104463-01E
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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 vol-
ume 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 (maxi-
mum 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
combustion air from the outdoors and vents to the outdoors.
Example:
Gas water heater
40,000
Btu/Hr
Vent-free heater
+
30,000
Btu/Hr
Total
=
70,000
Btu/Hr
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.
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)
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
Outdoors, page 6.
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.
AIR FOR COMBUSTION AND VENTILATION
Determining Fresh-Air Flow for Heater Location
