Humidifiers and Dehumidifiers

Measuring Moisture Levels

Hygrometers and humidistats

Hygrometers and humidistats, while serving similar functions, are actually two different tools. A hygrometer measures the water-vapor content of air, letting you know the relative humidity of your home, whereas a humidistat lets you control humidity levels.

Hygrometers can be purchased in portable, hand-held units. They're a good way to check humidity levels before you buy a humidifier or to safeguard against over-humidification if you already own one.

Oddly enough, hair is a pretty good way to measure humidity. In a hair hygrometer, human or horse hair is held between two levers, expanding when humidity rises and contracting when it falls.

These measuring tools are mechanical or electronic and are often combined with thermometers. They should be placed away from direct-heat or moisture sources (stove, kitchen, bathroom) and can take up to two hours to provide an accurate reading.

Pros and cons of mechanical and electronic hygrometers:




$30 to $60

$10 to $20

Power Source


None required


Good in mid to high humidity ranges, under 30 percent can be inaccurate

Good if calibrated correctly


Plastic with LCD display

Wood or plastic, usually round with dial display and pointer


Can stick if humidity stays the same for a long period of time

Can be slow to respond to humidity


Can't be physically corrected

Can be corrected by adjusting the pointer

Humidistats are found on many newer humidifier or dehumidifier units. They measure humidity in the air and control it by starting and stopping the machine when needed. That way, you can leave the unit turned on and let it regulate itself - most of the time.

Some humidistats can't be set for relative humidity levels lower than 30 percent - a problem if the temperature outside the home is less than 20 degrees. When it's colder outside, even low humidity levels inside will cause condensation to build up, leading to mold and mildew problems. The colder it gets outdoors, the less you should be humidifying your home.

Wired humidistats can be bought with one or several plugs to accommodate humidifiers, dehumidifiers and fans that don't have gauges already built in. They control humidity by cutting power when moisture levels get too high or too low. Their biggest downfall is cost, which can be up to a few hundred dollars.

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