AIR FOR COMbUSTION
AND VENTILATION
Continued
Unusually Tight Construction
The air that leaks around doors and windows
may provide enough fresh air for combustion and
ventilation. 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 (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 (a,b, and c, 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
passageways 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) = 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 =
(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 appliances
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
40,000
33,000
73,000
