Desa VCM-50U - Manual (Page 9)

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AIr For CoMBUsTIoN ANd VeNTIlATIoN
Continued
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 22 ft. (length) x 18 ft.
(width) x 8 ft. (ceiling height) = 3,168 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: 3,168 cu. ft. (volume of space) x 20 =
63,360 (maximum Btu/Hr 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: 63,360 Btu/Hr (maximum the
space can support)
79,000 Btu/Hr (actual amount of
Btu/Hr used)
The space in the 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.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors, page 10.
C. Install a lower Btu/Hr fireplace, if lower Btu/
Hr size makes room unconfined.
Figure 4 - 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"
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.
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 4). You can also remove door
into adjoining room (see option 3, Figure 4 ).
Follow the National Fuel Gas Code, ANSI
Z223.1/NFPA 54, Air for Combustion and
Ventilation for required size of ventilation
grills or ducts.
40,000
39,000
79,000