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Duct System
Use industry approved standards to size and install the
supply and return air duct system. This will result in a quiet
and low static system that has uniform air distribution.
NOTE: Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an
external static pressure that exceeds 0.8 inches w.c. may
result in erratic limit operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel should be installed in the supply air duct. The
access panel should be large enough to permit inspection
(by reflected light) of the heat exchanger for leaks after
the furnace is installed. If present, this access panel must
always be in place when the furnace is operating and it
must not allow leaks into or from the supply air duct system.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas fueled appliance (i.e., water
heater), or carbon monoxide producing device (i.e., wood
fireplace) is installed. When return air is drawn from a
room, a negative pressure is created in the room. If a gas
appliance is operating in a room with negative pressure, the
flue products can be pulled back down the vent pipe and
into the room. This reverse flow of the flue gas may result
in incomplete combustion and the formation of carbon
monoxide gas. This toxic gas might then be distributed
throughout the house by the furnace duct system.
Return air can be brought in through the bottom or either
side of the furnace. If a furnace with bottom return air is
installed on a platform, make an airtight seal between the
bottom of the furnace and the platform to ensure that the
unit operates properly and safely. Use fiberglass sealing
strips, caulking, or equivalent sealing method between the
plenum and the furnace cabinet to ensure a tight seal. If
a filter is installed, size the return air duct to fit the filter
frame.
Pipe and Fittings Specifications
All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the American
Society for Testing and Materials (ANSI/ASTM) standards.
The solvent shall be free flowing and contain no lumps,
undissolved particles or any foreign matter that adversely
affects the joint strength or chemical resistance of the
cement. The cement shall show no gelation, stratification,
or separation that cannot be removed by stirring. Refer to
Table 2 for approved piping and fitting materials.
507028-03
Piping and Fittings Specifications
Schedule 40 PVC (Pipe)
Schedule 40 PVC (Cellular Core Pipe)
Schedule 40 PVC (Fittings)
Schedule 40 CPVC (Pipe)
Schedule 40 CPVC (Fittings)
SDR-21 PVC or SDR-26 PVC (Pipe)
SDR-21 CPVC or SDR-26 CPVC (Pipe)
Schedule 40 ABS Cellular Core DWV
(Pipe)
Schedule 40 ABS (Pipe)
Schedule 40 ABS (Fittings)
ABS-DWV (Drain Waste & Vent)
(Pipe & Fittings)
PVC-DWV (Drain Waste & Vent)
Pipe & Fittings)
Primer & Solvent Cement
PVC & CPVC Primer
PVC Solvent Cement
CPVC Solvent Cement
ABS Solvent Cement
PVC/CPVC/ABS All Purpose Cement For
Fittings & Pipe of the same material
ABS to PVC or CPVC Transition Solvent
Cement
Canada Pipe & Fitting & Solvent
Cement
PVC & CPVC Pipe and Fittings
PVC & CPVC Solvent Cement
ABS to PVC or CPVC Transition Cement
Polypropylene Venting System
PolyPro® by Duravent
InnoFlue® by Centrotherm
ECCO Polypropylene Vent
Issue 1809
D1785
F891
D2466
F441
F438
D2241
F442
F628
D1527
D2468
D2661
D2665
ASTM
Specification
F656
D2564
F493
D2235
D2564, D2235,
F493
D3138
Marking
ULCS636
ULC-S636
ULC-S636
ULC-S636
TM
Table 2.
Page 11 of 66
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