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113897-01A
6
AIR FOR COMBUSTION
AND VENTILATION
Continued
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 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 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. See
Ventilation Air From Outdoors
,
page 7.
If your home does not meet all of the three
criteria above, proceed to
Determining
Fresh-Air Flow For Fireplace Location
,
below.
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1
defines
a confined 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 aggregate input rating of all appli-
ances installed in that space and an unconfining
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 uncon-
fined space.
* Adjoining rooms are communicating only if
there are doorless
DETERMINING FRESH-AIR FLOW
FOR FIREPLACE LOCATION
Determining if You Have a Confined or
Unconfined Space
Use this work sheet to determine if you have a
confined or unconfined space.
Space:
Includes the room in which you will
install heater plus any adjoining rooms with door-
less passageways or ventilation grills between
the rooms.
1. Determine the volume of the space (length x
width x height).
Length x Width x Height =__________cu. ft.
(volume of space)
Example:
Space size 20 ft. (length) x 16 ft.
(width) x 8 ft. (ceiling height) = 2560 cu. 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. Multiply the space volume by 20 to determine
the maximum Btu/Hr the space can support.
__________ (volume of space) x 20 = (Maxi-
mum Btu/Hr the space can support)
Example:
2560 cu. ft. (volume of space) x 20 =
51,200 (maximum Btu/Hr the space can support)
3. Add the Btu/Hr of all fuel burning appliances in
the space.
Vent-free fireplace
___________ Btu/Hr
Gas water heater*
___________ Btu/Hr
Gas furnace
___________ Btu/Hr
Vented gas heater
___________ Btu/Hr
Gas fireplace logs
___________ Btu/Hr
Other gas appliances* + ___________ Btu/Hr
Total = ___________ Btu/Hr
* Do not include direct-vent gas appliances. Di-
rect-vent draws combustion air from the outdoors
and vents to the outdoors.
Example:
Gas water heater
__________ Btu/Hr
Vent-free fireplace
+ ________ Btu/Hr
Total = ________ Btu/Hr
4. Compare the maximum Btu/Hr the space can
support with the actual amount of Btu/Hr used.
_________Btu/Hr (maximum the space can support)
_________Btu/Hr (actual amount of Btu/Hr used)
Example:
51,200 Btu/Hr (maximum the space
can support)
56,000 Btu/Hr (actual amount of
Btu/Hr used)
30,000
26,000
56,000
