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10
Combustion and Ventilation Air Requirements
(d) In addition to air needed for combustion, air shall be supplied for
ventilation, including all air required for comfort and proper
working conditions for personnel.
(e) While all forms of building construction cannot be covered in
detail, air for combustion, ventilation and dilution of flue gases
for gas utilization equipment vented by natural draft normally
may be obtained by application 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.
Space, Unconfined.
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 installed in that space. Rooms communicating di-
rectly with the space in which the appliances are installed through
openings not furnished with doors, are considered a part of the
unconfined space.
WARNING
Possible death, personal injury or property damage may occur if the furnace is not provided with enough fresh air
for proper combustion and ventilation of flue gases. Most homes require outside air to be supplied to the furnace
area.
The following information on air for combustion and ventilation
is reproduced from the
National Fuel Gas Code
NFPA 54/ANSI Z223.1 Section 5.3.
5.3.1 General:
(a) The provisions of 5.3 apply to gas utilization equipment in-
stalled in buildings and which require air for combustion,
ventilation and dilution of flue gases from within the building.
They do not apply to (1) direct vent equipment which is
constructed and installed so that all air combustion is obtained
from the outside atmosphere and all flue gases are discharged to
the outside atmosphere, or (2) enclosed furnaces which incor-
porate 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 temperature 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 compressors.
Improved construction and additional insulation in buildings have reduced heat loss by reducing air filtration and escape
around doors and windows. These changes have helped in reducing heating/cooling costs but have created a problem
supplying combustion and ventilation air for gas fired and other fuel burning appliances. Appliances that pull air out of
the house (clothes dryers, exhaust fans, fireplaces, etc.) increase the problem by starving appliances for air.
House depressurization can cause back drafting or improper combustion of gas-fired appliances, thereby exposing
building occupants to gas combustion products that could include carbon monoxide.
If this furnace is to be installed in the same space with other gas appliances, such as a water heater, ensure there is an
adequate supply of combustion and ventilation air for the other appliances. Refer to the latest edition of the National Fuel
Gas Code NFPA 54/ANSI Z223.1 (Section 5.3), or CSA B149 Installation Codes (Sections 7.2, 7.3, or 7.4), or applicable
provisions of the local building codes for determining the combustion air requirements for the appliances.
This furnace must use indoor air for combustion. It cannot be installed as a direct vent (i.e., sealed combustion) furnace.
The burner box is present only to help reduce sound transmission from the burners to the occupied space.
Most homes will require outside air be supplied to the furnace area by means of ventilation grilles or ducts connecting
directly to the outdoors or spaces open to the outdoors such as attics or crawl spaces.
