Regulating the humidity levels in your home is not always an easy task. Therefore, people choose to have a humidistat installed. A humidistat is a measurement device that monitors and maintains the levels of humidity in the air. These devices are quite common, and you normally find them on portable humidifiers or integrated cleaner/humidifier units where they help to regulate humidity levels within your home.

How Does a Humidistat Work?

A humidistat comes with a sensing element that is comprised of a flat plate onto which two metal conductors are fitted. A relay amplifier is connected to the sensing element, and it captures the signals transmitted by the sensing element providing highly accurate humidity level readings.   

Using these readings, the humidistat will switch on the humidifier in case the electrical resistance indicates that the air is excessively dry. It then switches off the humidifier once the required humidity levels have been attained.

A dehumidifier or a portable humidifier is usually fitted with a humidistat to help prevent the over humidification or over dehumidification of a room. While it can effectively monitor and maintain the moisture levels of the air close to the device, it does not measure the moisture levels in other parts of your home. 

This is why having a hygrometer can be very beneficial; however, hygrometers do not regulate moisture levels as humidistats do. Based on the readings obtained from the hygrometer, you can adjust the humidity levels in the room, thereby attaining the desired humidity level.

Whole- House Humidistats

When it comes to whole-house humidistats, humidifiers or dehumidifiers are connected with the central HVAC system. In this kind of system, the humidistat is also the component that adjusts the valves, dampeners, or other HVAC system switches, thus regulating the moisture levels as well as the airflow within a home.

You can connect a humidistat to your thermostat to run the air conditioner to maintain the levels of moisture within your home separately from the temperature. When the moisture levels are low, but the temperature is high, the humidistat will not let the AC turn on. After the indoor humidity levels have reached an unfavorable humidity level, the humidistat will continue to run the AC until the humidity level lowers.

This way, you will be able to maintain favorable moisture levels within your home when away without having to run the HVAC unit more than needed.

The Problem with the Humidistat

Humidistats are designed to maintain optimal moisture levels within your home by running the HVAC system only when needed, which helps to save on utility bills. But the fact is that humidistats are not always accurate to the exact dial setting. In reality, a humidistat is often off by as much as 10 or 20%.

The main issue with inaccurate moisture level readings in colder climates is that you will end up putting warm moisture into your indoor air, and with it being cold outdoors, it will lead to the formation of condensation on the exterior windows and walls.   

Having moisture in these areas can lead to the growth of mold and mildew and not to mention a shorter lifespan of building materials and windows. 

On the other hand, the main issue with false humidistat moisture level readings in warm climates comes about when it is set to maintain a 60% humidity level and failing to allow the HVAC system to turn on until it senses 60% humidity. Keep in mind that the unit is often off by as much as 20%, which translates to 80% moisture level.

In hotter climates, this can be compared to switching off the AC and keeping the windows shut in the middle of summer. Besides that, the temperature can rise to 95 degrees, and the AC will still not turn on until the specified setting has been attained by the humidistat. 

Considering that mold normally thrives in moisture levels under 30% and over 60%, when you use a thermostat, especially in tropical and humid climates, you can quickly find yourself facing a mold problem.

Bottom Line: Do You Need a Humidistat or Not?

While it is quite clear to see that humidistats are highly beneficial in maintaining the humidity levels in your home, they also seem to do more harm than good. This is the reason why most HVAC companies forego humidistats when installing new thermostats or systems. This is also the reason why you need to avoid having one installed.