7
NEGATIVE
PRESSURE IN
BASEMENT
RETURN AIR IS VERY IMPORTANT
When installing this furnace, return air MUST BE incorporated
into the system. Return air can be provided by installing a sepa-
rate duct system or by tying into the cold air return of an existing
gas or oil furnace. Th
e cold air return duct can be connected to
the furnace with either a factory manufactured U. S. Stove fi l-
ter box, model UFB908 or an equivalent fabricated from sheet
metal.
When installing a cold air return, the minimum size shall be a
16” x 20” or equivalent (320 sq. in.) in order to insure proper
furnace performance. Failure to provide return air ducts of the
specifi ed size will void your warranty.
A fi lter should be installed in the cold air return. Furnace fi lters
should be checked and cleaned/replaced regularly.
If return air is not provided, the warm air distributed into your
home will be restricted and the effi
ciency of the furnace is de-
creased. Without a return air system, warm air will be drawn
into your basement, unnecessarily heating unused areas of the
home. In extreme cases, if your basement or utility room is fairly
airtight, the blowers on the furnace could depressurize the room
and pull toxic fl ue gases from the furnace, a gas water heater, or
gas furnace. Th
e fumes could then be distributed throughout the
house.
COMBUSTION AIR
All fi res need air (specifi cally oxygen) to burn. Furnaces, fi re-
places, and wood burning furnaces need enough oxygen for
complete combustion of their fuels. Th
e incomplete combustion
that takes place when a furnace is “air starved” causes carbon
monoxide (CO) to be formed in quantities that can be danger-
ous inside a well sealed house. Having a source of combustion
air from outside the home into the room where the furnace is
installed will prevent “air starvation” of the furnace. A simple
positive air supply can be constructed using dryer vent and a
modifi ed termination.
PLENUM OPENING SIZE
Rectangular
13”[33cm] x 18”[46cm]
1” [2.5cm]
9 ft [274cm]
9 ft [274cm]
1” [2.5cm]
2” [5cm]
