C
OMBUSTION
AND
V
ENTILATION
A
IR
R
EQUIREMENTS
Warning: If the area in which
this appliance 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, Latest
Edition, Section 5.3 or
applicable local codes. This
appliance shall not be installed
in a confined space or unusually
tight construction unless
provisions are provided for
adequate combustion and
ventilation air.
Caution: Because water is a
product of fuel gas combustion,
all gas-fired appliances will
produce some water vapor
(humidity) when fired. The water
vapor may collect on windows
and walls, especially in
buildings constructed unusually
tight. Providing additional fresh
air will reduce the amount of
water vapor which collects on
the windows and walls.
9
This heater requires fresh air (oxygen) for proper combustion and
ventilation. In some cases, but not all, normal air infiltration into a building
will supply a sufficient amount of fresh air for proper combustion and
ventilation. The number of gas-fired appliances involved, the type of
space being utilized, and the construction tightness of the building
involved must all be considered when determining whether normal air
infiltration is sufficient or if additional fresh air will be needed for proper
combustion and ventilation of the gas-fired appliances installed in a
particular space.
Unconfined space and confined space are the terms used to describe
the space in which gas-fired appliances may be installed. The National
Fuel Gas Code , ANSI Z223.1/NFPA 54 defines a
confined space as a
space whose volume is less than 50 cubic feet per 1,000 Btu per hour
(4.8m
≈
per kW) of the aggregate input rating of all gas-fired appliances
installed in that space, and an
unconfined space as a space whose
volume is not less than 50 cubic feet per 1,000 Btu per hour (4.8m
≈
per
kW) of the aggregate input rating of all gas-fired appliances installed in
that space. Rooms communicating directly with the space in which the
appliances are installed, through openings not furnished with doors,
are considered a part of the to-be-defined space. For example, three
rooms in a house are adjoining with interconnecting passageways but
no doors; each room has an 8 foot ceiling. One room is 16 x 12 feet,
one is 12 x 12 feet, and one is 10 x 14 feet. The total volume of the
three rooms is 3,808 cubic feet; (8 x 16 x 12) plus (8 x 12 x 12) plus (8
x 10 x 14) equals 3,808 cubic feet. To be considered an unconfined
space in this example, the total maximum aggregate input rating of all
gas-fired appliances installed in the 3,808 cubic feet space must not
exceed 76,160 Btu per hour; (3,808 divided by 50) x 1,000 equals 76,160
Btu per hour.
Normal air infiltration into an unconfined space will be adequate to supply
the necessary fresh air for proper combustion and ventilation if the building
is not constructed unusually tight. However, if the building is of unusually
tight construction, additional fresh air from outside will be required for
proper combustion and ventilation of the gas-fired appliances installed
in the unconfined space. Unusually tight construction is defined as
construction where:
a. Walls and ceiling exposed to the outside atmosphere have a
continuous water vapor retarder with a rating of 1 perm (6 x 10
-11
kg per pa-sec-m˝) 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.
53D9013. Rev 1 03/03
