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Combustion Air Supply
From Inside Building
From Outside Building
(Direct Vent or
Ducted Combustion Air)
Support of Vent Stack
The weight of the vent stack or chimney must not rest on
the heater vent connection. Support must be provided
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 passes through combustible roofs and
walls.
Vent Terminal Location
NOTE: During winter months check the vent cap and
make sure no blockage occurs from build-up of snow
or ice.
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 damage
or personal injury.
3. Gases may form a white vapor plume in winter. The
plume could obstruct a window view if the termination
is installed near windows.
4. Prevailing winds, in combination with below-freezing
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. (305 mm) above
grade, including 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
appliances shall not terminate over public walkways
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. Where local experience indicates that
condensate is a problem with Category I and III
appliances, this provision shall also apply.
12
Exhaust
Heater Venting
Configuration
Vertical Venting
Horizontal
Through-the-Wall
Venting
Vertical Venting with
Ducted Combustion
Air
Vertical Direct Vent
Horizontal Direct Vent
Table H.
Venting Category Requirements
non-categorized
condensing
Certified Vent Materials
Category
(Must be UL 1738 or ULC S636)
IV
IV
Metallic Vent
(such as AL29-4C), Duravent
PolyPro, ASTM D1785 Sch 40
IV
PVC, ASTM F441 Sch 40 CPVC
IV
IV
8. Locate and guard vent termination to prevent
accidental contact by people or pets.
9. DO NOT terminate vent in window well, stairwell,
alcove, courtyard or other recessed area.
10. Terminate a minimum of 1 ft (0.3 m) above any door,
window, or gravity air intake. Condensate can freeze,
causing ice formations.
11. Locate or guard vent to prevent condensate from
damaging exterior finishes. Use a rust-resistant
sheet metal backing plate against brick or masonry
surfaces.
12. DO NOT extend exposed vent pipe outside of
building beyond the minimum distance required for
the vent termination. Condensate could freeze and
block the vent pipe.
U.S. Installations
Refer to the latest edition of the National Fuel Gas Code.
Vent termination requirements are as follows:
1. Vent must terminate at least 4 ft (1.2 m) below, 4 ft
(1.2 m) horizontally from or 1 ft (0.3 m) above any
door, window or gravity air inlet to the building.
2. The vent must not be less than 7 ft (2.1 m) above
grade when located adjacent to public walkways.
3. Terminate vent at least 3 ft (0.9 m) above any forced
air inlet located within 10 ft (3.0 m).
4. Vent must terminate at least 4 ft (1.2 m) horizontally,
and in no case above or below unless 4 ft (1.2 m)
horizontal distance is maintained, from electric
meters, gas meters, regulators, and relief equipment.
5. Terminate vent at least 6 ft (1.8 m) away from
adjacent walls.
6. DO NOT terminate vent closer than 5 ft (1.5 m) below
roof overhang.
7. The vent terminal requires a 12 in. (305 mm) vent
terminal clearance from the wall.
8. Terminate vent at least 1 ft (0.3 m) above grade,
including normal snow line.
Combustion Air
Inlet Materials
Galvanized Steel
PVC
ABS
CPVC
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