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DUCTING
INSTALLING DUCT COLLARS
The Aprilaire
®
Dehumidifier is supplied with two, 8” round collars for connecting to the inlet and outlet of the dehumidifier.
They are packaged inside the unit behind the filter access panel and must be removed. To install a collar, center it over the opening
and allow the foam seal to uniformly contact the dehumidifier. Secure with 4 galvanized sheet metal screws (not included).
Note: Use the collars supplied with the dehumidifier. Do not install reducers or restrict the inlet or outlet of the dehumidifier;
this may cause problems with the operation of the dehumidifier.
DUCTWORK
UL approved 8” diameter, insulated, flexible duct is recommended for connecting to the dehumidifier. The flexible duct should be
capable of handling at least 0.75” of negative and 2” of positive static pressure. Additionally, the flexible duct should meet and be
installed to meet all local codes and requirements for ductwork.
The duct should be installed in general accordance with SMACNA HVAC Duct Construction Standard-Metal & Flexible Duct,
“Seal Class A” regardless of the operating pressures. The operation of the dehumidifier is controlled based on the conditions of the
inlet air to the dehumidifier. Therefore, leakage at the inlet collar is particularly important to eliminate.
All joints and seams must be sealed.
The “Maximum Total Equivalent Length” of 8” flexible duct that can be connected to the Aprilaire
®
Dehumidifier is a function of the
pressures in the HVAC system. The following table can be used as a guideline for determining this.
Example:
A system with 0.5” w.c. static ∆P and (4) 90° elbows would
be able to use a maximum of 130 feet of flex duct.
Notes:
1. The dehumidifier system's air leakage is considered
to be Zero.
2. The Equivalent Length (E.L.) for one 90° elbow is 5 feet.
3. The E.L. is based on a “Minimum Allowable Airflow”
of 175 CFM with a dirty air filter and 210 CFM with a
clean air filter.
4. Equivalent duct includes both the dehumidifier inlet
and outlet ducts.
5. If the difference between “HVAC Supply Static Pressure”
and the “HVAC Return Static Pressure” exceeds 0.80” w.c.,
the dehumidifier should not be installed.
Plenum Maximum Total Total
Static Amount of Flex Flex Duct Number 90°
∆P Duct in E.L. Length Elbows
“w.c. ft ft #
230 2
≤ 0.4 240
220 4
210 6
200 8
140 2
0.50 150
130 4
120 6
110 8
50 2
0.60 60
40 4
30 6
20 8
Maximum Amount of Flex Duct in Equivalent
Length (E.L.) in Dehumidifier System at Listed
Plenum Static Pressure Drop (∆P)