Q:

What causes an increase in indoor relative humidity?

A:

Quick Answer

Relative humidity inside the home increases as the actual temperature comes closer to the dew point temperature. The dew point temperature is the temperature at which the air cannot hold all the moisture in it and some of it condenses into liquid.

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Full Answer

The relative humidity in a home increases when the actual temperature is lowered, because the dew point temperature remains the same. For example, if it is very hot outside, perhaps 100 degrees Fahrenheit, and the dew point temperature is 50 degrees Fahrenheit, and if the air inside the room is cooled to a comfortable 72 degrees Fahrenheit, the relative humidity inside the home increases in comparison to the air outside, because the actual temperature comes closer to the dew point temperature, which remains constant. Such high relative humidity could cause problems in the home, such as mold, and can be addressed by using dehumidifiers.

As the term indicates, relative humidity is a relative measure of how humid the air feels at any specific moment, depending on the relationship between the actual and dew point temperatures. The dew point temperature is absolute because it is a measure of the amount of moisture in the air regardless of the temperature.

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