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All horizontal runs of the vent pipe shall have a
minimum rise of 1/4" per foot of length and should be
supported at maximum intervals of 5 feet (for Canada,
3 feet) and at each point where an elbow is used.
For horizontal venting, the total length of 4-inch
diameter pipe shall not exceed 30 feet with up to two
90° elbows and 1 termination vent. For each additional
elbow, reduce the total pipe length by 10 feet. The
minimum length, in either case, is 2 feet with two
elbows ending in a termination vent. For vertical
venting, the lengths described above should be fol-
lowed, with a termination vent at the top. The minimum
length is 5 feet with up to two elbows and a termination
vent.
For sidewall venting, locate the heater as close as
possible to the wall being used. The maximum and
minimum wall thickness is determined by the wall
thimble available from the vent manufacturer. Refer to
the vent manufacturer installation instructions.
Additional requirements when venting through a
sidewall:
1. The vent terminal shall be located at least three feet
above any forced air inlet located within ten feet;
or at least four feet below, four feet horizontally
from, or one foot above any door, window, or
gravity air inlet into any building.
It shall also have a minimum horizontal clearance
of four feet from electric meters, gas meters,
regulator and relief equipment.
2. The vent terminal shall be located not less than
seven feet above grade when it is adjacent to
public walkways.
3. The bottom of the vent terminal shall be located at
least twelve inches above grade or ground, or
normally expected snow accumulation level. The
snow level may be higher on walls exposed to
prevailing winds.
4. Avoid areas where local experience indicates that
condensate drippage may cause problems such
as above planters, patios, or over public walk-
ways, or over an area where condensate or vapor
could create a nuisance or hazard, or could be
detrimental to the operation of regulators, relief
valves, or other equipment.
The gas booster heater may be vented 3 ways:
1. Through the sidewall, or the ceiling, as discussed
previously.
2. Into the exhaust system. (See illustration on page
6) Vent pipe must not penetrate filter.
When the unit is vented into the exhaust system, an
electrical inter-lock must be provided to allow the
flow of gas to the booster heater burner ONLY
when the exhaust system is energized.
3. Free vented into a room or space where other gas
fired equipment is installed, provided that one or
more of the other installed equipment is furnished
with a venting system or other approved means for
removing the vent gases so the aggregate input of
the remaining unvented equipment, including the
booster heater, does not exceed 20 BTU per hour
per cubic foot of volume. The volume of a room or
space directly connected by a doorway, archway or
other opening of comparable size that cannot be
closed, may be included in the calculations. Refer
to the National Fuel Gas Code ANSI Z223.1, NFPA
54.
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