441 01 2314 06
Specifications are subject to change without notice.
19
Duct Design
Design and install the air distribution system to comply with Air
Conditioning Contractors of America manuals or other approved
methods that conform to local codes and good trade practices.
When the furnace is located in an area near or adjacent to the living
area, the system should be carefully designed with returns to mini-
mize noise transmission through the
supply and return air grilles.
Any blower moving a high volume of air will produce audible noise
which could be objectionable when the unit is located very close to
a living area. It is often advisable to route the supply air ducts un-
der the floor and return air ducts through the attic.
•
Refer to furnace Technical Support Manual (Blower Data) for
airflow information.
•
Size ductwork to handle airflow for heating and air conditioning
if used.
Duct Installation Requirements
•
When a furnace is installed so that supply ducts carry air circu-
lated by the furnace to areas outside of the space containing
the furnace, the return air shall also be handled by duct(s)
sealed to the furnace casing and terminating outside the space
containing the furnace.
CARBON MONOXIDE POISONING HAZARD
Failure to follow this warning could
result in personal injury or death.
Install cooling coil on furnace discharge. Cool air
passing over heat exchanger could cause
condensate to form resulting in heat exchanger
failure.
!
WARNING
•
When the furnace is used with a cooling unit, the furnace shall
be installed parallel with or on the upstream side of the cooling
unit to avoid condensation in the heating element.
•
With a parallel flow arrangement, the dampers or other means
used to control flow of air shall be adequate to prevent chilled
air from entering the furnace. Chilled air going through the fur-
nace could cause condensation and shorten furnace life.
Dampers (purchased locally) can be either automatic or manu-
al. Manually or automatically operated dampers MUST be
equipped with a means to prevent furnace or air conditioning
operation, unless damper is in the full heat or cool position
•
Installation of locking
−
type dampers is recommended in all
branches, or in individual ducts to balance system’s air flows.
•
Non
−
combustible, flexible duct connectors are recommended
for return and supply connections to furnace.
•
If air return grille is located close to the fan inlet, install at least
one, 90
°
air turn between fan and inlet grille to reduce noise.
•
Ductwork installed in attic, or exposed to outside temperatures
requires a minimum of 2
″
(50.8mm) of insulation with outdoor
type vapor barrier.
•
Ductwork installed in an indoor unconditioned space requires
a minimum of 1
″
(25.4mm) of insulation with indoor type vapor
barrier.
Inspection Panel on Some Models
For a furnace not equipped with a cooling coil, the outlet duct shall
be provided with a removable access panel. This opening shall be
accessible when the furnace is installed and shall be of such a size
that the heat exchanger can be viewed for possible openings using
light assistance or a probe can be inserted for sampling the air
stream. This access cover shall be attached in such a manner as
to prevent air leaks.
Sub-Bases for Combustible Floors - Furnace Only
The Subbase for Combustible Floors
MUST
be used when a
downflow furnace is set on a combustible floor, even when the fur-
nace is installed on a coil box.
NOTE:
Supply opening is 3
7
/
8
″
(98.4mm) from the rear of the fur-
nace. Therefore maintain a 3
7
/
8
″
(98.4mm) clearance from a wall
behind the furnace (where applicable).
1. Cut the opening in the floor according to the dimensions in
Table 4
because the base is equipped with locating tabs that
center the base over the opening.
The opening in the base is 1
1
/
4
″
(31.75mm) shorter and 1
1
/
8
″
(28.58mm) narrower than the minimum required size of the
opening in the floor. This is done to maintain a 1
″
(25.4mm)
clearance between the floor and the plenum.
2. Fabricate the plenum to the dimensions given in
Table 4
. Note
that the dimensions given are outside dimensions.
3. Set the base over the opening in the floor, centering the open-
ing in the base over the opening in the floor. Fasten the base to
the floor with screws or nails. See
Figure 13
and
Figure 14.
4. Drop the plenum through the opening in the base. The flange
of the plenum should rest on top of the combustible floor base.
