You Have a Thermostat, But Do You Need a Hygrometer, Too?

By: Cherise Threewitt  | 

Hygrometer
Hygrometers measure the amount of humidity in the air. This one, which is showing very high humidity, has a thermometer. Photo by Alex Tihonov/Getty Images

Air has water vapor — or humidity — we are sensitive to, our skin especially. We sweat to stay cool, but when the air's relative humidity is super high, our sweat won't evaporate. You know that sticky feeling when you're saturated with sweat. As a result, it feels much hotter than it actually is when humidity is high.

The reverse is true when humidity in the air is low; our sweat evaporates easily, which cools us off. But how do you know what the humidity level is? You can use a hygrometer to find out.

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Hygrometers are tools used to determine the level of water vapor in the air. Many also measure temperature because it's an important factor in determining humidity.

Hygrometers first became available in the 15th century in varying designs. Leonardo da Vinci was an early developer of the tool; his design measured the difference between absorbent and nonabsorbent materials. This difference was caused by moisture absorption from the surrounding air and could be used to calculate relative humidity. Another early design was by Swiss physicist and geologist Horace Bénédict de Saussure in 1783. It measured the atmosphere's effect on the tension of a strand of hair in the device to figure out humidity in the surrounding air.

Today, there are several different types of hygrometers. Like many scientific tools, there are affordable versions for casual purposes, and their accuracy and prices increase exponentially for professional-grade versions used by meteorologists. Their uses vary as much as the prices and include:

  • weather forecasting
  • construction and industrial production
  • moisture control in a home
  • plant care in greenhouses
  • regulating humidity in residential and commercial saunas
  • sensitive materials storage (art, artifacts, papers, musical instruments) at museums or other archives buildings

There are different types of hygrometers, too.

  • mechanical: Measures the expansion and contraction of organic materials.
  • electrical: Measures the change in electrical resistance of a conductive material. They are available in two main types, resistive or capacitive. The former measures the contraction of ceramic caused by humidity, and the latter measures electricity passed through two metal plates, which are affected by humidity.
  • dew point: The most precise type, which measures actual condensation on a cooled piece of metal.
  • psychrometer: Measures the difference in temperature between two thermometers, a dry thermometer and a wet thermometer.

Hygrometers can also be useful for personal health because air that's too dry can be uncomfortable and air with too much humidity can enable mold and pathogens to thrive. Inexpensive hygrometers can be used to monitor the humidity of a home, office or workspace for these purposes.

If your home has creaky wooden furniture, lots of dust and static electricity — especially when you touch a door handle or light switches — you probably have low humidity. If your home's humidity is too high, you might have mold or wet windowsills from too much condensation.

To determine your home's humidity, simply place your hygrometer in a living area away from the kitchen and bathrooms. According to ThermoPro, a manufacturer of hygrometers, humidity in the home should be kept between 40 and 50 percent. If the humidity is too low, consider adding a few room humidifiers or a whole house humidifier that is installed as part of your home's HVAC system. Dehumidifiers can help you control the opposite problem.

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