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110361-01F
6
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 cri
-
teria, 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.
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 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 unconfined
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 unconfined space.
* Adjoining rooms are communicating only if
there are doorless passageways or ventilation grills
between them.
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
heater plus any adjoining rooms with doorless pas-
sageways or ventilation grills between the rooms.
AIR FOR COMBUSTION
AND VENTILATION
Continued
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)
The space in the above example is a confined space
because the actual Btu/Hr used is more than the maxi
-
mum Btu/Hr the space can support. You must provide
additional fresh air. Your options are as follows:
A. Rework worksheet, adding the space of an adjoin
-
ing room. If the extra space provides an unconfined
space, remove door to adjoining room or add
ventilation grills between rooms. See Ventilation
Air From Inside Building, page 7.
B. Vent room directly to the outdoors. See Ventila
-
tion Air From Outdoors, page 7.
C. Install a lower Btu/Hr heater, if lower Btu/Hr size
makes room unconfined.
30,000
26,000
56,000