Useindustry-approvedstandardsto sizeandinstallthe
supplyandreturnairductsystem.Thiswillresultinaquiet
andlow-staticsystemthathasuniformairdistribution.
NOTE - Operation of this furnace in heating mode (indoor
blower operating at selected heating speed) with an exter-
nal static pressure which exceeds O.8 inches w.c. may re-
sult 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 al-
ways be in place when the furnace is operating and it must
not allow leaks into the supply air duct system.
Return Air Plenum
Return air must not be drawn from a room where this
furnace, or any other gas appliance (ie., a water heat-
er), 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 prod-
ucts can be pulled back down the vent pipe and into the
room. This reverse flow of the flue gas may result in incom-
plete 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.
All pipe, fittings, primer and solvent cement must conform
with American National Standard Institute and the Ameri-
can Society for Testing and Materials (ANSI/ASTM) stan-
dards. The solvent shall be free flowing and contain no
lumps, undissolved particles or any foreign matter that ad-
versely affects the joint strength or chemical resistance of
the cement. The cement shall show no gelation, stratifica-
tion, or separation that cannot be removed by stirring. Re-
fer to the table 4 below for approved piping and fitting mate-
rials.
CAUTION
TABLE 4
PIPING AND FITTINGS SPECIFICATIONS
ASTM
PIPE & FITTING MATERIAL SPECIFICATION
Schedule 40 PVC (Pipe) D1785
Schedule 40 PVC (Cellular Core Pipe) F891
Schedule 40 PVC (Fittings) D2466
SDR-21PVC (Pipe) D2241
SDR-26 PVC (Pipe) D2241
Schedule 40 ABS Cellular Core DWV (Pipe) F628
Schedule 40 ABS (Pipe) D1527
Schedule 40 ABS (Fittings) D2468
ABS-DWV (Drain Waste & Vent) D2661
(Pipe & Fittings)
PVC-DWV (Drain Waste & Vent) D2665
Pipe & Fittings)
Primers and solvents must meet ASTM specifications.
PVC primer is specified in ASTM F 656. Use PVC solvent
cement as specified in ASTM D 2564 and ABS solvent ce-
ment as specified in ASTM D 2235. Low temperature sol-
vent cement is recommended. Metal or plastic strapping
may be used for vent pipe hangers.
When making ABS joints, pieces can be prepared with a
cleaner. When joining ABS to PVC materials, use PVC sol-
vent cement. Refer to the procedure specified in ASTM
D3138.
Canadian Applications Only - Pipe, fittings, primer and sol-
vent cement used to vent this appliance must be certified to
ULC $636 and supplied by a single manufacturer as part of
an approved venting system. When bonding the vent sys-
tem to the furnace, use ULC S636 approved One-Step
Transition Cement to bond the pipe to the flue collar, 90°
elbow or reducing 90 °elbow as applicable. In addition, the
first three feet of vent pipe from the furnace flue collar must
be accessible for inspection.
Table 5 lists the available exhaust termination kits, as well
as vent pipe equivalencies which must be used when sizing
vent pipe. All Lennox vent terminations are PVC or ABS.
Page 17
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