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Confined and Unconfined 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 confined or unconfined space. The standard method is
a space whose volume is less than 50 cubic feet per 1,000 Btu per
hour (4.8 m3per kw) of the aggregate input rating of all appliances
installed in that space and an unconfined space as a space whose
volume is not less than 50 cubic feet per 1,000 Btu per hour (4.8
m3per 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 unconfined space.
Where the air infiltration rate of a structure is known, the Known Air
Infiltration 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 confined or unconfined.
DETERMINING FRESH-AIR FLOW FOR FIREBOX LOCATION
Determining if You Have a Confined or Unconfined Space Using
the Standard Method
Use this work sheet to determine if you have a confined or uncon-
fined space.
Space: Includes the room in which you will install heater plus any
adjoining 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) = 3168 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: 3168 cu. ft. (volume of space) x 20 = 63,360 (maximum
Btu/Hr the space can support)
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free heater ______Btu/Hr
Gas water heater* ______Btu/Hr
Gas furnace ______Btu/Hr
Vented gas heater ______Btu/Hr
Gas fireplace logs ______Btu/Hr
Other gas appliances* + ____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 heater + 39,000 Btu/Hr
Total = 79,000 Btu/Hr
WARNING: 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 National Fuel Gas Code, ANSI Z223.1/NFPA 54,
the International Fuel Gas Code, or applicable local
codes. Read thefollowing instructions toensure proper
fresh air for this and other fuel-burning appliances in
your home.
Today’s homes are built more energy efficient than ever. New materi-
als, 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 efficient, 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 fireplaces, 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
classifications:
1. Unusually Tight Construction
2. Unconfined Space
3. Confined Space
The information on Pages 5 through 7 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 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 (6 x
10-11 kg per pa-sec-m2) 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 floors, 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
additional fresh air. See Ventilation Air From Outdoors, Page 7.
If your home does not meet all of the three criteria above, proceed
to Determining Fresh-Air Flow for Firebox Location.
AIR FOR COMBUSTION AND VENTILATION
