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*Adjoining rooms are communication only if there
are odorless passageways or ventilation grills be-
tween them.
DETERMINING THE TYPE OF HEATER
LOCATION SPACE:
Use this method to determine if you have a confined or
unconfined space.
Note: the space includes the room in which you
install heater plus any adjoining rooms with doorless
passageways or ventilation grills between the rooms.
1. Find the volume of the space by multiplying room
length x width x height.
Example: Space size 18ft (length) x 18ft. (width) x 8ft.
(height) = 2592
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. Divide the space volume by 50 cubic feet to deter-
mine the maximum Btu/hr the space can support.
Example: 2592 cu.ft. (volume of space) / 50 cu.ft. =
51.8 or 51,800 (maximum Btu/hr the space
can support)
WARNING: If the area in which the heater may be
operated is smaller than defined as an unconfined
space or if the building is of unusually tight con-
struction, provide adequate combustion and ventila-
tion air by the methods described in the National
Fuel Gas Code, NFPA 54/ ANSI Z223.1, Section
5.3 or applicable local codes.
3. Add the Btu/hr of all the fuel-burning appliances
in the space such as, Vent–free heater, Gas water
heater, Gas furnace, Vented gas heater, Gas fire-
place logs, and Other gas appliances*
*Do not include direct-vent gas appliances. Direct-
vent draws combustion air from the outdoors and
vents to the outdoors.
Example:
Gas water heater
Vent Free Heater +
Total
4. Compare the maximum Btu/hr the space can support
with the actual amount of Btu/hr used.
Example:
51,800 Btu/hr (maximum Btu/hr 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 support.
You must provide additional fresh air. Your options
are as follows:
A. Rework worksheet, and the space of an adjoining
room. If the extra space provides an unconfined
space, remove door to adjoining room or add venti-
lation grills between the rooms. See Ventilation Air
40,000 Btu/hr
20,000 Btu/hr
=60,000 Btu/hr
Unvented Natural Gas Vent Free Heaters
From Inside Building (Figure 2).
B. Vent room directly to the outdoors. See Ventilation
Air From Outdoors (Figure 3).
C. Install a lower Btu/hr heater if lower Btu/hr size
makes room unconfined.
If actual Btu/hr used is less than the maximum Btu/
hr the space can support, the space is an uncon-
fined space. You will need no additional fresh air
ventilation.
VENTILATION AIR
Ventilation from Inside Building
This fresh air would come from an adjoining unconfined
space. When ventilation 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
& 2 of fig. 2). You can also remove door into adjoin-
ing room (see option3, fig 2). Follow the National Fuel
Gas Code NFPA 54/ ANSI Z223.1, Section 5.3, Air for
Combustion and Ventilation for required size of ventila-
tion grills or ducts.
Or remove
Ventilation
door into
Gills into
Adjoining
Adjoining
Room -
Room -
Option 3
Option 1
OUTLET AIR
OUTLET
AIR
INLET
AIR
5
Installation Instructions and Owner's Manual
12"
Ventilation Gills into
Adjoining Room - Option 2
12"
Figure 2.
VENTILATION AIR
VENTILATED
ATTIC
TO ATTIC
TO CRAWL
SPACE
VENTILATION CRAWL SPACE
Figure 3.
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