The Environmental Protection Agency (EPA) lists indoor air quality among its top environmental health threats.
There are three key components to healthy air. It must be fresh, clean, and have the proper humidity (less than 50% relative humidity). Fresh outside air is rich in oxygen and flushes your home of stale air, which is full of harmful airborne pollutants.
Yet, outside air is not necessarily clean air. In order to have clean air, it must be filtered to remove particles, airborne allergens, and other biologicals.
Maintaining relative humidity below 50% prevents dust mite infestations, mold and mildew growth, and inhibits bacteria. This lower relative humidity also reduces the out-gassing of VOCs. In colder climates, wintertime humidity levels must be even lower — generally 30–40% — to prevent condensation on windows and other surfaces.
Unless you live in an arid climate, periods of high humidity create a myriad of problems for structures and people. Symptoms of high humidity would include:
Every homeowner should own a hygrometer that measures temperature and relative humidity (RH). The ideal relative humidity for health and comfort is about 40–50%. In the winter months, it may have to be lower than 40% RH to avoid condensation on the windows.