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6
Unusually Tight Construction
The air that leaks around doors and windows may
provide enough fresh air for combustion and ven-
tilation. 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 (6x10
-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 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 Heater Location
.
Confined and Unconfined Space
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 un-
confined 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 HEATER 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 doorless pas-
sageways 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) = 2,560 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:
2,560 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)
79,000 Btu/Hr (actual amount of
Btu/Hr used)
40,000
+ 39,000
= 39,000