Duct System - Lennox ELITE Series Installation Instructions Manual

Duct System

Use industry‐approved standards (such as those pub­
lished by Air Conditioning Contractors of America or Ameri­
can Society of Heating, Refrigerating and Air Conditioning
Engineers) 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 - Do not operate the furnace in the heating mode
with an external static pressure that exceeds 0.5 inches
w.c. Higher external static pressures may cause erratic lim­
it operation.
Supply Air Plenum
If the furnace is installed without a cooling coil, a removable
access panel must be installed in the supply air duct. The
access panel should be large enough to permit inspection
(either by smoke or reflected light) of the heat exchanger
for leaks after the furnace is installed. The furnace access
panel must always be in place when the furnace is operat­
ing and it must not allow leaks into the supply air duct sys­
tem.
Return Air Plenum
NOTE - 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 de­
vice (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 re­
verse flow of the flue gas may result in incomplete combus­
tion and the formation of carbon monoxide gas. This toxic
gas might then be distributed throughout the house by the
furnace duct system.
In upflow applications, the 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 air­
tight seal between the bottom of the furnace and the plat­
form to ensure that the unit operates properly and safely.
Use fiberglass sealing strips, caulking, or equivalent seal­
ing 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.
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