HVAC Air Conditioning System Dehumidistat Settings

Dehumidistats are devices typically installed with air conditioning heating and coolingsystems in Florida homes where the home is unoccupied during the summer months.  Humidistats are installed for economic reasons to reduce the run time of the air conditioning system and therefore lower utility cost.  There is much confusion as to exactly what these devices do and on how to set them.  Here, we will take the mystery out of the vacation dehumidistat and provide help in setting the control properly.
Most dehumidistats are wired in series with the power to the thermostat (although some older units are wired in parallel).  The device is nothing more than a switch which closes the circuit to the thermostat when the humidity is above the setting on the dial.  It is normal to see the display go blank on a digital thermostat when the humidity is below the dial setting.  When wired in series, it takes both a humidity level in the home above the dial setting and the temperature in the home above the thermostat setting, before the system will run.  The idea is that it can be 90 degrees in the home, but unless there is high humidity, the system does not need to run (and therefore saves electricity).  When the home is occupied, the dial should be set to ON to prevent the dehumidistat from interrupting the air conditioning operation.
On units wired in parallel, the dehumidistat acts to override the thermostat.  The system will run when the humidity is above the dial setting regardless of the temperature.  This method is not as efficient and is no longer widely used.
When leaving for extended periods during the summer months, set your vacation dehumidistat and thermostat as follows:
              DEHUMIDISTAT DIAL: 70% (Relative Humidity)
              THERMOSTAT MODE: Cooling
              TEMPERATURE: 70 Degrees
We have found these settings to be best to reduce the chance of mold/mildew growth and still provide adequate utility savings. 
If you have any questions about vacation dehumidistats or need to have one installed, please give us a call (954) 772 – 0079.

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3 Responses to “HVAC Air Conditioning System Dehumidistat Settings”

  1. x-ray technician Says:

    December 1st, 2010 at 3:17 pm

    Pretty nice post. I just stumbled upon your blog and wanted to say that I have really enjoyed browsing your blog posts. In any case I’ll be subscribing to your feed and I hope you write again soon!

  2. Herbert Boudrot Says:

    April 12th, 2012 at 5:48 pm

    I just purchased a home in jan 2012 i installed a honeywell h8908b humidistat to control the humidity did i do the wrong thing i talked to progress energy and was told this was what i needed and to set the control on 65% on the humidistat and 85% on the thermastat? do i need a dehumidistat ? thank you Herb

  3. admin Says:

    April 17th, 2012 at 9:39 am

    If you are living in the home and running the air conditioning then you should set the humidistat to “ON” and let the ac unit control the humidity. Only when you are living the home for extended periods of time say a month or longer then you turn the humidistat to 65 and the thermostat to 85 this saves your from the cooling cost while keeping the humidity under control. Sorry for the delay in the response but your comment had gone in to the spam folder.

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