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127029-01D
7
AIR FOR COMBUSTION AND VENTILATION
WARNING: This fi rebox 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 National Fuel Gas Code, ANSI Z223.1/NFPA 54, the
International Fuel Gas Code, or applicable local codes.
Read the following instructions to ensure proper fresh air
for this and other fuel-burning appliances in your home.
Today’s homes are built more energy effi cient than ever. New materials,
increased insulation and new construction methods help reduce heat
loss in homes. Homeowners apply weather strip and caulk around
windows and doors to keep the cold air out and the warm air in. During
heating months, homeowners want their homes as airtight as possible.
While it is good to make your home energy effi cient, your home needs
to breathe. Fresh air must enter your home. All fuel-burning appliances
need fresh air for proper combustion and ventilation.
Exhaust fans, some fi replaces, clothes dryers and some fuel-burning
appliances draw air from the house to operate. You must provide ad-
equate fresh air for these appliances. This will ensure proper venting
of vented fuel-burning appliances.
PROVIDING ADEQUATE VENTILATION
The following are excerpts from National Fuel Gas Code, ANSI Z223.1/
NFPA 54, Air for Combustion and Ventilation.
All spaces in homes fall into one of the three following ventilation
classifi cations:
1. Unusually Tight Construction
2. Unconfi ned Space
3. Confi ned Space
The information on
Pages 7 through 8
will help you classify your space
and provide adequate ventilation.
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.
Unusually tight construction is defi ned as construction where:
a. walls and ceilings exposed to the outside atmosphere have a
continuous water vapor retarder with a rating of one perm (6 x
10
-11
kg per pa-sec-m
2
) 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 fl oors, be-
tween 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 ad-
ditional fresh air. See Ventilation Air From Outdoors,
Page 8
.
If your home does not meet all of the three criteria above, proceed
to Determining Fresh-Air Flow For Firebox Location.
Confi ned and Unconfi ned Space
The National Fuel Gas Code, ANSI Z223.1/ NFPA54 allows two meth-
ods for determining whether the space in which the heater is being
installed is confi ned or unconfi ned space. The standard method
defi nes a confi ned space as a space whose volume is less than 50
cubic feet per 1,000 Btu per hour (4.8 m
3
per kw) of the aggregate
input rating of all appliances installed in that space and an unconfi ned
space as a space whose volume is not less than 50 cubic feet per
1,000 Btu per hour (4.8 m
3
per kw) of the aggregate input rating of all
appliances installed in that space. Rooms communicating directly with
the space in which the appliances are installed*, through openings not
furnished with doors, are considered a part of the unconfi ned space.
Where the air infi ltration rate of a structure is known, the Known Air
Infi ltration Rate Method may be used. Follow The National Fuel Gas
Code, ANSI Z223.1/NFPA 54 to use this method to determine if the
space is confi ned or unconfi ned.
* Adjoining rooms are communicating only if there are doorless
passageways or ventilation grills between them.
DETERMINING FRESH-AIR FLOW FOR FIREBOX LOCATION
Determining if You Have a Confi ned or Unconfi ned Space Using
the Standard Method
Use this work sheet to determine if you have a confi ned or uncon-
fi ned space.
Space: Includes the room in which you will install heater plus any ad-
joining rooms with doorless passageways or ventilation grills between
the rooms.
1. Determine the volume of the space (length x width x height).
Length x Width x Height =__________cu. ft. (volume of space)
Example: Space size 22 ft. (length) x 18 ft. (width) x 8 ft. (ceiling
height) = 3,168 cu. ft. (volume of space)
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. Multiply the space volume by 20 to determine the maximum Btu/Hr
the space can support.
_______ (volume of space) x 20 = (Maximum Btu/Hr the space
can support)
Example: 3,168 cu. ft. (volume of space) x 20 = 63,360 (maximum
Btu/Hr space can support)
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free fi replace ________ Btu/Hr
Gas water heater* ________ Btu/Hr
Gas furnace
________ Btu/Hr
Vented gas heater ________ Btu/Hr
Gas fi replace logs ________ Btu/Hr
Other gas appl _____ Btu/Hr
Total
= _______ Btu/Hr
* Do not include direct-vent gas appliances. Direct-vent draws
combustion air from the outdoors and vents to the outdoors.
Example:
Gas water heater 40,000 Btu/Hr
Vent-free fi r 39,000 Btu/Hr
Total
= 79,000 Btu/Hr
4. Compare the maximum Btu/Hr the space can support with the
actual amount of Btu/Hr used.
______ Btu/Hr (maximum the space can support)
______ Btu/Hr (actual amount of Btu/Hr used)
Example:
63,360 Btu/Hr (maximum the space can support)
79,000 Btu/Hr (actual amount of Btu/Hr used)
