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AIR FOR COMBUSTION AND VENTILATION
DETERMINING FRESH-AIR FLOW
FOR HEATER LOCATION
Determining if You Have a Confined or
Unconfined Space
Use this work sheet to determine if you have
a confined or unconfined space.
: Includes the room in which you will
Space
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 deter-
mine the maximum Btu/Hr the space can
support.
_____ (volume of space) x 20 = (Maxi-
mum 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 appli-
ances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas fireplace logs
Other gas appliances* + _______ Btu/Hr
TotaL
* Do not include direct-vent gas appli-
ances. Direct-vent draws combustion
air from the outdoors and vents to the
outdoors.
Example:
Gas water heater
Vent-free heater
Total
8
Continued
_______ Btu/Hr
_______ Btu/Hr
_______ Btu/Hr
_______ Btu/Hr
_______ Btu/Hr
= _______ Btu/Hr
40,000
_________ Btu/Hr
39,000
+ ________ Btu/Hr
79,000
= ________ Btu/Hr
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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)
The space in the above example is a confined
space because the actual Btu/Hr used is more
than the maximum Btu/Hr the space can sup-
port. 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 9.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 9.
C. Install a lower Btu/Hr heater, if lower
Btu/Hr size makes room unconfined.
If the actual Btu/Hr used is less than the
maximum Btu/Hr the space can support, the
space is an unconfined space. You will need
no additional fresh air ventilation.
WARNING: If the area in which
the heater may be operated does
not meet the required volume for
indoor combustion air, combus-
tion and ventilation 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 applicable local codes.
127032-01A
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