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Example of Large Room with 1/2 Wall divider.
Figure 1
The following formula can be used to determine the maximum heater
rating per the definition of unconfined space:
Btu/Hr = (L
1
+ L
2
)FT x (W)FT x (H)FT x 1000
50
If the area in which the heater may be operated is smaller than that
defined as an unconfined space, provide adequate combustion and
ventilation air by one of the methods described in the
National Fuel
Gas Code, ANSI Z223.1/NFPA54.
Adhere to all codes, or in their absence, the latest edition of
THE
NATIONAL FUEL GAS CODE ANSI Z223.1/NFPA54
which can be
obtained from:
American National Standards Institute
11 West 42nd St.
New York, NY 10018
OR
National Fire Protection Association, Inc.
Batterymarch Park
Quincy, MA 02269
This heater shall not be installed in a confined space unless provi
-
sions are provided for adequate combustion and ventilation air.
A confined space is an area with volume less than 50 cubic feet per
1,000 Btuh of the combined input rates of all appliances drawing
combustion air from that space. Small areas such as equipment
rooms are confined spaces. Furnaces installed in a confined space
which supply heated air to areas outside the space must draw return
air from outside the space through tightly sealed return air ducts. A
confined space must have 2 openings into the space for combus
-
tion air. One opening must be within 12 inches of the ceiling and
the other must be within 12 inches of the floor. The required sizing
of these openings is determined by whether inside or outside air is
used to support combustion, the method by which the air is brought
to the space (vertical or horizontal duct) and by the total input rate
of all appliances in the space.
Unusually Tight Construction
The air that leaks around doors and windows may provide enough
fresh air for combustion and ventilation. However, in buildings of
unusually tight construction, you must provide additional fresh air.
Unusually tight construction is defined as construction
where:
a. Walls and ceilings exposed to the outside atmosphere have
a continuous water vapor retarder with a rating of one perm
or less with openings gasketed or sealed, and
b. Weather-stripping has been added on openable windows
and doors, and
c. Caulking or sealants are applied to areas such as joints
around window and door frames, between sole plates and
floors, between wall-ceiling joints, between wall panels, at
penetrations for plumbing, electrical, and gas lines, and at
other openings.
If your home meets all of the three criteria above, you must
provide additional fresh air.
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, Air for Combustion and Ventila-
tion, or applicable local codes.
PROVISIONS FOR ADEQUATE COMBUSTION & VENTILATION AIR
