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6
AIR FoR CoMBUsTIoN
ANd VeNTIlATIoN
Continued
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 con
-
fined or unconfined space.
Space:
Includes the room in which you will install
heater plus any adjoining rooms with doorless pas
-
sageways 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
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:
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. Di
-
rect-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
40,000
20,000
60,000
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)
60,000 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 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 adjoin
-
ing 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
Ventila-
tion 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 uncon
-
fined space. You will need no additional fresh air
ventilation.
WARNING: If the area in
which the heater may be oper
-
ated 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.
