Form #42710000
May 2013
-23-
B.
B.
B.
B.
INDIRECT VENTING (UNVENTED HEATERS)
INDIRECT VENTING (UNVENTED HEATERS)
INDIRECT VENTING (UNVENTED HEATERS)
INDIRECT VENTING (UNVENTED HEATERS) — This heater requires ventilation in the building to dilute the
products of combustion and provide fresh air for efficient combustion. Where unvented heaters are used,
gravity or mechanical means shall be provided to supply and exhaust at least 4 CFM per 1,000 Btu/hr input
of installed heaters. Exhaust vents must be located at the highest point above and in the vicinity of the
heaters, and the inlet vents must be located below the level of the heaters. An exhaust hood (Part
#42924000) must be placed on the outlet collar of the draft inducer or on the existing 4” starting collar
when used unvented and must be mounted only in a
must be mounted only in a
must be mounted only in a
must be mounted only in an
n
n
n upright
upright
upright
upright position
position
position
position and directed t
and directed t
and directed t
and directed towards the reflector
owards the reflector
owards the reflector
owards the reflector
body
body
body
body as shown.
as shown.
as shown.
as shown.
Exhaust Hood
-Required for UNVENTED use-
Draft Inducer
(vertical position)
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 14.0) 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
after first
after first
after first
removing and discarding the perforated cover
removing and discarding the perforated cover
removing and discarding the perforated cover
removing 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.
