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• Setting A Humidistat
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Residential Heating & Cooling

Setting A Humidistat

Generally the comfort range for  humidification is between 25 percent and 50 percent RH.  It is desirable to keep the humidity in the living space within this range as long as condensation does not occur on windows and walls.  The point condensation occurs at, is affected by the building structure and outdoor temperature.  As the outdoor temperature changes, the humidistat should be reset to keep the humidity level in the building below the condensation point.

The set point scale of the humidistat is indexed directly to the outdoor temperature for convenience.  It is recommended that the humidistat be set to the prevailing outdoor temperature.  This provides optimum humidity control for most installations.

If the proper outdoor temperature setting is used and condensation forms on the windows or walls, reduce the set point 5 F (3 C).  Frost or condensation should disappear from windows within 24 hours; if not, continue reducing the set point until it does disappear.

If the humidistat is set to the proper outdoor temperature and condensation does not occur, the humidity level in the living space may be increased if desired.  Raise the humidistat set point in 5 F (3 C) increments until condensation just begins to appear.  Then reduce the humidistat setting by 5F (3 C). 

The hygrometer indicates the ambient humidity directly in percent RH.  It provides an accurate indication of the ambient relative humidity.

Wall Mount Humidistat

The humidity set point should be set for the prevailing outdoor temperature.  This provides optimum relative humidity control for most installations.  The humidity level may be adjusted to a particular structure by using the above procedure.

Duct Mount Humidistat

If the temperature at the humidistat location on the return air duct is less than 80 F (27 C), use the procedure for all mounted humidistats shown above.

If the air surrounding the humidistat is greater than 80 F (27 C), the recommended setting should be reset to compensate for the elevated ambient temperature.  High surrounding ambient temperatures will cause the humidistat to control at an increased setting.  To determine the compensated set point for surface mounted humidistats with high ambient temperatures, use the following procedure.

1. With a bulb type thermometer, accurately determine the surrounding duct temperature at the humidistat location.
2. Decrease the recommended setting about 10 F (6 C) for each 5 F (3 C) above 80 F (27 C) at the humidistat location.  For example, the outdoor temperature is 0 F (minus 18 C), and the temperature at the humidistat is 90 F (35 C).  The compensated set point should be minus 20 F for the 10 F above ambient temperature (minus 18 C setting minus 12 C for the 8 C above ambient temperature).

Checkout

Place the system in operation and observe through at least one complete cycle to make certain that all components are functioning properly.