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AIR FOR COMBUSTION
AND VENTILATION
Continued
Confined and Unconfined Space
The National Fuel Gas Code ANSI Z223.1/NFPA
54 defines a confined space as a space whose
volume is less than 50 cubic feet per 1,000 Btu
per hour (4.8 m
per kw) of the aggregate input
3
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 m
per kw) of the aggregate input rating of
3
all appliances installed in that space. Rooms com-
municating directly with the space in which the
appliances are installed*, through openings not
furnished with doors, are considered a part of the
unconfined space.
* 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 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 door-
less 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)
6
3. Add the Btu/Hr of all fuel burning appliances
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 appliances.
Direct-vent draws combustion air from the
outdoors and vents to the outdoors.
Example:
Gas water heater
Vent-free heater
Total
4. Compare the maximum Btu/Hr the space can
support with the actual amount of Btu/Hr used.
_____________Btu/Hr (maximum the space
___________ Btu/Hr (actual amount of
Example:
The space in the above example is a confined space
because the actual Btu/Hr used is more than the maxi-
mum 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 7.
B. Vent room directly to the outdoors. See Ven-
tilation Air From Outdoors, page 7.
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.
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_________ Btu/Hr
_________ Btu/Hr
________ Btu/Hr
________ Btu/Hr
________ Btu/Hr
= ________ Btu/Hr
40,000
________ Btu/Hr
30,000
+ ________ Btu/Hr
70,000
= ________ Btu/Hr
can support)
Btu/Hr used)
51,200 Btu/Hr (maximum the
space can support)
70,000 Btu/Hr (actual amount
of Btu/Hr used)
115580-01B
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