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105163-01E 7
DETERMINING FRESH-AIR FLOW
FOR FIREBOX 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 22 ft. (length) x 18 ft.
(width) x 8 ft. (ceiling height) = 3168 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 sup-
port.
________ (volume of space) x 20 = (Maxi-
mum Btu/Hr the space can support)
Example: 3168 cu. ft. (volume of space) x 20
= 63,360 (maximum Btu/Hr the space can
support)
3. Add the Btu/Hr of all fuel burning appliances
in the space.
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
Gas rebox logs + _________Btu/Hr
Total = _________Btu/Hr
AIR FOR COMBUSTION AND VENTILATION
Continued
40,000
39,000
79,000
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: 63,360 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 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 work sheet, adding the space
of an adjoining room. If the extra space
provides an unconned 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
Ventilation Air from Outdoors, page 8.
C. Install a lower Btu/Hr gas log heater, if
lower Btu/Hr size makes room uncon-
ned.
If the actual Btu/Hr used is less than the
maximum 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 operated does
not meet the required volume for
indoor combustion air, combus-
tion and ventilation air shall be
provided by one of the methods
described in the National Fuel
Gas Code, ANSI Z223.1/NFPA 54,
the International Fuel Gas Code,
or applicable local codes.