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104464-01E
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For more information, visit www.desatech.com
5
5
AIR FOR COMBUSTION AND
VENTILATION
Continued
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 uncon-
fined 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. 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)
70,000 Btu/Hr (actual amount of Btu/Hr used)
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.
40,000
30,000
70,000
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 6.
B. Vent room directly to the outdoors. See Ventilation Air From Out-
doors, page 6.
C. Install a lower Btu/Hr heater, if lower Btu/Hr size makes room un-
confined.
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.
AIR FOR COMBUSTION AND VENTILATION
Determining Fresh-Air Flow for Heater Location