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121255-01A
6
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 pas
-
sageways 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
3
) (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. (72.49 m
3
) (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 heater
__________
Btu/Hr
Gas water heater*
__________
Btu/Hr
Gas furnace
__________
Btu/Hr
Vented gas heater
__________
Btu/Hr
Gas fireplace logs
__________
Btu/Hr
Other gas appl __________
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 heater
+
_________
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)
60,000 Btu/Hr (actual amount of
Btu/Hr used)
AIR FOR COMbUSTION
AND VENTILATION
Continued
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.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors,
page 7.
C. Install a lower Btu/Hr heater, 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 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 Section 5.3
or applicable local codes.
vENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoin
-
ing unconfined space. When ventilating to
an adjoining unconfined space, you must
provide two permanent openings: one within
12" (30.5 cm) of the ceiling and one within
12" (30.5 cm) of the floor on the wall con
-
necting the two spaces (see options 1 and 2,
Figure 2, page 7). You can also remove door
into adjoining room (see option 3, Figure 2,
page 7). Follow the
National Fuel Gas Code,
ANSI Z223.1/NFPA 54, Section 5.3, Air for
Combustion and Ventilation
for required size
of ventilation grills or ducts.
40,000
20,000
60,000
