Aprilaire 4655
Aprilaire Manual Humidistat spst Wall or Duct Mount
Price:$30.00
  Manual Automatic Automatic Automatic

Aprilaire 4655 manual humidifier control is designed for low voltage (24v) control of humidifiers in central heating and air conditioning systems. This humidistat can be wall or duct mounted. Includes humidistat, as shown in our photos.

Body measures: 6 x 3-3/8 x 1½ inches.
Color: White

An increase in relative humidity (RH) expands the nylon ribbon which opens the control switch (spst) to stop operation of the humidifier. A decrease in RH reverses the process and closes the control switch.

This is a MANUAL humidistat, which refers to having to adjust the humidistat based on outside temperature. See below.

Manual Versus Automatic Humidistat

The indoor humidity level needs to be set based on the outside temperature. This is to prevent water from running down the windows. The cool air near the windows can not hold the humidity and water will condense on the glass. To prevent this condensation, the indoor humidity level is sacrificed by lowering the humidistat.

An automatic humidistat (Aprilaire 60) adjusts the humidity by using an outside temperature sensor.

The Aprilaire manual humidistat as used in earlier Aprilaire humidifiers (Model 4655) requires adjusting the relative humidity based on the outside temperature. A manual humidistat needs to be set back as the season gets colder. The chart below shows the humidity setting for a range of outside temperatures.

When The Outdoor
Temperature is
This Relative Humidity
Should Be Maintained
+40°F
45%
+30°
40%
+20°
35%
+10°
30%
25%
-10°
20%
-20°
15%

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