GeneralAire DH70 Dehumidifier - Manual (Page 3)

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B. Ducting for Dehumidification
For the ideal installation, draw air from the central part of the home and return it to the isolated areas of the home like the
bedrooms, den, utility room, or family room. The ductwork of the existing HVAC system can be used to supply air to the
home. If the existing supply duct adequately serves all areas of the home, discharge the supply air of the DH70 into the
return of the existing HVAC system where it can distributed throughout the space. The existing return duct, if adequate,
may be used as return for the DH70,
DO NOT draw air directly from the kitchen, laundry, or isolated basement. You may
draw air from a basement that is open to the home. All flexible ducting connected to the DH70 should be approved by
local codes and in most cases insulated.
• Return air ducts should be designed to allow unimpeded air flow to the return side of the system. For returns less
than 10’ in length, an 8” round or equal may be utilized. Multiple returns are acceptable.
• The supply air outlet and the return air inlet are located on each end of the DH70. A length of acoustical flex
ducting on the outlet of the DH70 will reduce air noise. A length of flexible ducting on all DH70 duct connections is
recommended to reduce noise and vibration transmitted to rigid ductwork in the structure.
• Ducting the DH70 as mentioned in the “Ducting” sections requires consideration of the following points:
• Duct Sizing: For total duct lengths up to 10’, use a minimum 8” diameter round or equivalent rectangular
For longer lengths, up to 25’, use a minimum 10” diameter or equivalent duct size. Grills or diffusers
utilized must not excessively restrict airflow.
• Isolated Areas: Effective dehumidification may require that ducting be branched to isolated, stagnant
areas. Use 8” or larger diameter branch ducting to each of two or three areas, use 6” or larger to each of
four or more areas.
Connecting to Existing HVAC Systems: For proper operation, connecting to existing air handler and duct systems
requires the fans of each system to be interlocked utilizing the low voltage interlock method provided in the DH70 low
voltage connection diagram. Refer to low voltage connection diagram in this document and on the unit.
C. Installation in a Basement or Crawl Space with an Existing Forced Air HVAC System (Whole
House Dehumidification)
If the structure in which the DH70 System is to be installed has an existing forced air HVAC system, and this system
serves the areas that are desired to be controlled, utilize the HVAC system to make the DH70 System installation easier
and provide better whole house type system performance.
Basement or Crawl Space Installation: Install a separate 8” return for the DH70 in a central area of the structure or if
the return ducting is adequate tap into the existing return duct system near the return air grill. Duct the supply of the
DH70 System to the return ducting of the existing HVAC system. The fan interlock provision must be utilized for proper
system performance.
D. Installation in an Attic with an Existing Forced Air HVAC System (Whole House
Dehumidification)
ALWAYS install a secondary drain pan with a drain or float interrupt for condensation under the DH70 in an attic to
prevent condensate overflow that may drip down damaging the ceiling or living space below.
Install a separate 8” return for the DH70 in a central area of the structure or if the return ducting is adequate tap into
the existing return duct system near the return air grill. Duct the supply of the DH70 System to the return ducting of the
existing HVAC system. The fan interlock provision must be utilized for proper system performance.
E. Installation in a Structure with Two Forced Air HVAC Systems (Whole House
Dehumidification)
Attach the DH70 return to an independent return from the upper level. Attach the DH70 supply to the return of the
basement HVAC system. This will promote circulation of air through the whole structure from the upper level to the lower
level through the DH70. If the DH70 is not connected to both HVAC systems, it may not control the humidity of the entire
structure. The fan interlock provision should be connected to the lower, ducted, HVAC system and must be utilized for
proper system performance.