Guitarists, greenhouse operators and cigar aficionados need to know humidity levels to protect instruments, plants and valuable smokes. But most likely you want to measure humidity in your home, particularly the basement, to make it less damp and more liveable, and to avoid mold and dust mites. Conversely, you don't want your house to be too dry, which can make your home feel colder during the winter heating season.
A number of devices, such as a combined thermometer with a humidity dial, allow you to get an approximate reading for as little as $3, while fancier meters -- technically called hygrometers -- can provide more accuracy. Simple readouts tell whether your conditioned spaces are in the preferred range of 30 percent to 50 percent relative humidity.
Absolute humidity measures the amount of moisture in the air, while relative humidity also factors in temperature, to give an idea of how saturated the air is compared to its ability to retain moisture at a given level of heat or cold. Relative humidity is the more important measure for goals such as personal comfort and mold control.
While you can in theory make your own hygrometer by swinging around a pair of thermometers, with one having its bulb wrapped in a wet cloth, you'll find it more convenient to set up a commercial device for constant measuring.
This simple, affordable device shows the relative humidity to plus or minus 10 percent. They may be sufficient if you simply want to track basement humidity in the spring and fall, to see when you need to turn on and turn off your basement dehumidifier as the seasons change. Wait an hour after you first set one in place, or after abrupt changes in humidity, to get the best reading.
A digital hygrometer costs more but gives greater accuracy, closer to plus or minus 2.5 percent, on the continuum from 5 percent to 25 percent at the "dry" end, to 95 percent to 98 percent at the "wet" end of the spectrum, and temperature readings from 32 to 122 degrees Fahrenheit. You'll get a relative humidity reading by default, or by pressing an "RH" button, on an LCD screen. Some feature magnetic attachments for easy placement. Others are portable, handheld meters or the size of a pen and include a pocket clip, with built-in sensors. Models may also allow you to set an alarm if the relative humidity becomes too high or low for your preference.
These fun gizmos include a remote sensor so that you can see at a glance both indoor and outdoor temperatures and humidity. The indoor humidity readout may include a simple icon indicating "High," "Low" or "Ideal."