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8.15 Outside Combustion Air Supply
IMPORTANT:
If the building has a slight negative pressure or corrosive contaminants such as halogenated
hydrocarbons are present in the air, an outside combustion air supply to the heater is required. Seal all
combustion air pipe joints.
Use of optional outside combustion air is not recommended with unvented heaters.
The air supply duct may have to be insulated to prevent condensation on the outer surface. The outside air
terminal must not be more than 1 ft (31 cm) above the vent termination while maintaining a minimum distance of
3 ft (93 cm) for both vertical and horizontal venting.
8.15.1 Length Requirements
Follow the constraints listed under “8.8 Length Requirements” on page 36.
8.15.2 Vertical Outside Air Supply for Single Heater Installation
Description
Vent Cap, Metalbestos — 4 in. (10 cm)
Vent Cap
Roof
2 ft (0.61 m)
Min.
4 in. (10 cm)
Single Wall Pipe
Flex Hose
(recommended)
Band Clamp
(recommended)
Burner
Summary of Contents for IRH
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