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6
AIR FOR COMBUSTION
AND VENTILATION
Continued
PROVIDING ADEQUATE
VENTILATION
The following are excerpts from
National Fuel
Gas Code, ANSI Z223.1/NFPA 54, Section 5.3, Air
for Combustion and Ventilation.
All spaces in homes fall into one of the three fol-
lowing ventilation classifications:
1. Unusually Tight Construction
2. Unconfined Space
3. Confined Space
The information on pages 5 through 7 will help
you classify your space and provide adequate ven-
tilation.
Unusually Tight Construction
The air that leaks around doors and windows may
provide enough fresh air for combustion and ven-
tilation. 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 ar-
eas such as joints around window and
door frames, between sole plates and
floors, between wall-ceiling joints, be-
tween 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 Space and Unconfined Space
The National Fuel Gas Code, ANSI Z223.1/NFPA
54
defines a confined space as a space whose vol-
ume 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 un-
confined 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 ap-
pliances installed in that space. Rooms communi-
cating directly with the space in which the appli-
ances are installed*, through openings not fur-
nished with doors, are considered a part of the
unconfined space.
* Adjoining rooms are communicating only if there
are doorless passageways or ventilation grills be-
tween 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 in-
stall 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. (vol-
ume of space)
If additional ventilation to adjoining room is sup-
plied 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
