Moisture can seep into your home in any of several ways. The soil around your foundation, surface-water drainage and damp outdoor air can all contribute to the problem. You and your family are also adding moisture through breathing and perspiring, showering and bathing, using the clothes dryer (especially those vented incorrectly to the inside of the home), washing dishes and other surfaces and, of course, intentionally, through the use of humidifiers.
Homes have access to more than one source of moisture. In many, this moisture causes problems only occasionally, but in some, problems are present nearly all the time. Prevention is the best bet; only when everything has been done to stop moisture from getting in should you rely on the dehumidifier to take care of excess moisture.
Sometimes floods or plumbing leaks can cause big problems in no time at all. Repairs deal with the source while industrial dehumidifiers are put to work cleaning up the mess.
A hygrometer can be used to measure relative humidity, so if you're unsure, it will let you know where there could be a moisture problem.
Make sure downspouts are directed away from the home's foundation, and keep gutters and downspouts clear of debris. Surface-water leaks can be avoided by sloping soil away from the foundation and giving outdoor plants no more water than necessary. Leaking outdoor faucets should be repaired. Groundwater leaks can be remedied by fixing walls and floors in basements or crawl spaces. A few other simple measures include running humidifiers only when needed, line-drying clothing outside and venting clothes dryers outside the home. A good bathroom fan should solve any moisture buildup issues stemming from showers and baths.
Keep windows closed as much as possible in hot, humid weather. Air conditioners with high latent-heat ratings will actually take water out of incoming air. In cold, dry weather, ventilation is the best way to reduce relative humidity.
When dehumidifying doesn't work
If reducing relative humidity doesn't fix moisture problems, wall or ceiling air barriers or defective insulation might be to blame. These can cause unusually cold spots in the house, which make room for condensation even if the humidity is below 50 percent. In this case, a professional will likely need to be called.