Form 43471030
-24-
Sept 2011
15.0)
AIR FOR COMBUSTION
If indoor combustion air is to be supplied for a tightly enclosed area, one square inch of free area opening shall
be provided below the heater for each 1,000 Btu/hr per hour of heater input. When outside air is used, the
opening below the heater shall be one square inch of free area for each 4,000 Btu/hr of heater input. In
contaminated atmospheres or high humidity areas, optional outside air for combustion is recommended.
Adequate clearances around the perforated fresh air plate must be maintained at all times. In larger open areas
of buildings, infiltration normally is adequate to provide air for combustion.
15.1)
DIRECT OUTSIDE AIR FOR COMBUSTION
Outside combustion air should be supplied directly to the heater when the building is subject to negative
pressure, or when contaminants or high humidity are present in the building air. These contaminants include
paints, solvents, corrosive vapors or any other foreign particles that may cause damage to the heater or result in
poor combustion.
Outside combustion air can be brought directly to the heater by a 4” diameter duct less than 50 ft. long or
equivalent (see table in Section C based on selected model and heat exchanger lengths). This is attached to the
4” diameter starting collar. The starting collar is fitted to the top of the control box cabinet after first removing
after first removing
after first removing
after first removing
and discarding the perforated cover
and discarding the perforated cover
and discarding the perforated cover
and discarding the perforated cover. An approved vent cap must be placed directly on the end of the outside
combustion air inlet pipe. The combustion air inlet should be not less than 3 ft. (0.9m), either vertically or
horizontally, from the flue vent termination. The air intake terminal must be located not less than 1 ft. (30cm)
above grade. It is good installation practice to supply combustion air from the same pressure zone as the vent
outlet. Avoid bringing combustion air to the heater from an attic space. There is no guarantee that adequate
combustion air will be supplied.
In colder climates, where necessary, insulate the outside combustion air duct. Avoid locating the outside
combustion air duct directly above the control box. Provide a capped cleanout T as necessary. In high humidity
applications, the control box should be sealed with silicone sealer.
In multiple heate
multiple heate
multiple heate
multiple heater applications
r applications
r applications
r applications, the combustion air intake may be ducted individually or common ducted in the
same configuration as shown for venting in Section C. For combustion air intake duct sizing, please refer to the
Vent Sizing Table
Vent Sizing Table
Vent Sizing Table
Vent Sizing Table and use the diameter indicated, based on the number of heaters per duct.
Flue vent termination
must be 1 ft. (30cm)
higher than combustion
air inlet cap
Perforated Cover
(Remove)
The combustion air inlet should
be not less than 3 ft. (0.9m),
either vertically or horizontally,
from the flue vent termination.
