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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.
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 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 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
________ Btu/Hr
Vent-free heater + ________ Btu/Hr
Total = ________ Btu/Hr
AIR FOR COMBUSTION
AND VENTILATION
Continued
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:
51,200 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 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
Ven-
tilation Air From Outdoors
, page 8.
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 maxi-
mum 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 firebox and gas log
heater may be operated is
smaller than that defined as
an unconfined space or if the
building is of 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 Section 5.3
or applicable local codes.
40,000
39,000
79,000
