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126829-01C
7
AIR FOR COMBUSTION AND VENTILATION
Continued
installed is confined or unconfined space. The
standard method defines a confined space as
a space whose volume is less than 50 cubic
feet per 1,000 Btu/hr (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/hr (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.
Where the air infiltration rate of a structure is
known, the Known Air Infiltration Rate Method
may be used. Follow The National Fuel Gas
Code, ANSI Z223.1/NFPA 54 to use this
method to determine if the space is confined
or unconfined.
* 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 Using the Standard
Method
Use this work sheet to determine if you have
a confined or unconfined space.
Space:
Includes the room in which you will install
fireplace plus any adjoining rooms with door
-
less 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 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 can support)
_______ Btu/Hr (actual amount 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.
40,000
33,000
73,000
