How do I reduce humidity in my basement? It’s over 80% down there!

I just bought a 25-year-old house and the humidity is very high in the basement — regularly over 80%. It’s cold down there and our feet freeze when we go downstairs, even if the weather’s hot. There are small vents on each side of the basement that I open most of the time. Do we need more ventilation? I expect so, but don’t know what size. What should we do?

Humidity and Temperature Meter_hygrometer 113

The first thing to consider is what you’d like your basement to become. A dry, unfinished storage area is easier to create than a finished living space. Either way, it’s vital you understand that ventilation of a basement during hot, humid weather is the worst thing you can do. It just admits more moisture into the basement that eventually condenses because of the cool temperatures. The source of the moisture you’re battling is the air itself.

  • Your first step is to buy and use a large dehumidifier during warm weather.
  • Shut all basement vents, and run the dehumidifier until humidity levels are at least lower than 70%. Lower is better.
  • When cool, dry air rolls in later this summer and early fall, open the vents you have and consider adding more if humidity doesn’t drop rapidly to the 50% or 60% level without the dehumidifier running.

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