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122274-01G 9
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) = 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 replace _________ 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.
Direct-vent draws combustion air from the
outdoors and vents to the outdoors.
Example:
Gas water heater _________Btu/Hr
Vent-free 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 conned space
because the actual Btu/Hr used is more than the
maximum Btu/Hr the space can su pport. 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
uncon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 replace, if lower Btu/
Hr size makes room unconned.

Figure 4 - Ventilation Air from Inside

Building

Or
Remove
Door into
Adjoining
Room,
Option
3
Ventilation Grills
Into Adjoining Room,
Option 2
Ventilation
Grills Into
Adjoining
Room,
Option 1
12"
12"

If the actual Btu/Hr used is less than the

maximum Btu/Hr the space can support, the

space is an unconned 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.

vENTILATION AIR

Ventilation Air From Inside Building

This fresh air would come from an adjoining

unconned space. When ventilating to an

adjoining unconned space, you must provide

two permanent openings: one within 12" of the

ceiling and one within 12" of the oor 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 4 ).

Follow the National Fuel Gas Code, ANSI

Z223.1/NFPA 54, Air for Combustion and

Ventilation for required size of ventilation

grills or ducts.

40,000
39,000
79,000