Controlling the Humidity Inside During the Winter

In the winter, moisture is generated by your activities: taking showers, washing clothes, doing dishes; even watering your plants and pets puts a certain amount of humidity in your home’s air, which can lead to higher humidity levels than normal. High humidity levels within your home can cause moisture to condense on windows, water stains to show on walls, and rust, mold or rotting wood to occur within your house. High moisture levels will inevitably promote fungal growth.

In the winter, it is possible to have too little moisture in the house. Because the cold outside winter air is so dry, it affects the indoor relative humidity when it enters your home. During the heating season and well into the dead of winter when the outside air temperature drops below 15 degrees, the relative humidity inside your home should never exceed 30 percent. And in very cold weather, the humidity will need to fall below 30 percent to prevent condensation or frost developing on your windows.

These guidelines for the minimum recommended humidity levels for your home are based on a 70º F interior room temperature, as follows:

  Outside Temperature Inside Humidity
  20° to 40° F Not over 40%
  10° to 20° F Not over 35%
  0° to 10° F Not over 30%
  -10° to 0° F Not over 25%
  -20° to -10° F Not over 20%
  -20° F or below Not over 15%

These guidelines do not guarantee that condensation will not appear on mirrors, windows, toilets and porcelain sinks and tubs. Factors such as closed blinds or drapes may require you to decrease the relative humidity in your house below these guidelines. A good rule of thumb for controlling relative humidity in the winter: if frost or condensation forms on your windows, the humidity is too high. If you have hardwood floors and you notice them start to separate, the humidity is too low and you should correct the settings on your humidifier. You may need to regularly adjust a humidifier’s setting to properly control the humidity in your house.

Typically you should not need to use a humidifier in the winter because of the amount of moisture that is generated during your family’s normal daily activities unless you find that the humidity is too low, then you may need to resort to using your humidifier.

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