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What is Relative Humidity?

Posted by John on September 27th, 2008

Keep your indoor relative humidity below 50 percent to avoid growth of mold and dust mites. That’s standard advice for allergy sufferers. But what exactly is relative humidity?

Relative humidity is a measurement of the amount of water vapor in the air expressed as a percentage of how much water vapor the air could hold. If relative humidity is 100 percent, for example, then it’s raining. Most people are comfortable with an indoor relative humidity of 45 to 50 percent. When relative humidity goes above 50 percent, the excess moisture in the air makes it easier for mold and dust mites to spread.

When you control your indoor humidity, you can not only control allergy and asthma triggers, but you can also make your home’s climate more comfortable (and save money on heating and cooling bills). According to howstuffworks.com: “If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling us off. For example, if the air temperature is 75 degrees Fahrenheit (24 degrees Celsius) and the relative humidity is zero percent, the air temperature feels like 69 degrees Fahrenheit (21 C) to our bodies. If the air temperature is 75 degrees Fahrenheit (24 C) and the relative humidity is 100 percent, we feel like it’s 80 degrees (27 C) out.”

HumidifiersBased on this understanding of relative humidity, people can save money on heating bills by using humidifiers during the winter to make the air feel warmer. Humidifiers also soothe dry skin and sinuses by restoring moisture to the air.

dehumidifiersDehumidifiers, on the other hand, remove excess moisture from the air, making it difficult for mold and dust mites to thrive.

humidity gaugesYou can monitor your relative humidity using a humidity gauge, or hygrometer.

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