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119315-01D
7
The air that leaks around doors and windows
may provide enough fresh air for combus-
tion 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 these three
criteria, you must provide additional
fresh air. See
Ventilation Air From
Outdoors
, page 8.
If your home does not meet all of the
three criteria above, proceed to
Deter-
mining Fresh-Air Flow For Fireplace
Location
.
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/
NFPA 54
defines a confined space as a
space whose volume is less than 50 ft
3
per
1,000 Btu/hr (4.8 m
3
/kw) of the aggregate
input rating of all appliances installed in that
space and an unconfined space as a space
whose volume is not less than 50 ft
3
per
1,000 Btu/hr (4.8 m
3
/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
unconfined space.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation
grills between them.
aiR FoR CoMBUsTioN
aND VENTilaTioN
Continued
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
fireplace 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 16 ft. (length) x 14 ft.
(width) x 8 ft. (ceiling height) = 1792 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:
1792 cu. ft. (volume of space) x 20
= 35,840 (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.
Direct-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:
35,840 Btu/Hr (maximum the
space can support)
40,000 Btu/Hr (actual amount of
Btu/Hr used)
30,000
10,000
40,000
