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USSC 11
1. For installations with horizontal through-the-wall exhaust, it is strongly recommended that the heater combustion
air be connected to the outside. If the home is newer or has been tightly insulated, it is required to install outside
combustion air.
2. Connection to outside the house is REQUIRED for mobile home installations. We strongly urge use of the 69FAK
Fresh Air Kit.
90 DEGREE BEND TERMINATION WIND HOOD TERMINATION
2” Min. Diameter
Wind Hood
2”
3”
6”
NOTE:
A wire mesh screen with a maximum
opening size of 3/8” must be
installed in the pipe or elbow for
rodent exclusion.
DESIGN GUIDELINES FOR OUTSIDE COMBUSTION AIR CONNECTION
3. Only noncombustible pipe 2 inches (or greater) in diameter is approved to use for outside air connections (straight
or exible). PVC pipe is NOT approved and should NEVER be used.
4. If the air inlet is connected to the outside, it MUST be terminated with a vertical 90-degree bend (down) or with a
wind hood. Failure to do so could result in a burn back during high winds blowing directly up the air inlet during a
simultaneous power failure (see diagram above).
5. Blockage, excessive length, or extra bends in the air intake pipe will starve the heater of combustion air. A 90-degree
bend is equivalent in restriction to approximately 30 inches of straight inlet pipe.
CAUTION: The operation of exhaust fans such as bath room fans, attic fans, etc. might starve the heater of combus-
tible air creating a negative pressure in the room. Provide adequate ventilation in the room accompanying the heater.
If not, the pressure switch may shut off operation of the heater. (Due to negative pressure)