Desa CTR25NR - Manual (Page 6)

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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 (kw) 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 (kw) of all fuel burning appli-
ances in the space.
Vent-free heater ________ Btu/Hr (kw)
Gas water heater* ________ Btu/Hr (kw)
Gas furnace ________ Btu/Hr (kw)
Vented gas heater ________ Btu/Hr (kw)
Gas fireplace logs ________ Btu/Hr (kw)
Other gas appliances* + ________ Btu/Hr (kw)
Total = ________ Btu/Hr (kw)
* Do not include direct-vent gas appliances. Di-
rect-vent draws combustion air from the outdoors
and vents to the outdoors.
Example:
Gas water heater ___________ Btu/Hr (kw)
Vent-free heater ___________ Btu/Hr (kw)
Total ___________ Btu/Hr (kw)
4. Compare the maximum Btu/Hr (kw) the space can
support with the actual amount of Btu/Hr (kw) used.
___________Btu/Hr (kw) (maximum the space can support)
___________Btu/Hr (kw) (actual amount of Btu/Hr used)
Example: 51,200 Btu/Hr (15 kw) (maximum
the space can support)
62,000 Btu/Hr (18.2 kw) (actual
amount of Btu/Hr used)
The space in the above example is a confined space
because the actual Btu/Hr (kw) used is more than the
maximum Btu/Hr (kw) the space can support. You must
provide additional fresh air. Your options are as follows:
A. Rework worksheet, adding the space of an adjoin-
ing 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 Ventila-
tion Air From Outdoors, page 7.
AIR FOR COMBUSTION
AND VENTILATION
Continued
C. Install a lower Btu/Hr (kw) heater, if lower Btu/Hr
(kw) size makes room unconfined.
If the actual Btu/Hr (kw) used is less than the maxi-
mum Btu/Hr (kw) 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 is
smaller than that defined as
an unconfined space or if the
building is of unusually tight
construction, provide adequate
combustion and ventilation air
by one of the methods described
in the National Fuel Gas Code,
ANSI Z223.1/NFPA 54 Section 5.3
or applicable local codes.
VENTILATION AIR
Ventilation Air From Inside Building
This fresh air would come from an adjoining un-
confined space. When ventilating to an adjoining
unconfined space, you must provide two perma-
nent openings: one within 12" (30.5 cm) of the
ceiling and one within 12" (30.5 cm) of the floor
on the wall connecting the two spaces (see options
1 and 2, Figure 2). You can also remove door into
adjoining room (see option 3, Figure 2). Follow the
National Fuel Gas Code, ANSI Z223.1/NFPA 54,
Section 5.3, Air for Combustion and Ventilation for
required size of ventilation grills or ducts.
40,000 (11.7)
+ 22,000 (6.4)
= 62,000 (18.2)
Figure 2 - Ventilation Air from Inside
Building
Or
Remove
Door into
Adjoining
Room,
Option 3
Ventilation Grills
Into Adjoining Room,
Option 2
12"
12"
Ventilation
Grills
into Adjoining
Room,
Option 1
12" (30,48 cm)
12" (30,48 cm)