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900719-00C
7
Unusually tight construction is defi ned as
construction where:
a. walls and ceilings exposed to the out-
side atmosphere have a continuous
water vapor retarder with a rating of one
perm (6 x 10
-11
kg per pa-sec-m
2
) 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 fl oors, between wall-ceiling joints,
between wall panels, at penetrations for
plumbing, electrical, and gas lines, and
at other openings.
If your home meets all three criteria above,
you must provide additional fresh air. See
Ventilation Air From Outdoors, Page 9.
If your home does not meet all three criteria
above, proceed to Determining Fresh-Air
Flow For Heater Location.
Confi ned and Unconfi ned Space
The National Fuel Gas Code, ANSI Z223.1/
NFPA54
allows two methods for determining
whether the space in which the heater is being
installed is con
fi
ned or uncon
fi
ned space. The
standard method de
fi
nes a con
fi
ned space as a
space whose volume is less than 50 cubic feet
per 1,000 Btu per hour (4.8 m
3
per kw) of the ag-
gregate input rating of all appliances installed in
that space and an uncon
fi
ned space as a space
whose volume is not less than 50 cubic feet per
1,000 Btu per hour (4.8 m
3
per kw) of the ag-
gregate input rating of all 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 uncon
fi
ned space.
Where the air in
fi
ltration rate of a structure is
known, the Known Air In
fi
ltration Rate Method
may be used. Follow The National Fuel Gas
Code, ANSI Z223.1/NFPA 54 to use this
method to determine if the space is con
fi
ned
or uncon
fi
ned.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grills between them.
DETERMINING FRESH-AIR FLOW
FOR FIREPLACE LOCATION
Determining if You Have a Confi ned or
Unconfi ned Space Using the Standard
Method
AIR FOR COMBUSTION AND VENTILATION
Today’s homes are built more energy ef
fi
cient
than ever. New materials, increased insulation,
and new construction methods help reduce
heat loss in homes. Homeowners apply
weather strip and caulk around windows and
doors to keep the cold air out and the warm air
in. During heating months, homeowners want
their homes as airtight as possible.
While it is good to make your home energy
ef
fi
cient, your home needs to breathe. Fresh
air must enter your home. All fuel-burning ap-
pliances need fresh air for proper combustion
and ventilation.
Exhaust fans, some
fi
replaces, clothes dryers
and some fuel-burning appliances draw air
from the house to operate. You must provide
adequate fresh air for these appliances. This
will ensure proper venting of vented fuel-
burning appliances.
PROVIDING ADEQUATE
VENTILATION
The following are excerpts from
National Fuel
Gas Code, ANSI Z223.1/NFPA 54, Air for
Combustion and Ventilation.
All spaces in homes fall into one of the three
following ventilation classi
fi
cations:
1. Unusually
Tight
Construction
2. Uncon
fi
ned Space
3. Con
fi
ned Space
The information on
Pages 7–9
will help you
classify your space and provide adequate
ventilation.
Unusually Tight Construction
The air that leaks around doors and windows
may provide enough fresh air for combustion
and ventilation. However, in buildings of un-
usually tight construction, you must provide
additional fresh air.
WARNING: This heater shall not
be installed in a room or space un-
less the required volume of indoor
combustion air is provided by the
method described in the National
Fuel Gas Code, ANSI Z223.1/NFPA
54, the International Fuel Gas Code,
or applicable local codes. Read the
following instructions to ensure
proper fresh air for this and other fuel-
burning appliances in your home.
