Relative Humidity (RH)

What it is: Relative humidity can affect the comfort of the room and high humidity can promote the growth of mold. The EPA recommends that indoor relative humidity be kept below 60% (ideally between 30 and 50%) to prevent mold growth and discurage pests. (Source: EPA Mold Course - Humidity)

Sources in Schools: Any source of excess water in a school can contribute to higher humidity levels. (Source EPA Indoor Air Quality Action Kit)

Health Effects: If humidity contributes to the growth of mold, asthma and allergy reactions may occur.

Devices and Measures

Room Temperature Devices

Relative humidity can be measured with many common room temperature devices or indoor air quality monitors.

Relative Humidity Measures

The relative humidity is the ratio of the current moisture capacity to the total capacity of the air to hold moisture often represented as a percent. For example, if a cubic meter sample of air at a specific temperature can hold 100mL of moisture, and it is currently holding 60ml of moisture, then the relative humidity would be represented as 60%. There is also a relationship between relative humidity and temperature. The same amount of water vapor in the air can have a different relative humidity at different temperatures because warmer air can hold more moisture.

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