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GAS RESIDENTIAL HEATERS
AIR FOR
COMBUSTION AND
VENTILATION
Continued
DETERMINING 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)
2304 cu. ft. (volume of space)
Example:
3. Add the Btu/Hr of all fuel burning appliances in the space.
Vent-free heater
Gas water heater*
Gas furnace
Vented gas heater
Gas fireplace logs
Other gas appliances*
Total
Gas water heater
Example:
Vent-free heater
Total
* 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)
46,100
Btu/Hr (maximum the space can support)
Example:
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 adjoining
room or add ventilation grills between rooms. See Ventilation Air From Inside Building, page 5.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 5.
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.
50 cu. ft. = (Maximum Btu/Hr the space can support)
50 cu. ft. = 46.1 or 46,100 (maximum Btu/Hr the space can support)
___________________ Btu/Hr
___________________ Btu/Hr
___________________ Btu/Hr
___________________ Btu/Hr
___________________ Btu/Hr
+ ___________________ Btu/Hr
= ___________________ Btu/Hr
40,000
+
10,000
=
50,000
Btu/Hr
Btu/Hr
Btu/Hr
4
103549
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