Have a ­moisture problem in a basement or crawl space? A contractor might recommend an “exhaust-only dehumidifier,” claiming that its low electricity use relative to conventional dehumidifiers will save you money in the long run despite up-front costs that can top $1,000. In fact, those energy savings are an illusion—and these “dehumidifiers” don’t actually do any dehumidifying. 

This product, also called a “basement ventilation system,” is essentially just an expensive exhaust fan that sucks air out of damp basements or other spaces and expels it outdoors, similar to a window fan or attic fan. (Brands include EZ Breathe and Humidex.) This causes drier air from upstairs to be drawn down into the basement, which in some cases can eliminate musty odors and humidity problems as promised. However, although these fans consume much less electricity than conventional dehumidifiers, they do so by forcing your HVAC system to work harder. The air that’s drawn down to the basement is replaced by outdoor air pulled into upstairs rooms through cracks and door gaps—additional air that your HVAC system must heat or cool. The extra HVAC effort required to do that will greatly reduce or eliminate any energy savings, and it could shorten the life of your HVAC system. 

What’s more, if the air upstairs is humid—perhaps because you don’t have a whole-home air-conditioning system…or you sometimes open windows rather than run your air conditioner—a ventilation fan can’t solve your basement ­humidity problem. It will simply replace humid air with different humid air. 

What to do: If your basement is damp, use a condensing dehumidifier. Therma-Stor’s Santa Fe line of dehumidifiers is extremely energy-efficient and is the only major brand that provides effective air filtration. They’re expensive—typically $1,200 to $2,500 depending on size—but that’s not much more than many exhaust-only dehumidifiers. 

If you don’t want to spend that much, a standard freestanding $200 to $300 condensing dehumidifier from any well-known appliance brand is likely to be a more effective choice than an exhaust-only dehumidifier. Choose one that’s ­Energy Star–certified to minimize electricity bills. Wash the bucket, clean the filter screen, and wipe down its coils regularly to avoid mold and mildew growth.