How Does a Humidistat Work

Ashwini Kulkarni Sule Nov 6, 2018
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A humidistat is a small device responsible for making your winter comfortable. Read ahead to learn more about it.
Chilly winds and extreme dryness in the air make winter rough. Less amount of water vapor in the air makes it uncomfortable to stay even in the warm areas of your home or office. A good solution to this problem would be to install a humidifier to add the required amount of water vapor in the air.
However, it is necessary to control the amount of water vapor that is added to the air. This is where the role of a humidistat comes into play. This little device allows you to control the amount of humidity added by the humidifier.

The Working

The humidistat comprises a series of metallic conductors made from sensitive element which are capable of sensing even the slightest variations in the humidity. These conductors are connected to a relay amplifier. The humidity variations cause a resistance to flow through the metallic conductors. This resistance is then measured with a relay amplifier.
A humidistat either works as a standalone device to control the humidifier or is often used in collaboration with the central heating or air conditioning system. In the second case, it works in conjunction with a thermostat.
It controls the ON/OFF cycle of the air conditioner by sensing the humidity in the air. You may find the humidistat controls located next to the thermostat on the main floor or separately in the duct.
Excessive dampness is taken out from a room through the humidifier fan or vents. A desired amount of humidity can be maintained by adjusting the humidistat according to the external climatic conditions.


The humidistat's setting is dependent upon the some factors:
  • Number and type of occupants inside the home.
  • External air temperature.
  • Type of insulation in the house.
  • Vapor barriers.
  • Efficacy of weather stripping.
  • Type of windows and doors (including frames and jams).
  • Storm windows and doors
Considering all these variables, it is difficult to predict the ideal setting that will function for every household.
Humidistat should be set to 65% if outdoor temperature exceeds 20 ºF. If the thermostat and humidifier are working together, you might want to set the temperature of the thermostat too. When they work together, thermostat controls the working of air conditioner by sensing the heat in the room and the humidifier controls it according to level of humidity.
Thus, if there is more humidity in the air than heat, the working of the air conditioner will be triggered by a humidifier. In conditions with normal temperature, you should set your humidistat at 75% and thermostat at 80 ºF.
Setting of the humidistat should be appropriate, as a very low level setting may lead to excessive dryness, whereas an extreme high level can cause indoor precipitation.
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