Harman® • PF-120 Installation Manual_R1 • 2014 -___ • 03/14
23
3-90-08121i
DO NOT CONNECT TO A DOwN FLOw FURNACE.
DO NOT CONNECT DUCTwORK SO THAT A REVERSE
FLOw IS POSSIBLE.
Recommendations for Supply Air and Return Air duct
sizing.
The speed or velocity of air moving through duct systems
increases as the duct decreases in size with the same CFM
blower. The sound of air flowing through the duct increases
as the velocity increases. Therefore the largest duct size
practical should be used.
The velocity to sound level must be taken into consideration
when connecting this furnace into an existing duct system.
As a primary source furnace the duct system can be installed
to fit the customers needs.
Velocity
500fpm
700fpm
900fpm
Static-In.
W.C. .3 Minimum to .6 Maximum
1638 cfm
470 in²
360 in²
290 in²
(These duct sizes are only recommendations.)
The Return Air duct system should be sized approximately
10 percent larger for heating only systems and 20 percent
larger if air conditioning is installed.
Regardless of the supply air duct size installed, the
Distribution Blower Motor
MUST
be checked for running
Amperage. Check the motor name plate for the full load
AMPS. If the amperage is running higher than that listed, a
supply air restricting damper may be required to increase
the supply plenum positive static pressure.
NOTE:
It is highly recommended that the furnace
control be turned to the “OFF” position when
air conditioning is being used, whether or not
it is interconnected.
CAUTION
!
