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OWNER’S MANUAL
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 18 ft. (length) x 16 ft. (width) x 8 ft. (ceiling height) = 2304 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. 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:
2304 cu. ft. (volume of space) ÷ 50 cu. ft. = 46.1 or 46,100 (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 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.
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:
46,100 Btu/Hr (maximum the space can support)
50,000 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 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 adjoin-
ing room or add ventilation grills between rooms. See Ventilation 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.
AIR FOR
COMBUSTION AND
VENTILATION
Continued
Example:
Gas water heater
40,000
Btu/Hr
Vent-free heater +
10,000
Btu/Hr
Total =
50,000
Btu/Hr
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, ANS Z223.1, Section 5.3
or applicable local codes.
Continued