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115254-01A
8
AIR FOR COMBUSTION
AND VENTILATION
Continued
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 support.
_______(volume of space) x 20 = (Maximum
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.
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.
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
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 confined
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:
VENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoining un
-
confined space. When ventilating to an adjoining
unconfined space, you must provide two perma
-
nent openings: one within 12" of the ceiling and
one within 12" of the floor on the wall connecting
the two spaces (see options 1 and 2, Figure 4). You
can also remove door into adjoining room (see
option 3, Figure 3). 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 or ducts.
Figure 3 - Ventilation Air from Inside
Building
40,000
39,000
79,000
Or
Remove
Door into
Adjoining
Room,
Option
3
Ventilation Grills
Into Adjoining Room,
Option
2
Ve
ntilation
Grills
Into
Adjoining
Room,
Option 1
12"
12"
A. Rework worksheet, adding the space of an
adjoining 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
.
B. Vent room directly to the outdoors. See Ven
-
tilation Air From Outdoors, page 9.
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 un
-
confined space. You will need no additional fresh
air ventilation.
WARNING: If the area in which
the heater may be operated 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.