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126712-01C
9
DETERMINING FRESH-AIR FLOW
FOR HEATER LOCATION
Determining if You Have a Confi ned or
Unconfi ned Space Using the Standard
Method
Use this work sheet to determine if you have
a confi ned or unconfi ned 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 22 ft. (length) x 18 ft.
(width) x 8 ft. (ceiling height) = 3,168 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 = (Maxi-
mum Btu/Hr the space can support)
Example:
3,168 cu. ft. (volume of space) x 20
= 63,360 (maximum Btu/Hr space can support)
3. Add the Btu/Hr of all fuel burning appliances
in the space.
Vent-free
fi replace
_________ Btu/Hr
Gas water heater*
_________ Btu/Hr
Gas
furnace
_________ Btu/Hr
Vented gas heater
_________ Btu/Hr
Gas
fi 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
fi replace
+ _________ Btu/Hr
Total
=
_________ Btu/Hr
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 example is a confi ned 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
unconfi ned space, remove door to adjoining
room or add ventilation grills between rooms.
See
Ventilation Air From Inside Building
.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors,
Page 10
.
C. Install a lower Btu/Hr fi replace, if lower Btu/
Hr size makes room unconfi ned.
If the actual Btu/Hr used is less than the
maximum Btu/Hr the space can support, the
space is an unconfi ned space. You will need
no additional fresh air ventilation.
40,000
39,000
79,000
WARNING: If the area in
which the heater may be oper-
ated does not meet the required
volume for indoor combustion
air, combustion and ventilation
air shall be provided by one of
the methods described in the
National Fuel Gas Code, ANSI
Z223.1/NFPA 54, the Internation-
al Fuel Gas Code, or applicable
local codes.
