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Big Joe- A humidistat and a thermostat have one thing in common-they are either on or off. You can use either to accomplish just about the same thing. I do servicework in printing plants that use thermostats and humidistats wired in series: temperature is not the first thing in mind- it's humidity that they are concerned about ('cause of the paper).
However, these types of systems have been designed to reduce compressor capacity as the overall load changes, with staging, unloaders, and also with reheats for humidity control. Some of the residential systems installed now do have frequency drive motors designed to offer optimal humidity removal by ramping the blower speeds up or down in conjunction with multi stage compressors, but a standard system isn't designed as such. If humidity is an issue even when you are satisfied at the thermostat, sizing of the system is the problem-either actual tonnage or the sizing/layout of the ductwork.


  • Rodney Summers
    Rodney Summers Member Posts: 748
    Adding a humidistat

    Wondering how to add a humidistat to my a/c split-system. Currently a 3 speed trane air handler, but I do not know how to adjust the speed. Can I add a humidistat (any brands recommended?) and possibly wire it into an existing system to control speed setting? Or maybe I can control the speed setting remotely with a switch near my thermostat?

    Anybody tied this before?
  • Jeff Lawrence_24
    Jeff Lawrence_24 Member Posts: 593
    The best way

    Is to find someone that does it for a living and pay them to answer your questions. I personally wouldn't feel comfortable giving help to someone that may not be qualified to work on the equipment.

    You will be working with electricity and sometimes that's not very forgiving....

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Design Fan Speed

    When systems are designed, the fan motor speed, the amount of airflow the system will produce, the static pressure in the duct system that must be overcome, as well as a miriad of other factors are taken into account.

    Randomly changing the speed of the blower motor can result in a number of problems that include, but are definitely not limited to, liquid floodback to the compresor, water damage to the structure and insufficient cooling.

    As Jeff mentioned, please call in a professional to evaluate your system and determine what the proper motor speed is for your system.

    THe humidistat is a device that opens and closes an electrical set of contacts depending onthe humidity level in the space and should, for the most part, not be used to control the fan speed of a system.
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