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AIR FOR
COMBUSTION
AND
VENTILATION
Continued
DETERMINING AIR FLOW FOR HEATER LOCATION
Determining if You Have a Confined or Unconfined Space
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. (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
+
31,500
Btu/Hr
Total
=
71,500
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)
71,500
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 7.
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.
