www.fmiproducts.com
121082-01K
8
AIR FOR COMBUSTION AND VENTILATION
Continued
DETERMINING FRESH-AIR FLOW
FOR HEATER LOCATION
Determining if You Have a Confined or
Unconfined Space
Use this work sheet to determine if you have
a confined or unconfined 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.
Vent-free fireplace
__________ 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 fireplace
+
________ 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 sup-
port. 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
unconfined space, remove door to adjoining
room or add ventilation grills between rooms.
See
Ventilation Air From Inside Building,
page 9
.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors,
page 9.
C. Install a lower Btu/Hr fireplace, 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 unconfined 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.
40,000
39,000
79,000
