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AIR FOR COMBUSTION AND VENTILATION
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. (6.1 m)
(length) x 16 ft. (4.88 m) (width) x
8 ft. (2.44 m) (ceiling height) = 2560 cu.
ft. (72.49 m
) (volume of space)
3
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 deter-
mine the maximum Btu/Hr the space can
support.
________(volume of space) x 20 =
(Maximum Btu/Hr the space can support)
Example: 2560 cu. ft. (72.49 m
of space) x 20 = 51,200 (maximum Btu/
Hr the space can support)
3. Add the Btu/Hr of all fuel burning appli-
ances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas fireplace logs
Other gas appliances*+ _______ Btu/Hr
Total
* Do not include direct-vent gas appli-
ances. Direct-vent draws combustion
air from the outdoors and vents to the
outdoors.
8
) (volume
3
_________ Btu/Hr
_________ Btu/Hr
_________ Btu/Hr
_________ Btu/Hr
_________ Btu/Hr
= ________ Btu/Hr
www.sureheat.com
Example:
Gas water heater
Vent-free heater
Total
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)
56,000 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 heater, if lower Btu/
Hr size makes room unconfined. If the ac-
tual 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 is
smaller than that defined as
an unconfined 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, the In-
ternational Fuel Gas Code, or
applicable local codes.
__________ Btu/Hr
30,000
+ _________ Btu/Hr
26,000
= _________ Btu/Hr
56,000
200040-01A
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