What Is a Good Humidity Level in a House?

The humidity level inside your house is just as important as the temperature. High humidity makes you feel clammy and cold, even when the temperature is in a comfortable range, whereas low humidity can inflame your respiratory tract and make you more susceptible to colds and flu. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends keeping the humidity below 65 percent, while the Environmental Protection Agency advises keeping it in a range between 30 and 60 percent.

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How to Measure Humidity

You measure humidity with a hygrometer. You can buy one for less than $20 at any big box store. You should keep two things in mind when using one. First, because humidity changes with temperature, a hygrometer won't give you an accurate humidity reading if the temperature around it is constantly fluctuating. Consequently, the hygrometer should be in a part of the house in which the temperature remains fairly constant. The second thing to remember is that some hygrometers have to be calibrated before they will give accurate readings. You should find the calibration instructions -- if needed -- in the package with the hygrometer you purchase.

Signs of High and Low Humidity

You don't always need a hygrometer to determine that the humidity in your house is outside the comfort zone. You can be fairly certain the humidity is too high if you notice any of the following:

  • Mold growing on walls, ceilings, floors and baseboards. Windows are a special case -- mold may grow there because of condensation that collects due to the temperature differential at the glass, even if the room humidity is within the acceptable range.
  • Musty smells, which often indicate the presence of mold.
  • Condensation on countertops, walls and trim.
  • Peeling paint, which is often a sign of condensation
  • Frequent unexplained false alarms from your smoke detectors. Condensation from humid air can collect on the sensors and trick them into sounding an alarm.

The signs of low humidity are often felt rather than seen. Common symptoms include dry sinuses and scratchiness in the throat. In addition, your eyes may dry out quickly, causing redness and itchiness, and you may notice dry, itchy skin, which can turn into eczema or psoriasis in severe cases.

Raising and Lowering Humidity

Humidity-modifying appliances available on the the market are appropriately named for their functions: humidifiers raise humidity, while dehumidifiers lower it. These appliances are rated for a certain volume of air, which is based on room size, so be sure to select one that can handle the space in which you plan to use it.

A humidifier works by introducing a fine mist of water in the air from a reservoir that you fill periodically. If you don't have one of these appliances, you can also raise humidity by:

  • distributing bowls of water throughout the house.
  • hanging your laundry to dry inside the house.
  • boiling water on the stove.

A dehumidifier functions much like an air conditioner. It contains a set of refrigeration coils that condense moisture into droplets, which flow into a reservoir or into a drainage hose. If you have an air conditioner, turning it on is a good way to lower the humidity in the room in which it is placed, although this may not be a good option when the temperature is already low. Some other ways to lower humidity include:

  • improving air circulation by opening windows or using fans.
  • moving houseplants outside.
  • replacing the filters on your home's central air system.

Condensation from humid air can cause a number of problems, from mold and mildew to rot and even structural damage. Installing one or more ceiling fans and running them at a low speed is a good way to keep condensation under control.