Good Relative Humidity for a House

Relative Humidity Basics

• Relative humidity should not be confused with absolute humidity, which is the general amount of moisture in the air with no regard to temperature. Relative humidity refers to the ratio of moisture in the air compared with how much it can hold, as warmer air can hold more water. For example, if the relative humidity outside on a 30 degree F day is 60 percent, that level will drop to 15 percent when it enters a home and is warmed to 70 degrees F, meaning that the air inside will be considerably drier. The relative humidity in your home will be higher during the summer months, as the hot air holds considerably more water vapor than cool air.

Optimal Humidity

• The Environmental Protection Agency recommends that the average relative humidity of a home be between 30 percent and 50 percent. This range will help avoid the problems associated with having air that is too dry or too moist. Relative humidity will vary according to location within a house. Basements, for example, that have little ventilation are prone to high relative humidity rates. The relative humidity may be measured with a hygrometer, which measures the moisture in the air. These may be purchased at various hardware stores.

Relative Humidity Problems

• There are a myriad of potential issues associated with having a relative humidity outside of the appropriate range. High relative humidity promotes the growth of bacteria and mold and allows for the propagation of dust mites, which cause allergic reactions in humans. Cosmetic and structural issues may occur in humid environments, as well, such as peeling wallpaper, water stains on your walls or ceilings and a musty odor. Air that is too dry, meaning that it falls below 30 percent relative humidity, causes dried-up mucus membranes and nosebleeds. This is typically only a problem in the winter months, however, because the cool air outside contains such little moisture and thus even less when it is warmed in your home.

Controlling Humidity

• There are numerous techniques and devices used for controlling the indoor relative humidity. Humidifiers use varying mechanisms to moisturize the air in dry environments while dehumidifiers suck water vapor from the air in moist environments. Use exhaust fans like those found in your bathroom or kitchen as often as possible during the summer months to suck out moist air. Close your windows during the summer, and use the air conditioner instead. The warm air outside contains a lot of moisture that will collect on your walls when it enters unless it is filtered by an air conditioner first.