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DETERMINING FRESH-AIR FLOW FOR
HEATER LOCATION
DETERMINE IF YOU HAVE UNUSUALLY TIGHT CONSTRICTION OR UNCONFINED SPACE
Use this worksheet to determine if you have confined or unconfined space.
SPACE: Includes the room in which you will install heater plus adjoining rooms with
doorless passageways or ventilation grills between rooms.
1. Determine the volume of 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 volume
of these rooms to total volume of the space.
2. Divide the space volume by 50 cubic feet to determine the maximum BTU/Hr 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 space can support)
3. Add the BTU/Hr of all fuel burning appliances in 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 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 unusually tight construction space because 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:
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