19
Rev. 0
COMBUSTION AND VENTILATION AIR
(DIRECT/NON-DIRECT VENT MODELS)
WARNING
Property damage, bodily injury, or death may occur if
the furnace and any other fuel-burning appliances are
not provided with enough fresh air for proper combus-
tion and ventilation of flue gases. Most homes require
outside air to be supplied into the furnace area.
Improved construction and additional insulation in homes
has reduced the heat loss and made these homes much
tighter around doors and windows so that air infiltration is
minimal. This creates a problem to supply combustion and
ventilation air for gas fired or other fuel burning appliances..
Any use of appliances that pull air out of the house (clothes
dryers, exhaust fans, fireplaces, etc.) increases this prob-
lem and appliances could be starving for air.
In addition, these energy saving measures mean that your
home will retain more water vapor and have a higher rela-
tive humidity. High humidity, especially during cold weather,
may be damaging to buildings because condensation forms
on windows and inside walls.
AIR REQUIREMENTS
Most homes will require that outside air be supplied to the
furnace area by means of ventilation grilles or ducts con-
necting directly to the outdoors or spaces open to the out-
doors such as attics or crawl spaces. The following infor-
mation on air for combustion and ventilation is reproduced
from the National Fuel Gas Code NFPA54/ANSIZ223.1 Sec-
tion 5.3.
5.3.1 General
(a) The provisions of 5.3 apply to gas utilization equipment
installed in buildings and which require air for combustion,
ventilation and dilution of flue gases from within the build-
ing. They do not apply to (1) direct vent equipment which is
constructed and installed so that air for combustion is ob-
tained from the outside atmosphere and all flue gases are
discharged to the outside atmosphere, or (2) enclosed fur-
naces which incorporate an integral total enclosure and use
only outside air for combustion and dilution of flue gases.
(b) Equipment shall be installed in a location in which the
facilities for ventilation permit satisfactory combustion of
gas, proper venting, and the maintenance of ambient tem-
perature at safe limits under normal conditions of use.
Equipment shall be located so as not to interfere with proper
circulation of air. When normal infiltration does not provide
the necessary air, outside air shall be introduced.
(c) In addition to air needed for combustion, process air
shall be provided as required for: cooling of equipment or
material, controlling dew point, heating, drying, oxidation
or dilution, safety exhaust, odor control, and air for com-
pressors.
(d) In addition to air needed for combustion, air shall be
applied for ventilation, including all air required for comfort
and proper working conditions for personnel.
(e) While all forms of building construction cannot be cov-
ered in detail, air for combustion, ventilation, and dilution of
flue gases for gas utilization equipment vented by natural
draft normally may be obtained by appliance of one of the
methods covered in 5.3.3 and 5.3.4.
(f) Air requirements for the operation of exhaust fans,
kitchen ventilation systems, clothes dryers, and fireplaces
shall be considered in determining the adequacy of a space
to provide combustion air requirements.
5.3.2 Equipment Located in Unconfined Spaces:
In unconfined spaces (see definition below) in buildings,
infiltration may be adequate to provide air for combustion,
ventilation and dilution of flue gases. However, in buildings
of tight construction (for example, weather stripping, heavily
insulated, caulked, vapor barrier, etc.), additional air may
need to be provided using the methods described in 5.3.3-
b or 5.3.4.
Unconfined Space. For purposes of this Code, a space
whose volume is not less than 50 cubic feet per 1,000 Btu
per hour of the aggregate input rating of all appliances in-
stalled 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.
5.3.3 Equipment Located in Confined Spaces:
(a)
All Air from Inside the Building: The confined space shall
be provided with two permanent openings communicating
directly with an additional room(s) of sufficient volume so
that the combined volume of all spaces meets the criteria
for an unconfined space. The total input of all gas utiliza-
tion equipment installed in the combined space shall be
considered in making this determination. Each opening shall
have a minimum free area of 1 square inch per 1,000 Btu
per hour of the total input rating of all gas utilization equip-
ment in the confined space, but not less than 100 square
inches. One opening shall be within 12 inches of the top
and one within 12 inches of the bottom of the enclosure.
The following drawing illustrates the air opening specifica-
tions for equipment located in confined spaces; all air from
inside building.
