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123639-01D
7
AIR FOR COMBUSTION AND VENTILATION
Continued
40,000
31,500
71,500
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
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 8.
If your home does not meet all of the three
criteria above, proceed to
Determining
Fresh-Air Flow For Heater Location
.
Confined Space 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/hr (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/hr (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 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 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.
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 space can support)
_____ Btu/Hr (actual amount used)
Example:
51,200 Btu/Hr (maximum the
space can support)
79,000 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 additional fresh air. Your options are
as follows:
A.
Rework worksheet, adding the space of an
adjoining 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 8.
B. Vent room directly to the outdoors. See
Ventilation Air From Outdoors
, page 8.
C.
Install a lower Btu/Hr fireplace, if lower
Btu/Hr size makes room unconfined.
If the actual Btu/Hr used is less than the maxi-
mum Btu/Hr the space can support,
the space is
an unconfined space. You will need no additional
fresh air ventilation.
