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104190
OWNER’S MANUAL
FRESH AIR FOR
COMBUSTION AND
VENTILATION
Continued
DETERMINING FRESH-AIR
FLOW FOR HEATER
LOCATION
Determining if You Have a
Confined or Unconfined Space
Use this worksheet 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 open-
ings, add the volume of these rooms to
the total volume of the space.
2. Divide the space volume by 50 cubic
feet to determine the maximum Btu/Hr
the space can support.
_______________ (volume of space)
÷ 50 cu. ft. = (Maximum Btu/Hr the
space can support)
Example:
2560 cu. ft. (volume of
space) ÷ 50 cu. ft. = 51.2 or 51,200
(maximum Btu/Hr the space can sup-
port)
3. Add the Btu/Hr of all fuel burning ap-
pliances 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 appliances* + ___ Btu/Hr
Total = ___ Btu/Hr
Example:
Gas water heater 40,000 Btu/Hr
Vent-free heater + 20,000 Btu/Hr
Total = 60,000 Btu/Hr
* Do not include direct-vent gas appli-
ances. Direct-vent draws combustion
air from the outdoors and vents to the
outdoors.
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)60,000 Btu/Hr
(actual amount of Btu/Hr used)
The space in the above example is a con-
fined space because the actual Btu/Hr used
is more than the maximum Btu/Hr the space
can support. 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 ventila-
tion grills between rooms. See Ventila-
tion Air From Inside Building, page 6.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 6.
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
maximum Btu/Hr the space can support, the
space is an unconfined space. You will need
no additional fresh air ventilation.
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