12
If outside air is used as return air to the furnace
for ventilation or to improve indoor air quality, the
system must be designed so that the return air
is not less than 50° F (10° C) during operation.
If a combination of indoor and outdoor air is used,
the ducts and damper system must be designed
so that the return air supply to the furnace is
equal to the return air supply under normal,
indoor return air applications.
When a cooling system is installed which uses
the furnace blower to provide airflow over the
indoor coil, the coil must be installed downstream
(on the outlet side) of the furnace or in parallel
with the furnace.
If a cooling system is installed in parallel with the
furnace, a damper must be installed to prevent
chilled air from entering the furnace and
condensing on the heat exchanger. If a manually
operated damper is installed, it must be designed
so that operation of the furnace is prevented
when the damper is in the cooling position and
operation of the cooling system is prevented
when the damper is in the heating position.
Return Air
In applications where the supply ducts carry
heated air to areas outside the space in which
the furnace is installed, the return air must be
delivered to the furnace by duct(s) sealed to the
furnace casing, running full size and without
interruption.
!
WARNING:
The solid base of these furnaces must be
in place when the furnace is installed with
side return air ducts. Removal of all or part
of the base could cause products of
combustion to be circulated into the living
space and create potentially hazardous
conditions, including carbon monoxide
poisoning that could result in personal
injury or death.
The return air ductwork may be connected to
any or all of the following: left side return, right
side return, or bottom return. NOTE: Do not
use the back of the furnace for return air.
Table 2, in the front pages of these instructions,
contains the airflow data for each furnace model.
Where maximum airflow is 1800 CFM or more,
two openings must be used for return air.
!
WARNING:
Products of combustion must not be
allowed to enter the return air ductwork
or the circulating air supply. Failure to
prevent products of combustion from
being circulated into the living space can
create potentially hazardous conditions
including carbon monoxide poisoning
that could result in personal injury or
death.
All return ductwork must be secured to
the furnace with sheet metal screws. For
installations in confined spaces, all return
ductwork must be adequately sealed
and joints must be taped. When return air
is provided through the bottom of the
furnace, the joint between the furnace
and the return air plenum must be air
tight.
The floor or platform on which the furnace
is mounted must provide sound physical
support of the furnace with no gaps,
cracks, or sagging between the furnace
and the floor or platform.
Return air and circulating air ductwork
must not be connected to any other heat
producing device such as a fireplace
insert, stove, etc. Doing so may result in
fire, explosion, carbon monoxide
poisoning, personal injury, or property
damage.
GAS SUPPLY AND PIPING
!
CAUTION:
Do not re-drill the burner orifices. If the
orifice size must be changed, use only
new orifices.
