Desa WMN20A - Manual (Page 6)

www.desatech.com 124002-01C 6
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 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 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 combustion air from the
outdoors and vents to the outdoors.
Example:
Gas water heater ____________ Btu/Hr
Vent-free heater + ___________ Btu/Hr
Total = ___________ Btu/Hr
40,000
20,000
60,000
4. Compare the maximum Btu/Hr the space
can support with the actual amount of Btu/
Hr used.
_______ Btu/Hr (maximum can support)
_______ Btu/Hr (actual amount used)
Example:
51,200 Btu/Hr (maximum the space can
support)
60,000 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 sup-
port. 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 adjoin-
ing 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 Outdoors, 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.
WARNING: If the area in which
the heater may be operated does
not meet the required volume for
indoor combustion air, combus-
tion and ventilation air shall be
provided by one of the methods
described in the National Fuel
Gas Code, ANSI Z223.1/NFPA 54,
the International Fuel Gas Code,
or applicable local codes.