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7
AIR FOR COMBUSTION AND VENTILATION
Confined and Unconfined Space
The
National Fuel Gas Code, ANSI Z223.1/NFPA 54
allows two meth-
ods for determining whether the space in which the heater is being
installed is confined or unconfined. The standard method defines a
confined space as a space whose volume is less than 50 cubic feet
per 1,000 Btu per hour (4.8 m3 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 m3 per kw) of the aggregate input rating of all appli-
ances 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.
Where the air infiltration of a structure is known, the Known Air
Infiltration Rate Method may be used. Follow the
National Fuel Gas
Code, ANSI Z223.1/NFPA 54
to use this method to determine if the
space is confined or unconfined.
* Adjoining rooms are communicating only if there are doorless
passageways or ventilation grills between them.
DETERMINING FRESH-AIR FLOW FOR FIREBOX LOCATION
Determining if You Have a Confined or Unconfined Space using
the standard method
Use this work sheet to determine if you have a confined or uncon-
fined space.
Space:
Includes the room in which you will install heater plus any
adjoining rooms with doorless passageways or ventilation grills be-
tween 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 22 ft. (length) x 18 ft. (width) x 8 ft. (ceiling
height) = 3,168 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:
3,168 cu. ft. (volume of space) x 20 = 63,360 (maximum
Btu/Hr 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 40,000 Btu/Hr
Vent-free fireplace + 39,000 Btu/Hr
Total
= 79,000 Btu/Hr
WARNING: This heater shall not be installed in a
room or space unless the required volume of indoor
combustion air is provided by the method described
in the
National Fuel Gas Code, ANSI Z223.1/NFPA 54,
the
International Fuel Gas Code,
or applicable local
codes. Read the following instructions to ensure proper
fresh air for this and other fuel-burning appliances in
your home.
Today’s homes are built more energy efficient than ever. New materials,
increased insulation and new construction methods help reduce heat
loss in homes. Home owners weather strip and caulk around windows
and doors to keep the cold air out and the warm air in. During heating
months, home owners want their homes as airtight as possible.
While it is good to make your home energy efficient, your home ne eds
to breathe. Fresh air must enter your home. All fuel-burning appliances
need fresh air for proper combustion and ventilation.
Exhaust fans, fireplaces, clothes dryers and fuel burning appliances
draw air from the house to operate. You must provide adequate fresh
air for these appliances. This will ensure proper venting of vented
fuel-burning appliances.
PROVIDING ADEQUATE VENTILATION
The following are excerpts from
National Fuel Gas Code, ANSI
Z223.1/NFPA 54, Air for Combustion and Ventilation
.
All spaces in homes fall into one of the three following ventilation
classifications:
1. Unusually Tight Construction
2. Unconfined Space
3. Confined Space
The information on pages 8 through 10 will help you classify your space
and provide adequate ventilation.
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 outside 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, be-
tween 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 10.
If your home does not meet all of the three criteria above, proceed
to
Determining Fresh-Air Flow For Firebox Location
.
