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What Is a Humidistat?

Humidity and Temperature Indicator on Shelf

Humidity and Temperature Indicator on Shelf

T oday we can easily adjust all the factors that affect our home comfort. If it is too hot, the AC will be called to provide cool waves of air, and if it is too cold, we will immediately turn on the heating installation. Abnormal humidity levels can be handled either with the help of a humidifier, which can cast away the effects of low RH, or, on the contrary, by powering on a dehumidifier, which is the best solution against mold and bacteria growth. Air purification systems are available for cleaner air, and a whole range of other appliances will help you get everything straight and create a cozy environment for your family.

But what if you don’t get it right? A temperature that is either too high or too low will feel immediately. On the other hand, humidity is trickier to control, and can have more severe effects on your health and even on your house. Here’s where a humidistat will prove useful. So, stay with us as we explain how it works and how it can improve your life.

Digital Humidistat on Shelf

Digital Humidistat on Shelf

What Is The Purpose of a Humidistat?

This device is usually found in systems that deal with humidification or moisture removal and has the purpose of measuring the level of relative humidity. It can be found in hybrid units as well. For example, if an air purifier comes with a humidification function it is likely for it to incorporate a humidistat. This measuring instrument can appear in heating or air cooling installations and either increase or reduce their activity according to the values it registers.

Why Is the Control of Humidity in the Air Important?

Many factors can lead to abnormal levels of humidity, and solving the main cause, if possible, should be the first step to creating the premises for a comfortable life, especially as RH can affect you at so many levels:


If the air lacks moisture, it affects first your skin, which becomes itchy and dry. And this doesn’t happen only with the skin on your hands or face but the sensation will appear in your nose as well. This is because the membrane here lacks moisture as well. Dry cilia mean less defense against airborne particles and bacteria, and this may cause you to catch a cold faster or develop allergy-like symptoms. Furthermore, if the skin develops little cracks, they are the perfect ways for infections to settle in.

On the other hand, high humidity can be just as dangerous. Too much moisture can lead to the emergence of mold, which, can also cause allergies or, in some cases, release toxins. Too much moisture will favor bacteria growth as well, which will find their way into your system if proper air purification isn’t provided.

Furniture and Appliances

Low humidity can cause your wooden furniture or flooring to crack and peel, which can turn into permanent damage. It will also produce static electricity, which can affect your electric and electronic devices.

Too much moisture will soak your carpets and fabrics and fill them with mold, while your appliances will probably develop rust and corrosion over time, or get invaded by mold.

If you are looking to provide proper humidification for the entire home, check out our best whole-house humidifiers. Most of them integrate an accurate humidistat that will save you a lot of trouble.

How Does a Humidistat Work?

It implies the existence of a sensor made of a material that is sensitive to moisture. This element sends the signals to a rely amplifier, which reads them by measuring the electrical resistance variations according to humidity changes. These readings are further used by the device to adjust its operating mode. For example, in a humidifier, if the RH is too high, the thermostat will power the unit off. When the measurements show a value that is lower than the one you have set, the device will turn on and start releasing vapors or mist into the air.

If the thermostat is correlated with a HAVC system, it will affect its functioning according to humidity variation and not temperature. Consider the following example: Even if the optimal temperature has been reached, an air conditioning unit will continue to run if the humidity is too high to help remove the moisture from the air.

Do You Need One?

Small appliances that deal with moisture can very well function without one. They cannot affect the level of RH in such an important way to cause serious health issues or damage to the house. However, when dealing with a large system, like a furnace humidifier or a HAVC unit, it is preferable if it came with one. Automatic functions are common in this case, and they rely on sensors to create a healthy and pleasant environment.

An indoor hygrometer is a good alternative or can function as a complementary measuring device. For a humidifier is common to gather more humidity around it, so the values shown by the humidistat may be a bit off. By placing a hygrometer on the other side of the room, you can obtain more accurate data.

What Are the Benefits?

  • It prevents under- and over humidification
  • Can be paired with both cooling and heating system
  • Automatically adjusts running time so you don’t have to do it
  • Reduces electricity costs
Pointing the Ideal Indoor Humidity Level

Pointing the Ideal Indoor Humidity Level

What Should Your Humidistat Be Set At?

The optimal RH level in a home should be between 30% and 60%, so your device should focus on keeping the values between this interval. Thus, it is recommended to set it between 35% and 45%, especially in the summer, when humidity tends to increase.
If you are going on vacation, you can set your appliances to work more economically. Studies have shown that mold grows when the humidity has reached a value of 78%, so you will want to keep air moisture below this limit, but not as low as you would keep it if you were at home, since in this period it cannot affect your health.

How Accurate Are these Devices?

Unfortunately, it is rather difficult to find a device that can provide precise RH readings. In many cases, the readings ore off with 5%, 10%, or even 20%, and this can easily turn into a huge problem. If the device is connected to your heating system, it will power it off even if the desired temperature hasn’t been reached if it senses that the air is becoming too dry. But if the measurements are not accurate and the air is still damp, this can lead in time to mold problems. The same goes for the air cooling systems, so it can basically ruin your home comfort and create the conditions for health issues.

Will a Humidistat Help You Save Money?

The short answer is yes, and you have probably figured out by now that by not keeping your appliances working 24/7 but only when more or less air moisture is required, you will reduce energy costs. However, there are some financial benefits you have probably not thought about, as this device won’t only save energy but reduce repair expenses:

  • It can increase your exhaust fan’s lifespan – By not running it all the time, it reduces wear and increases the distance between repairs.
  • It reduces electrical hazards – Wires don’t mix well with moisture, as it causes rust and can lead to electrical shorts. If the wires are in the walls, the repairs will be considerable. Not to mention that damaged wires can cause fires and completely ruin your home.
  • It keeps the house in good shape – If mold starts taking over the walls and the objects inside, it will cost you good money to restore them. From cleaning solutions, and maybe professional cleaning, to complete replacement of some items, the expenses can easily go over the roof. By keeping humidity under control, it prevents the emergence of these problems.
  • It keeps your appliances working for longer – Mold and rust can invade coils and pipes, increasing the repair costs.

The Bottom Line

A good humidistat can in time increase or preserve the value of your home. If moisture is kept under control, degradation cannot settle in, and the walls, floors, ceilings, wiring, along with all the objects inside will last longer. Plus, you will never have to deal with musty odors that are released by mold or spend extra on HEPA purification technologies to avoid inhaling the spores. Your health will gain a lot and your comfort will be improved. So, if you are still wondering if you should invest in one, the answer is yes. Just do your research and buy a reliable model that can provide you with accurate measurements.

Lillian Davies
Lillian Davies
Lillian is a fresh college graduate who has lived in Tucson for most of her life, battling the torrid heat ever since she was a child. She is quite versed in the topic of thermal comfort and what solutions work to make conditions more bearable when the temperatures go haywire, which makes her knowledgeable in the topics she writes about here. Since she is a perfectionist, Lilian always takes time to polish her articles before release, which makes her an irreplaceable part of the team.
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