www.desatech.com
107882-01M
6
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 pas-
sageways 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. (6.1 m) (length) x 16
ft. (4.88 m) (width) x 8 ft. (2.44 m) (ceiling height)
= 2560 cu. ft. (72.49 m
3
) (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. (72.49 m
3
) (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. Di-
rect-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
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)
60,000 Btu/Hr (actual amount of
Btu/Hr used)
AIR FOR COMBUSTION
AND VENTILATION
Continued
The space in the above example is a confined space
because the actual Btu/Hr used is more than the maxi-
mum 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 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.
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 un-
confined space. You will need no additional fresh
air ventilation.
WARNING: If the area in
which the heater may be oper-
ated 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 permanent
openings: one within 12" (30.4 cm) of the ceiling
and one within 12" (30.4 cm) of the floor on the
wall connecting the two spaces (see options 1 and
2, Figure 2, page 7). You can also remove door
into adjoining room (see option 3, Figure 2, page
7). 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
20,000
60,000
