NOTE:Referto definitionsin sectiontitledUnusually Tight
Construction. If any one of the conditions apply, the space MUST
be considered confined space regardless of size.
1. Adjoining rooms can be considered part of an unconfined
area if there are openings without doors between rooms.
2. An attic or crawl space may be considered an unconfined
space provided there are adequate ventilation openings di-
rectly to outdoors. Openings MUST remain open and NOT
have any means of being closed off. Ventilation openings to
outdoors MUST be at least 1" square of free area per 4,000
BTUH of total input rating for all gas appliances in area.
3. Install air intake a minimum of 12" above maximum snow
level and clear of any obstruction. Duct or ventilation open-
ing requires one square inch of free area per 4,000 BTUH
of total input rating for all gas appliances in area.
4. Air inlet MUST be screened with not less than 1/4" mesh
screen.
UnusuallyTight Construction
In unconfined spaces, infiltration may be adequate to provide air
for combustion, ventilation and dilution of flue gases. However, in
buildings with unusually tight construction, additional air MUST
be provided using the methods described in section titled Con-
fined Space Installation:
Unusually tight construction is defined as: Construction with
2.
3.
Walls and ceilings exposed to the outside have a continu-
ous, sealed vapor barrier. Openings are gasketed or
sealed and
Doors and openable windows are weather stripped and
Other openings are caulked or sealed. These include joints
around window and door frames, between sole plates and
floors, between wall-ceiling joints, between wall panels, at
penetrations for plumbing, electrical and gas lines, etc.
VentilationAir
Some provincial codes and local municipalities require ventilation
or make-up air be brought into the conditioned space as replace-
ment air. Whichever method is used, the mixed return air temper-
ature across the heat exchanger MUST not fall below 60 °F or flue
gases will condense in the heat exchanger. This will shorten the
life of the heat exchanger and possibly void your warranty.
4. Vent and Combustion Air Piping
Poison carbon monoxide gas, fire and explo-
sion hazard,
Contaminated Combustion Air
Read and follow all instructions in this section,
Failure to properly vent this furnace can result in
death, personal injury and/or property damage.
Installations in certain areas or types of structures will increase
the exposure to chemicals or halogens that may harm the fur-
nace.
The following areas or types of structures may contain or have ex-
posure to the substances listed below. The installation must be
evaluated carefully as it may be necessary to provide outside air
for combustion.
SinglePipe(NgMP1Models)
This furnace is certified as a category IV appliance. This furnace
requires ventilation openings to provide air for proper combustion
and ventilation of flue gases. All duct or openings for supplying
combustion and ventilation air must comply with the gas codes or
in absence of local codes, the applicable national codes.
When the installation is complete, see the "Venting and Com-
bustion Air Check" in this manual.
DirectVent(NgMP2Models)
This furnace is certified as a category IV appliance. This furnace
uses outside air for combustion ONLY, it MUST be taken from the
same atmospheric pressure zone as the vent pipe. See Con-
fined Space Installation in the Combustion and Ventilation
Air in this manual.
DualCertified (*9MPDModels)
This furnace is certified as a category IV appliance. This furnace
can be installed as a direct vent furnace using outside air for com-
bustion or the furnace can use air from inside the structure for
combustion. The INLET air pipe is optional. If combustion air
comes from inside the structure, adequate make up air MUST be
• Commercial buildings.
• Buildings with indoor pools.
• Furnaces installed in laundry rooms.
• Furnaces installed in hobby or craft rooms.
• Furnaces installed near chemical storage areas.
• Permanent wave solutions for hair.
• Chlorinated waxes and cleaners.
• Chlorine based swimming pool chemicals.
• Water softening chemicals.
• De-icing salts or chemicals.
• Carbon tetrach!oride.
• Halogen type refrigerants.
• Cleaning solvents (such as perch!oroethylene).
• Printing inks, paint removers, varnishes, etc.
• Hydrochloric acid.
• Sulfuric Acid.
• Solvent cements and glues.
• Antistatic fabric softeners for clothes dryers.
• Masonry acid washing materials.
provided to compensate for oxygen burned. See Confined
Space Installation in the Combustion and Ventilation Air
chapter, if combustion air is drawn from outside the structure, it
MUST be taken from the same atmospheric pressure zone as the
vent pipe.
Ventand Combustion Air PipingGuidelines
NOTE: All vent piping MUST be installed in compliance with local
codes or ordinances, these instructions, good trade practices,
and codes of country having jurisdiction.
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