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What is the Ideal Indoor Humidity

Thanks to advanced thermostats and HVAC upgrades like whole-house humidifiers and dehumidifiers, homeowners now have more control than ever over the humidity level in their home. But as always, with great power comes great responsibility. Humidity levels that are too high or too low can cause damage to your home and have a negative impact on your family’s health and comfort. So if you have the power to set your home’s humidity level, what should you set it at?

Broadly, the Environmental Protection Agency (EPA) recommends that indoor humidity levels should be in the range of 30-50%. Below 30-35%, you begin to see issues associated with too-low humidity, including static electricity, nosebleeds, and cracking wood floors and furniture. On the other hand, the Centers for Disease Control (CDC) warns that indoor humidity over 50% encourages the growth of mold. In addition, the American Society of Heating, Refrigeration and Air Conditioning Engineers reports that the ideal indoor humidity for health is 45-55%. Based on these recommendations, it would seem that you’d want to keep your indoor humidity around 45-50%. However, that’s not necessarily the ideal humidity year round.

You see, when temperatures outside drop, overly high humidity levels inside your home can lead to condensation on your windows or even inside your walls. And that can lead to damage and mold growth. This is a bigger problem in very cold climates, but here in the Tennessee Valley it can still be an issue during the coldest months of winter. From December through February, we commonly see outside temperatures in the range of 20-40 degrees Fahrenheit. According to the Minnesota Department of Public Services, at those temperatures indoor humidity needs to stay below 40%. On those rare days when the outdoor temperatures fall into the 10-20 degree range, the MDPS recommends an indoor humidity of no more than 35%.

Therefore, the answer to the question “what is the ideal indoor humidity level?” is, it depends. During the warmer months, the main issue is making sure that the humidity doesn’t go over 50%. There’s not much chance your humidity will drop too low during an Alabama summer! But during the coldest months of winter, outdoor temperatures need to be taken into account along with the need to maintain comfort. Then the ideal indoor humidity will generally be around 35-40%.