vents
(14 + 14) plus area of 8 inch vent (50)
or 78 sq. inches.
Referring to chart: 78 sq. inches requires
a 10” diameter vent.
Vent Size Area in
Square
Inches
Vent Size Area in
Square
Inches
5" 20 10" 79
6" 28 12" 113
7" 38 14" 154
8" 50 16" 201
9" 64 18" 254
COMBINED VENTING
Maximize height from water heater vent connection to first elbow or tee.