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1. Determine the volume of the space (length x width x height).
Length x Width x Height =_________cu.ft.(volume of space)
EXAMPLE: 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
51200 (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 40000 BTU/Hr
Vent-free heater + 18000 B
TU/Hr
Total = 58000 BTU/Hr
*Does 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: 51200 BTU/Hr (maximum the space can support)
58000 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 37.
B. Vent room directly to the outdoors. See “Ventilation Air From Outdoors”, page 38.
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.
WAR N I N G : YOU MUST PROVIDE ADDITIONAL VENTILATION AIR IN A
CONFINED SPACE
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