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6
DETERMINING FRESH-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 open-
ings, add the volume of these rooms to the total volume of the space.
2.
Multiply the space volume by 20 to determine the maximum Btu/Hr
the space can support.
__________ (volume of space) x 20 = (Maximum Btu/Hr the space
can support)
Example:
2560 cu. ft. (volume of space) x 20 = 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
* Do not include direct-vent gas appliances. Direct-vent draws com-
bustion air from the outdoors and vents to the outdoors.
Example:
Gas water heater
_____________ Btu/Hr
Vent-free heater
+ _____________ Btu/Hr
Total
= _____________ Btu/Hr
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)
79,000 Btu/Hr (actual amount of Btu/Hr used)
AIR FOR COMBUSTION AND
VENTILATION
Continued
WARNING: If the area in which the heater may be
operated is smaller than that defined as an uncon-
fined space or if the building is of unusually tight
construction, provide adequate combustion and ven-
tilation air by one of the methods described in the
National Fuel Gas Code, ANSI Z223.1/NFPA 54 Sec-
tion 5.3 or applicable local codes.
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 ex-
tra 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 Out-
doors
, 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.
40,000
39,000
79,000
AIR FOR COMBUSTION AND VENTILATION
Determining Fresh-Air Flow For Heater Location