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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. (6.1 m) (length) x
16 ft. (4.88 m) (width) x 8 ft. (2.44 m) (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 = (Maxi-
mum Btu/Hr the space can support)
Example: 2560 cu. ft. (72.4 m
3
) (volume of space) x 20
= 51,200 (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 replace logs _____________ Btu/Hr
Other gas appliances* + ____________ Btu/Hr
Total = ____________ Btu/Hr
* Do not include direct-vent gas appliances. Di-
rect-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: 51,200 Btu/Hr (maximum the space
can support)
60,000 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 maxi-
mum 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 adjoin-
ing 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.
B. Vent room directly to the outdoors. See Ventila-
tion Air From Outdoors, page 7.
AIR FOR COMBUSTION
AND VENTILATION
Continued
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 maximum
Btu/Hr the space can support, the space is an un-
conned 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.
VENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoining un-
conned space. When ventilating to an adjoining
unconned space, you must provide two perma-
nent openings: one within 12" (30.4 cm) of the
ceiling and one within 12" (30.4 cm) of the oor
on the wall connecting the two spaces (see options
1 and 2, Figure 2). You can also remove door into
adjoining room (see option 3, Figure 2). 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.
40,000
20,000
60,000
Figure 2 - Ventilation Air from Inside
Building
Or
Remove
Door into
Adjoining
Room,
Option 3
Ventilation Grills
Into Adjoining Room,
Option 2
12"
12"
Ventilation
Grills
into Adjoining
Room,
Option 1