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200020-01A
8
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if You Have a Confined or Unconfined Space
3. Add the Btu/Hr of all fuel burning appli-
ances 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 appli-
ances. 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)
56,000 Btu/Hr (actual amount
of Btu/Hr used)
AIR FOR COMBUSTION AND VENTILATION
30,000
26,000
56,000
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
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 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
3
) (volume
of space) x 20 = 51,200 (maximum Btu/
Hr the space can support)
Unusually Tight Construction
The air that leaks around doors and windows
may provide enough fresh air for combustion
and ventilation. However, in buildings of un-
usually tight construction, you must provide
additional fresh air.
Unusually tight construction is defined as
construction where:
a. walls and ceilings exposed to the outside
atmosphere have a continuous water
vapor retarder with a rating of one perm
(6 x 10
-11
kg per pa-sec-m
2
) or less with
openings gasketed or sealed and
b. weather stripping has been added on
openable windows and doors and
c. caulking or sealants are applied to areas
such as joints around window and door
frames, between sole plates and floors,
between wall-ceiling joints, between wall
panels, at penetrations for plumbing, elec-
trical and gas lines and at other openings.
If your home meets all of these three criteria,
you must provide additional fresh air. See
Ventilation Air From Outdoors
, page 9.
If your home does not meet all of the three
criteria above, proceed to
Determining Fresh-
Air Flow For Heater Location
.
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/hr (4.8 m
3
per kw) of the aggregate
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 unconfined space.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grills between them.
