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Installation and
Service Manual
13
Input Flue Air Inlet
Btu/hr Size Size*
399,999 6" 6"
500,000 6" 6"
650,000 8" 8"
750,000 8" 8"
990,000 10" 10"
1,260,000 12" 12"
1,440,000 12" 12"
1,800,000 14" 12"
2,070,000 14" 12"
* Minimum diameter for air inlet pipe. Installer may increase diameter one pipe
size for ease of installation, if needed.
Combustion Air Inlet Piping
The sidewall or vertical rooftop DirectAire™ combustion air
supply system has specific vent material and installation
requirements. The air inlet pipe connects directly to the unit to
supply combustion air. In most installations, the combustion air
inlet pipe will be a dedicated system with one air inlet pipe per
unit. You can combine multiple air inlets if the guidelines in
Combined Air Inlet Points, page 15 are followed. The air inlet
pipe will be connected to a combustion air inlet cap as specified
in this section.
For normal installations, this system uses a single-wall pipe to
supply combustion air from outdoors directly to the unit.
In cold climates, use a Type-B double-wall vent pipe or an
insulated single-wall pipe for combustion air. This will help
prevent moisture in the cool incoming air from condensing and
leaking from the inlet pipe.
Length of Air Inlet Pipe
The installed length of air inlet pipe from the unit to the outside air
inlet cap must not exceed 50 equivalent feet (15.2m). Subtract
5 feet (1.5m) of equivalent length for each 90° elbow. Subtract
2.5 feet (0.7m) of equivalent length for each 45° elbow.
Do not exceed the limits for the combustion air inlet piping
lengths.
Sidewall Air Inlet
The sidewall air inlet cap is supplied in the Horizontal
DirectAire™ Vent Kit. Order the kit from the appliance
manufacturer. This sidewall cap supplies combustion air for a
single unit only. See TABLE–D, page 19, for kit numbers.
Locate the unit as close as possible to the sidewall where you will
install the combustion air supply system.
FIG. 14 Sidewall Combustion Air Inlet
TABLE - B
Flue and Air Inlet Pipe Sizes
ƽ WARNING: Locate and install the
combustion air inlet cap correctly. Failure to
do so can allow the discharge of flue products
to be drawn into the combustion process.
This can result in incomplete combustion and
potentially hazardous levels of carbon
monoxide in the flue products. This will cause
operational problems and the spillage of flue
products. Spillage of flue products can cause
personal injury or death due to carbon
monoxide poisoning.