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Combustion
Air Supply
Exhaust
Configuration
Heater Venting
Category
Certified
Materials
Combustion Air
Inlet Material
Vertical Natural
Draft Venting
I “B” Vent
From Inside Building
(Non-Direct Venting)
Horizontal Through-
the-Wall Venting
III
Stainless Steel
(Gas Tight)
Vertical Natural
Draft Venting
I “B” Vent
From Outside Building
(Direct Venting)
Horizontal Through-
the-Wall Venting
III
Stainless Steel
(Gas Tight)
Galvanized Steel
PVC
ABS
CPVC
Support of Vent Stack
The weight of the vent stack or chimney must not rest
on the heater vent connection. Support must be pro-
vided in compliance with applicable codes. The vent
should also be installed to maintain proper clearances
from combustible materials.
Use insulated vent pipe spacers where the vent pass-
es through combustible roofs and walls.
Vent Terminal Location
1. Condensate can freeze on the vent cap. Frozen
condensate on the vent cap can result in a blocked
flue condition.
2. Give special attention to the location of the vent
termination to avoid possibility of property dam-
age or personal injury.
3. Gases may form a white vapor plume in winter.
The plume could obstruct a window view if the ter-
mination is installed near windows.
4. Prevailing winds, in combination with below-freez-
ing temperatures, can cause freezing of
condensate and water/ice build-up on buildings,
plants or roofs.
5. The bottom of the vent terminal and the air intake
shall be located at least 12 in. above grade, includ-
ing normal snow line.
6. Un-insulated single-wall metal vent pipe shall not
be used outdoors in cold climates for venting gas-
fired equipment.
7. Through-the-wall vents for Category II and IV
appliances and non-categorized condensing appli-
ances shall not terminate over public walkways or
over an area where condensate or vapor could
create a nuisance or hazard or could be detrimen-
tal to the operation of regulators, relief valves, or
other equipment. Where local experience indi-
cates that condensate is a problem with Category
I and III appliances, this provision shall also apply.
CAUTION: When condensate traps are installed,
condensate must be routed to an appropriate
container for neutralization before disposal, as
required by local codes.
WARNING: Contact the manufacturer of the vent
material if there is any question about the appliance
categorization and suitability of a vent material for
application on a Category III or IV vent system.
Using improper venting materials can result in
personal injury, death or property damage.
NOTE: During winter months check the vent cap
and make sure no blockage occurs from build-up of
snow or ice.
Table L: Venting Category Requirements