9
if a minimum two inch clearance is available. If
desired, the return opening can be located inside
a closet with louvered doors that have an open
area equal to or greater than the return grille.
The return air grille can be placed in the wall
of a closet and the air ducted into the fi lter box
through a boxed-in area at the closet fl oor level.
Make sure the fi lter is readily accessible.
After determining the location of the return air
opening, start the installation from under the home
by cutting a small hole in the fi ber underboard to
determine how the fl oor joist location will affect
cutting the opening needed for the box. Floor
joists generally are located on 16” centers, leav-
ing 14-3/8” between joists. After measuring the
return air box, cut the hole through the fl oor so
that the box will fi t between the fl oor joists. Care
should be taken when cutting through carpeting
to avoid snags. In most installations it will be
necessary to cut a similar hole in the fi berboard
directly under the hole in the fl oor. However, if
the fl oor is more than ten inches deep, it will only
be necessary to cut a hole for the collar on the
return air box or for the insulated duct.
Set the box into the opening and fasten with
screws or nails. Put the fi lter and return air
grille in place.
Note: For highly resistive duct systems it may be
necessary to add an additional return air duct to
achieve maximum performance.
Locating and Installing the Supply
Damper(s)
When locating the supply damper(s), carefully
check fl oor joists and frame members that could
interfere with the installation of the damper or
fl exible duct. Ideally, the damper should be
located in the bottom of the main duct, forward
of center of the home, at least three feet from
the nearest register. The round supply opening
in the slanted side of the damper should face
the side of the home where the heat pump is
located. To locate the center of the heat duct,
fi rst cut a small hole in the fi berboard below the
duct at the desired location. After locating the
duct center, cut a hole approximately 3/4” larger
than the damper opening in the fi berboard. Cut
a 9-1/8” x 13-1/8” hole in the duct and bend over
all tabs fl at on the inside of the heat duct. After
inserting the damper into the duct, bend over
all tabs fl at on the inside of the heat duct. Seal
the opening between the fi berboard and damper
or fl exible duct.
DUCTING SYSTEM
Duct Requirements
The supply duct system, including the number
and type of registers, will have much more ef-
fect on the performance the system than any
other factor. The duct must be suffi ciently large
to conduct an adequate amount of air to each
register.
THE HEAT PUMP SYSTEM WILL NOT COOL
OR HEAT THE HOME IF THE AIR IS LOST
TO THE OUTSIDE THROUGH LEAKS IN THE
DUCT SYSTEM. ALSO, DUCTS WHICH ARE
COLLAPSED OR RESTRICTED BY FOREIGN
OBJECTS WILL PREVENT ADEQUATE AIR
FLOW.
Figure 9. Supply Damper
AUTOMATIC DAMPER IS CLOSED
WHEN HEAT PUMP IS OFF
Figure 8. Return Air Box
