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.
If the actual Btu/Hr used is less than the maxi-
mum Btu/Hr the space can support, the space
is an unconfi ned space. You will need no
additional fresh air ventilation.
Confi ned and Unconfi ned Space
AIR FOR COMBUSTION AND VENTILATION
Continued
Example: Space size 16 ft. (length) x 14 ft.
(width) x 8 ft. (ceiling height) = 1792 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: 1792 cu. ft. (volume of space) x
20 = 35,840 (maximum Btu/Hr the 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 space cansupport)
______ Btu/Hr (actual amount used)
Example: 35,840 Btu/Hr (maximum the space
can support)
56,000 Btu/Hr (actual amount of
Btu/Hr used)
The space in the previous 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 adjoin-
ing 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 8.
C. Install a lower Btu/Hr fi replace, if lower Btu/
Hr size makes room unconfi ned.
VENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoining
unconfi ned space. When ventilating to an
adjoining unconfi ned space, you must provide
two permanent openings: one within 12” ( 0.5
cm) of the ceiling and one within 12” (30.5
cm) of the fl oor on the wall connecting the two
spaces (see options 1 and 2, Figure 2, page
7). You can also remove door into adjoining
room (see option 3, Figure 2, page 7). Follow
the National Fuel Gas Code, ANSI Z223.1/
NFPA 54, Section 5.3, Air for Combustion and
Ventilation for required size of ventilation grills
products.
Figure 2 - Ventilation Air from Inside
Building
7
