Desa GA3700 - Manual (Page 7)

www.desatech.com 113109-01G 7
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 = (Maxi-
mum 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 fireplace __________ 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 fireplace + _________ 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)
73,000 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 adjoining
room or add ventilation grills between rooms.
See Ventilation Air From Inside Building.
40,000
33,000
73,000
AIR FOR COMbUSTION AND VENTILATION
Continued
Figure 3 - Ventilation Air from Inside
Building
Or
Remove
Door into
Adjoining
Room,
Option
3
Ventilation Grills
Into Adjoining Room,
Option 2
Ventilation
Grills
Into Adjoining
Room,
Option 1
12"
12"
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 8.
C. Install a lower Btu/Hr fireplace, 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 oper-
ated does not meet the required
volume for indoor combustion
air, combustion and ventilation
air shall be provided by one of
the methods described in the
National Fuel Gas Code, ANSI
Z223.1/NFPA 54, the Internation-
al Fuel Gas Code, or applicable
local codes.
vENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoining
unconfined space. When ventilating to an
adjoining unconfined space, you must provide
two permanent openings: one within 12" of the
ceiling and one within 12" of the floor on the
wall connecting the two spaces (see options
1 and 2, Figure 3). You can also remove door
into adjoining room (see option 3, Figure 3).
Follow the National Fuel Gas Code, ANSI
Z223.1/NFPA 54, Air for Combustion and
Ventilation for required size of ventilation
grills or ducts.