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GENERAL VENTING REQUIREMENTS AND
GUIDELINES
VENTING & COMBUSTION AIR REQUIREMENTS
This furnace removes both sensible and latent heat from
the combustion gases. Removal of latent heat results in
the condensation of flue gas water vapor. This condensed
water vapor drains from the secondary heat exchanger
and out of the unit into the drain trap.
When installed as a non-direct vent furnace, only exhaust
piping is required and inside combustion air may be used.
Refer to the section on "NON-DIRECT VENTING."
Direct vent installations require a dedicated combustion air
and venting system. All air for combustion is taken from
the outside atmosphere and all combustion products are
discharged to the outdoors.
Adequate facilities for providing air for combustion and
ventilation must be provided in accordance with Section
5.3, "Air for Combustion and Ventilation" of the National
Fuel Gas Code, ANSI Z223.1 (latest edition), in Canada
CSA B149.1; Canadian Natural Gas and Propane Installa-
tion Code and The National Fire Code of Canada, or appli-
cable provisions for the local building codes, and not
obstructed so as to prevent the flow of air to the furnace.
IMPORTANT: Air for combustion and ventilation must not
come from a corrosive atmosphere. Any failure due to cor-
rosive elements in the atmosphere is excluded from the
warranty coverage.
Combustion air must be free of acid-forming chemicals
such as sulfur, fluorine and chlorine. These elements are
found in aerosol sprays, detergents, bleaches, cleaning
solvents, air fresheners, paint and varnish removers, re-
frigerants and many other commercial and household
products. When burned in a gas flame, vapors from these
products form acid compounds. The acid compounds in-
crease the dew point temperature of the flue products and
are highly corrosive after they condense.
The following types of installations (but not limited to the
following) may require outdoor air for combustion (direct-
vent) due to chemical exposures:
-
Commercial buildings
-
Buildings with indoor pools
-
Furnaces installed in laundry rooms
-
Furnaces in hobby or craft rooms
-
Furnaces installed near chemical storage
areas
If combustion air is exposed to the following substances
(but not limited to the following), it should not be used and
the furnace may require outdoor air for combustion (direct-
vent).
-
Permanent wave solutions
-
Chlorinated waxes and cleaners
-
Chlorine-based swimming pool chemicals
-
Water softening chemicals
-
De-icing salts or chemicals
-
Carbon tetrachloride
-
Halogen type refrigerants
-
Printing inks, paint removers, varnishes etc.
-
Cleaning solvents (such as perchloroethylene)
-
Hydrochloric acid
-
Cements and glues
-
Antistatic fabric softeners for clothes dryers
-
Masonry curing and acid washing materials
Combustion air requirements are determined by whether
the furnace is in an open (unconfined) area or in a con-
fined space such as a closet or small room.
When the furnace is installed in the same space with other
gas appliances, such as a water heater, be sure there is
an adequate supply of combustion and ventilation air for
the furnace and the other appliances. Do not delete or re-
duce the combustion air supply required by the other gas
appliances in this space. See Z223.1, National Fuel Gas
Code (NFPA 54). In Canada B149.1; Canadian Natural
Gas and Propane Installation Code and The National Fire
Code of Canada for determining the combustion air re-
quirements for gas appliances. An unconfined space must
have at least 50 cubic feet (volume) for each 1,000 BTUH
of the total input of all appliances in the space. If the open
space containing the appliances is in a building with tight
construction (contemporary construction), outside air may
still be required for the appliances to burn and vent prop-
erly. Outside air openings should be sized the same as for
a confined space.
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