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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 plumb
-
ing, 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/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 ag-
gregate 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 un-
confined 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 passageways 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 deter-
mine the maximum Btu/Hr the space can
support.
(volume of space) x 20 = (maximum 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 appli-
ances in the space.
Vent-free heater
_______ 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 heater
+ ______ 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)
70,000 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 maximum Btu/Hr the space can sup-
port. You must provide additional fresh air.
40,000
30,000
70,000
