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4
FRESH AIR FOR
COMBUSTION AND
VENTILATION
WARNING: If the area in which the heater may be operated does not meet the required volume for indoor combustion
air, combustion and ventilation air shall be provided by one of the methods described in the National Fuel
Gas Code, ANSI Z223.1/NFPA 54, the International Fuel Gas Code, or applicable local codes.
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
dened as construction where:
a. walls and ceilings exposed to
the outside atmosphere have a
continuous water vapor retarder
with a rating of one perm (6×10
-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 win-
dow and door frames, between sole
plates and oors, between wall-
ceiling joints, between wall panels, at
penetrations for plumbing, electrical,
and gas lines, and at other open-
ings. If your home meets all of
the three criteria above, you must
provide additional fresh air. See
Ventilation Air From Outdoors,
pages 5 and 6. If your home does
not meet all of the three criteria
above, see Determining Fresh-Air
Flow for Heater Location, page 4, 5
DETERMINING FRESH-AIR FLOW FOR HEATER LOCATION
Determining if you Have a Conned or Unconned Space*
Use this worksheet to determine if you have a conned or unconned space.
Space: Includes the room in which you will install heater plus any adjoining rooms with doorless passageways
or ventilation grills between the rooms.
1. Determine the volume of the space (length×width×height).
Length×Width×Height= cu.ft. (volume of space)
Example: Space size 20ft.(length)×16ft.( width)×8ft. (ceiling height)=2560cu. ft. (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. Divide the space volume by 50 cubic feet to determine the maximum Btu/Hr the space can support.
(volume of space)÷50 cu. ft.=(Maximum Btu/Hr the space can support)
Example: 2560 cu. ft. (volume of space)÷50 cu.ft.=51.2 or 51,200(maximum Btu/Hr the space can support)
PROVIDING ADEQUATE
VENTILATION
All spaces in homes fall into one of
the three following ventilation clas-
sications:
1. Unusually Tight Construction
2. Unconned Space
3. Conned Space
The information on pages 4
through 6 will help you classify
your space and provide adequate
ventilation.
WARNING: If the area in
which the heater may be operated
do e s n o t m eet th e r e qui r e d
volume for indoor combustion air,
combustion and ventilation air
shall be provided by one of the
methods described in the National
F u e l G a s C o d e , A N S I
Z 2 2 3 . 1 / N F P A 5 4 , t h e
International Fuel Gas Code, or
a p p l i c a b l e l o c a l c o d e s .
Conned and
Unconned Space
Conned space is a space whose
volume is less than 50 cubic feet
per 1,000 Btu per hour (4.8 m
3
per
kw) of the aggregate input rating
of all appliances installed in that
space and an unconned 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 aggregate 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 unconned space.
This heater shall not be in-
stalled in a conned space or
unusually tight construction unless
provisions are provided for
adequate combustion and
ventilation air.
* A d j o i n i n g r o o m s a r e
communicating only if there
are doorless passageways or
ventilation grills between them.
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