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8
AIR FOR COMBUSTION AND VENTILATION CONTINUED
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 the firebox 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 22 ft. (length) x 18 ft. (width) x 8 ft. (ceiling height) =
3168 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: 3168 cu. Ft. (volume of space) 50 cu. Ft. = 63.3 or 63,300 (maximum
BTU/Hr the space can support)
3. Add the BTU/Hr of all fuel-burning appliances in the space.
Vent-free Firebox __________________ BTU/Hr
Gas water heater* __________________ BTU/Hr
Gas furnace __________________ BTU/Hr
Vented gas heater __________________ BTU/Hr
Gas firebox logs __________________ BTU/Hr
Other gas appliances* + __________________ BTU/Hr
Total = __________________ BTU/Hr
Example: Gas water Heater 40,000 BTU/Hr
Vent-free firebox with log heater + 39,000 BTU/Hr
Total = 79,000 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: 63,300 BTU/Hr (maximum the space can support)
79,000 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 9.