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D Installation In An Attic With An Existing Forced Air Hvac System; E Installation In A Structure With - Honeywell DH90 Installation Manual

Whole house dehumidifier with fresh air ventilation
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DH90 Dehumidifier • For HVAC Installer Only
Fresh air intake
Indoor air
Indoor air
Figure 3: Attic Installation.
Instead of installing a separate return to the DH90,
and if the existing system has multiple returns,
it is possible to select one to disconnect from
the existing forced air system and use it for the
dedicated DH90 return. Always select a return from
a central location in the structure in an area that is
always open to the rest of the structure. Do not use
a return from a room that may have its door closed
much of the time.
4.4D Installation in an Attic with an Existing
Forced Air HVAC System
ImPORTANT: ALWAYS install a catch pan
with a drain or float interrupt for condensate
under the DH90 in an attic or condensate
may damage the living space below.
The interrupt switch should be installed in series
with the field wire that connects the blue lead
from the DH90 to the dehumidistat. If overflow
occurs, this switch opens the compressor control
circuit and stops water production before the
catch pan overflows. The DH90 will continue to
ventilate or circulate air as normal, but will not
dehumidify until this switch closes.

Heating & A/C unit
The preferred method of installation is to create a
Attic installation
separate return for the DH90 in a central area of
the structure. Duct the supply of the DH90 to the
air supply of the existing HVAC system. Connect
an insulated duct from outside to the 6" collar of
the DH90 if you wish to provide fresh air. Adjust a
damper in the duct to provide the desired amount
of fresh air. See Figure 3.
4.4E Installation in a Structure with No Existing
Forced Air HVAC System
When installing the DH90 in a structure that does
not have a forced air HVAC system, a single return
for the DH90 should be installed in central open
area of the structure.
DO NOT locate the return in a bathroom or a
kitchen. The supplies of the DH90 should be
located in the remote areas of the structure (such
as bedrooms, den, etc.). By ducting this way, the
air inside the structure will circulate through the
DH90 to be filtered and dehumidified.
6" diameter duct is recommended for branches to
the bedrooms, 8" diameter duct is recommended
for branches to larger areas. Connect an insulated
duct from outside to the 6" collar of the DH90 if
you wish to provide ventilation. See Figure 4.
Supply air
Indoor air


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Dh90a1007 - whole house dehumidifier