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PREPARING FOR INSTALLATION
WATER VAPOR: A BY-PRODUCT OF UNVENTED ROOM HEATERS
Water vapor is a by-product of gas combustion. An unvented room heater produces
approximately one (1) ounce (30 mL) of water for every 1,000 BTUs (.3 kw) of gas input
per hour. An unvented room heater is recommended as a supplemental heater (a room) rather than a
primary heat source (an entire house). In most supplemental heat
applications, the water vapor does not create a problem. In most applications, the water vapor en-
hances the low humidity atmosphere experienced during cold weather.
The following steps will help ensure that water vapor does not become a problem:
1. Be sure the heater is the proper size for the application, including adequate combustion air and
circulation air.
2. If there is high humidity, a dehumidifier may be used to help lower the water vapor content
of the air.
3. Do not use an unvented room heater as the primary heat source.
AIR FOR COMBUSTION AND VENTILATION
This heater shall not be installed in a room or space unless the required volume of indoor combustion
air is provided by the method described in the Nation Fuel Gas Code, ANSI Z223.1/NFPA 54, the
International Fuel Gas Code, or applicable local codes.
PRODUCING ADEQUATE VENTILATION
All spaces in homes fall into one of the three following ventilation classifications:
1. Unusually Tight Construction
2. Unconfined Space
3. Confined Space
The information on pages 8-10 will help you classify your space and provide adequate ventilation.
Confined and Unconfined Space
A confined space as a space whose volume is less than 50 cu. ft. per 1,000 BTU/hr (4.8 m^3 per kw)
of the aggregate input rating of all appliances installed in that space and an unconfining space as a
space whose volume is not less than 50 cu. ft. per 1,000 BTU/hr (4.8 m^3 per kw) of the aggregate
input rating of all appliances installed in that space. Rooms connecting directly with the space in
which the appliances are installed*, through openings not furnished with doors, are considered a
part of the unconfined space.
This heater shall not be installed in a confined space or unusually tight construction unless provisions
are provided for adequate combustion and ventilation air.
* Adjoining rooms are connecting only if there are doorless passageways or ventilation
grills between them.
Unusually Tight Construction
The air that leaks around doors and windows may provide enough fresh air for combustion and venti-
lation. However, in buildings of unusually tight construction, you must provide additional
fresh air.
Unusually tight construction is defined as construction where:
a) walls and ceilings exposed to the outside atmosphere have a continuous water vapor retarder
with a rating of one perm (6x10-11kg per pa-sec-m2) or less with openings gasketed or sealed
and
b) weather stripping has been added on windows that can be opened and on doors and
c) caulking or sealants are applied to areas such as joints around window and door frames,
between sole plates and floors, between wall-ceiling joints, between wall panels, at
penetrations for plumbing, electrical, and gas lines, and at other openings.
If your home meets all of the three criteria above, you must provide additional fresh air.
See "Ventilation Air From Outdoors" (page 9). If your home does not meet all of the
three criteria above, proceed to "Determining Fresh-Air Flow For Heater Location".
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