* multiply by 1.1 if 208V
†
for more exact airflow use the chart included with the
blower or see Bulletin 20-040.
Attach Main Duct. Attach the plenum to the adapter
by inserting it over the supply adapter. If using sheet
metal duct, use three (3) or four (4) equally spaced
sheet metal screws or nails to secure the duct to the
supply adapter. Then tape around the seam with UL
181A aluminum tape. Then wrap the outside of the
plenum adapter with the supplied blanket insulation
and secure the insulation seams with UL 181A tape.
Return Air Duct. Unico supplies a return duct system
but any return duct system is acceptable provided the
pressure loss does not exceed 0.15 inches of water (37
Pa), including filters. The return duct should have at
least one 90° bend between the unit and filter box to
reduce sound transmission directly from the unit.
The Unico Return Duct system has a single return that
includes the return air box with filter, the return duct,
and the return air adapter (refer to Fig. 3). Multiple
returns or extra-long returns are possible so long as the
maximum pressure loss is not exceeded. For vertical
installations or tight spaces, it may be necessary to
fabricate a return duct system from duct board or lined
metal.
The typical return duct is 10-foot (3 m) in length so it
may have to be cut to avoid bunching if the distance to
the unit is significantly less than 100-inches. The
minimum length should be 7-feet (2 m). When given a
choice, the shorter distances should be avoided as this
may increase sound transmission from the unit.
Cut an opening for the return box as specified in Table
1. For the 2430, 3036 and 3642 if the joists or studs are
on 16-inch (410mm) centers, there is no need to build
a frame to hold the return air box. Otherwise, it will be
necessary to construct a frame around the opening. For
the 4860 return, it will almost always be necessary to
cut and header at least one joist.
Center the return air box so the filter frame flange
covers all the gaps and make sure the flange is flush
against the wall or ceiling. Install the return air box
against the frame using nails or screws.
Screw holes are provided in the return air box. Use the
holes nearest the corners. The other holes are for
mounting the filter grille. See Fig. 19.
Figure 19. Return Air Box and Filter
Install filter frame into the return air box using four
nails or screws. Use the holes furthest from the
corners. Insert filter and hold in place by rotating metal
clips. Close grille and secure with clips.
Refer to Table 5 for correct Return Duct Adapter
selection. Attach the proper return duct adapter to
either the Heating or Cooling Module. Then attach the
return duct to the adapter and to the return air box
using the Q-bands and Q-clips.
The return air adapter ships with an insulation blanket
that must be wrapped around the adapter. Tape the
seams with UL 181A aluminum tape.
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