Table of Contents
Advertisement
WATER VAPOR: A BY-PRODUCT OF UNVENTED ROOM HEATERS
Water vapor is a by-product of gas combustion. An unvented room
supplemental heat applications, the water vapor does not create a
problem. In most applications, the water vapor enhances the low
humidity atmosphere experienced during cold weather.
The following steps will help insure that water vapor does not
PROVISIONS FOR ADEQUATE COMBUSTION & VENTILATION AIR
tight construction unless provisions are provided for adequate
combustion and ventilation air.
1,000 Btuh of the combined input rates of all appliances drawing
combustion air from that space. Small areas such as equipment
which supply heated air to areas outside the space must draw return
air from outside the space through tightly sealed return air ducts. A
tion air. One opening must be within 12 inches of the ceiling and
of these openings is determined by whether inside or outside air is
used to support combustion, the method by which the air is brought
of all appliances in the space.
Unusually Tight Construction
The air that leaks around doors and windows may provide enough
fresh air for combustion and ventilation. However, in buildings of
unusually tight construction, you must provide additional fresh air.
a. Walls and ceilings exposed to the outside atmosphere have
a continuous water vapor retarder with a rating of one perm
or less with openings gasketed or sealed, and
b. Weather-stripping has been added on openable windows
and doors, and
c. Caulking or sealants are applied to areas such as joints
around window and door frames, between sole plates and
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
14.
space.
Space: Includes the room in which you will install heater plus any
adjoining rooms with doorless passageways or ventilation grills
between the rooms.
26497-6-0511
become a problem.
1. Be sure the heater is sized properly for the application, including
ample combustion air and circulation air.
help lower the water vapor content of the air.
3. Do not use an unvented room heater as the primary heat
source.
Length x Width x Height =
space)
Example:
If additional ventilation to adjoining room is supplied with grills
or openings, add the volume of these rooms to the total volume
of the space.
2.
Divide the space volume by 50 cubic feet to determine the
maximum BTU/Hr the space can support.
-
BTU/Hr the space can support)
Example:
3. Add the BTU/Hr of all fuel burning appliances in the space.
Vent-free heater
Gas water heater
Gas furnace
Vented gas heater
Other gas appliances*+
Total
Example: Vented gas heater
Vent-free heater
Total
*Do not include direct-vent gas appliances. Direct vent draws
combustion air from the outdoors and vents to the outdoors.
4. Compare the maximum BTU/Hr the space can support with the
actual amount of BTU/Hr used.
Example:
page
Warning: If the area in which the heater may be operated is smaller
unusually tight construction, provide adequate combustion and
ventilation air by one of the methods described in the National
Fuel Gas Code, ANSI Z223.1/NFPA 54, Air for Combustion and
Ventilation, or applicable local codes.
BTU/Hr
BTU/Hr
BTU/Hr
BTU/Hr
BTU/Hr
BTU/Hr
=
BTU/Hr
20,000
BTU/Hr
+ 18,000
BTU/Hr
=
38,000
BTU/Hr
Page 13
Advertisement
Table of Contents
