www.fmiproducts.com
113093-01J
7
AIR FOR COMBUSTION AND VENTILATION
Continued
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/
NFPA 54
defines a confined space as a space
whose volume is less than 50 cubic feet per
1,000 Btu per hour (4.8 m
3
per kw) of the ag-
gregate input rating of all appliances installed
in that space and an unconfined space as a
space whose volume is not less than 50 cubic
feet per 1,000 Btu per hour (4.8 m
3
per kw)
of the aggregate input rating of all appliances
installed in that space. Rooms communicating
directly with the space in which the appliances
are installed*, through openings not furnished
with doors, are considered a part of the un-
confined space.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grills between them.
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 20 ft. (length) x 16 ft.
(width) x 8 ft. (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. (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
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
fir
________ 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)
73,000 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 adjoin-
ing room or add ventilation grills between
rooms. See
Ventilation Air From Inside
Building
, page 8
.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors,
page 8.
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 maxi-
mum 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
33,000
73,000