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113110-01A
7
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 ar-
eas such as joints around window and
door frames, between sole plates and
floors, between wall-ceiling joints, be-
tween wall panels, at penetrations for
plumbing, electrical, and gas lines, and
at other openings.
If your home meets all of these three crite-
ria, 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
Determining Fresh-
Air Flow For Fireplace Location, below.
Confined and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/NFPA
54 defines a confined space as a space whose vol-
ume 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 un-
confined 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 ap-
pliances installed in that space. Rooms communi-
cating directly with the space in which the appli-
ances are installed*, through openings not fur-
nished with doors, are considered a part of the
unconfined space.
* Adjoining rooms are communicating only if there
are doorless passageways or ventilation grills be-
tween 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 in-
stall fireplace plus any adjoining rooms with
doorless 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. (vol-
ume of space)
If additional ventilation to adjoining room is sup-
plied 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. 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:
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
