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103873
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 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:
2560 cu. ft. (volume of space) ÷ 50 cu. ft. = 51.2 or 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 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 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:
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 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 7.
B. Vent room directly to the outdoors. See Ventilation Air From Outdoors, page 8.
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.