Humidistat Guide: What It Is And Why You Need One

Last Updated May 27, 2021 By Bella Zinti

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The humidity level in your home and indoor space impacts you more than you might realize. Air that is either too dry or too humid can exacerbate skin issues and respiratory problems. Dehydration and headaches can happen when the air is so dry that your skin loses moisture or so humid that you sweat copiously. Thankfully, with a humidistat, you can easily check the moisture level of your home or indoor space and make adjustments. 

What Is A Humidistat?

Humidistat is typically included with portable humidifiers or dehumidifiers or combined air cleaner/humidifier units to control your home's humidity level or any indoor space. While devices that solely monitor humidity levels (known as hygrometer) are sometimes lumped in with humidistat, actual humidistat works similarly as a thermostat. They monitor and use that information either humidity or dehumidify the space automatically to reach levels that you can set for your home or any indoor space. 

How Does A Humidistat Work?

Humidistat is an electrical device in which two metal conductors serve as a sensing element. Humidity levels are measured by the amount of electrical resistance between these two conductors. A relay amplifier is attached to the sensing element that reads this resistance and turns the humidifier/dehumidifier to add or remove moisture level as needed to control the humidity level inside your home.

In a whole-house system, the humidifier/dehumidifier will be connected to your central HVAC system. The humidistats will then control all of the dampers and valves required in the HVAC system to control airflow and humidity throughout the house. 

How to use a humidistat

You can wire a humidistat into your thermostat so that you can use your existing air conditioner unit to regulate the interior humidity level independent of the temperature. This way, the humidistat won't let the air conditioner turn on based on temperature levels but on the humidity level. Once the interior humidity level reaches the level you set, the air conditioner will turn off regardless of the temperature. This can be helpful to maintain your desired humidity level while you're away without running your entire HVAC system unnecessarily.

Why do you need A Humidistat for your home?

Air in your home can be either too humid or too dry can cause problems both to you and your house. 

If the air in your home is too humid, it will feel muggy, clammy, and hot. You'll turn on your air conditioner to cool off, but what you need to do is dehumidify your air. Bacteria, viruses, fungus, mold, and mildew thrive in high humidity levels. This is a huge concern for anyone with allergies or asthma. It can also create condensation around windows, which will rot the sills. Paint and wallpaper can peel, wood floors can buckle, and furniture can grow mildew.

On the other hand, if the air in your home is too dry, you'll run into a different set of problems. Particularly in the winter, when air is naturally drier, you'll also run the furnace and further pull moisture out of the air. This excessive dryness can cause any wood in your house - floors, door and window frames, and furniture - to splinter and crack. It can also aggravate asthma and allergies, albeit in a different way than high humidity levels would. Chronic skin issues also flare up in dry air.

In a financial sense, having a humidistat will save you money—much of what we perceive as the temperature is related to humidity levels. Rather than running your HVAC system constantly in the summer and paying large energy bills, you can use the humidistat to control humidity levels and thereby make the air more comfortable at a much lower cost.

What Is The Ideal Humidity Level For Your Home

The ideal humidity level is between 45 and 60 percent. Many humidistat users set their levels at 55 percent to account for a 10 percent inaccuracy. You can purchase separate hygrometers to set about the house to manually monitor humidity levels further away from the humidifier or HVAC vents. If you are using your humidistats in conjunction with a whole-house system or wiring it to your HVAC, it would be helpful to talk with an HVAC professional to make sure that you don't create any moisture-related issues.

The Problem with the Humidistat

Humidistats are often inaccurate by as much as 10 to 20 percent. Particularly in portable humidifiers and dehumidifiers, the humidistat is typically attached to the appliance itself. This means that it will measure and adjust the humidity levels in the surrounding space, but the humidity levels may be very different on the other end of a large room. Even on HVAC systems, humidistats are pretty inaccurate. 

Other than a slight annoyance, does this pose any real problems? It can, predominantly with having too much moisture in the air.

In cool climates, it will typically be warm moisture that is put into the air by the humidifier. Too much warm moisture in the air of a building with a cool exterior will lead to condensation on the exterior walls and windows. This will lead to mold and mildew growth, significantly shortening the lifespan of those building materials.

Humidistat inaccuracies cause problems in warm climates where the air is already hot and humid. If you have your humidistat connected to your HVAC system, you'll save money by not allowing the HVAC system to kick on until the humidity level gets too high. However, if you set your humidistat to 60 percent humidity, but then it's inaccurate up to 20 percent, that means your HVAC system won't turn on and move the air in your home until it's reaching humidity levels of 80 percent. 

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About the author

Bella has a Bachelors degree in interior design, is a master gardener. She designs nourishing outdoor & indoor spaces guided by the practice of Feng Shui.