# 45465K005
Page 12
Figure 16
Optional Outside Air
Gas
Water
Heater
Soffit
Vents
Joist and Insulation
Gas
Furnace
Gable Vent
16 Min.
”
important that the inlet terminate in the attic 12" above
the ceiling joist or attic insulation, which ever is the
highest. It is required that the attic have proper
ventilation so that adequate combustion air be avail-
able. If ventilation is not provided, the furnace may not
operate properly.
3.
An additional method for bringing combustion air to the
furnace is shown in Figure 16. A single 2" or 3" plastic
(PVC) drain pipe, schedule 40 PVC, ABS, single wall
galvanized, or single wall stainless steel inlet pipe (see
Table 1 on page 11) can be installed from the furnace
through the roof terminating at the same height as the
vent. These pipes should be installed no closer than
16". A 180° elbow must be installed on the inlet pipe to
prevent rain and snow from entering the pipe. The
actual height of the roof termination should be 12"
above the average recorded snow accumulation.
Existing Venting Systems
When an existing Category I furnace is removed or
replaced, the original venting system may no longer be
sized to properly vent the attached appliances. An improp-
erly sized venting system can result in spillage of flue
products into the living space, the formation of conden-
sate, leakage, etc. See the
WARNING
box on page 13 for
proper test procedure.
Circulating Air Supply
When the furnace is installed so that the supply ducts
carry air circulated by the furnace to areas outside the
space containing the furnace, the return air shall be
handled by a duct or ducts sealed to the furnace casing
Joist and Insulation
Soffit
Vents
Gas
Water
Heater
Gas
Furnace
Gable Vent
12” Min.
Attic Must Be
Well Ventilated
Note:
Optional Attic Inlet Air
Figure 15
and terminated outside the space containing the furnace.
A return air duct system is recommended. If the unit is
installed in a confined space or closet, a return connection
must be run, full size, to a location outside the closet. The
air duct in the closet must be tight to prevent any entrance
of air from the closet into the circulating air.
If there is no complete return air duct system, the return air
connection must be sealed to furnace casing and run, full
size, to a location outside the utility room or space housing
furnace to prevent a negative pressure on venting system.
When installing a CAM coil in a horizontal position with a
horizontal gas furnace, always keep the open end of the
A-coil
facing the supply air outlet
of the furnace (blow into
the open end of the A-coil). The A-coil should
point away
from the supply air outlet
of the furnace (see Figure 17).
If a cooling coil is not installed with the furnace, then a
removable access panel should be provided in the supply
plenum for purposes of inspecting the heat exchanger.
This opening shall be accessible when the furnace is
installed, and shall be of such size that the heat ex-
When an air conditioning unit is used in
conjunction with the furnace, the evaporator
coil must be installed in the discharge (sup-
ply) air. Do not install an evaporator coil in
the return air; excessive condensation will
occur within the furnace.
CAUTION
