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126810-01B
7
AIR FOR COMBUSTION AND VENTILATION
Continued
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/hr (4.8 m
3
per kw) of the ag-
gregate 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/hr (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 uncon-
fi ned.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grills between them.
DETERMINING FRESH-AIR FLOW FOR
HEATER 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 unconfi ned space.
Space:
Includes the room in which you will install
fi replace 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 20 ft. (length) x 16 ft.
(width) x 8 ft. (ceiling height) = 2560 cu. ft.
(volume of space)
If additional ventilation to adjoining room is sup-
plied 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:
2560 cu. ft. (volume of space) x 20 =
51,200 (maximum Btu/Hr the space can sup-
port)
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 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
__________ Btu/Hr
Vent-free
fi replace
+ _________ Btu/Hr
Total
=
_________ Btu/Hr
4. Compare the maximum Btu/Hr the space can sup-
port with the actual amount of Btu/Hr used.
_______ Btu/Hr (maximum can support)
_______ Btu/Hr (actual amount used)
Example:
51,200 Btu/Hr (maximum the space
can support)
73,000 Btu/Hr (actual amount of Btu/
Hr used)
The space in the above example is a confi ned
space because the actual Btu/Hr used is more
than the maximum Btu/Hr the space can support.
You must provide additional fresh air. Your options
are as follows:
A. Rework worksheet, adding the space of an
adjoining room. If the extra space provides an
unconfined space, remove door to adjoining
room or add ventilation grills between rooms. See
Ventilation Air From Inside Building, Page 8.
B. Vent room directly to the outdoors. See
Ventila-
tion Air From Outdoors, Page 8
.
C. Install a lower Btu/Hr fi replace, if lower Btu/Hr
size makes room unconfi ned.
If the actual Btu/Hr used is less than the maximum
Btu/Hr the space can support,
the space is an un-
confi ned space. You will need no additional fresh
air ventilation.
40,000
33,000
73,000
WARNING: If the area in which the
appliance may be operated does not
meet the required volume for indoor
combustion air, combustion and ven-
tilation air shall be provided by one of
the methods described in the National
Fuel Gas Code, ANSI Z223.1/NFPA 54,
the International Fuel Gas Code, or ap-
plicable local codes.
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