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118621-01B6
DETERMINING FRESH-AIR FLOW
FOR HEATER LOCATION
Determining if You Have a Conned or
Unconned Space
Use this work sheet to determine if you have a
conned or unconned 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 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 sup-
port)
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 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 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 can support)
_______ Btu/Hr (actual amount used)
Example:
51,200 Btu/Hr (maximum can support)
60,000 Btu/Hr (actual amount used)
The space in the above example is a conned
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 unconned space, remove door to adjoin-
ing room or add ventilation grills between
rooms. See Ventilation Air From Inside
Building, page 7.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 7.
C. Install a lower Btu/Hr heater, if lower Btu/Hr
size makes room unconned.
If the actual Btu/Hr used is less than the maxi-
mum Btu/Hr the space can support, the space is
an unconned 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 dened
as an unconned 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
20,000
60,000