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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 Heater 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 com
-
municating 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.
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.
(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:
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)
73,000 Btu/Hr (actual amount of
Btu/Hr used)
The space in the example is a confined space because
the actual Btu/Hr used is more than the maximum
Btu/Hr the space can support. You must provide ad
-
ditional 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 fireplace, if lower Btu/Hr
size makes room unconfined.
AIR FOR COMBUSTION
AND VENTILATION
Continued
40,000
33,000
73,000
