Venting Your Dryer Outside

William Kibbel III, The Home Inspector

I've had my dryer venting into my home for about 8 years. When selling my home, the buyer's inspector said it was unacceptable and now the buyer wants me to pay to install the vent to the outside. It's not even a gas dryer, it's electric. They even sell boxes with screens for this purpose. We're paying for the heat from the dryer, and I think it's fine to keep it inside. What's with this inspector?

Having a dryer vent into a home is not a good idea. All mechanical codes and manufacturers' instructions state that dryers must be ducted "to convey moisture to the outside of the building" for good reason.

The most consistent issue that I find is that the warm, moisture-laden air moves up through a home until it reaches the attic. It then condenses under the roof sheathing during the winter months. At first, it just leaves some black spots (mold), and then the entire underside of the roof turns black. Eventually, the roof sheathing starts to look like shredded wheat. Try this experiment--every time you do a load of laundry, pour 1.5 cups of water on a piece of plywood.

The winter is the worst time to dump that much moisture into a home. That's when it moves up through the home and condenses on cold surfaces causing the conditions I've described above. Just because the air inside a home seems "dry" in the winter doesn't mean that all the moisture discharged from a dryer magically disappears. Warm air can hold a lot of moisture. It retains most of the moisture until it condenses. When heat in the air is lost, most of the moisture in the warm air is still there. I've seen hundreds of homes with delaminated and even rotten roof sheathing, always worse under the north slope of the roof. It's always in homes that either don't have the dryer vented out, no exhaust fans in bathrooms with showers, or a really wet basement or crawlspace (and a couple with indoor swimming pools).

I'm aware of the gadgets marketed with the claim that you can "safely" vent a dryer indoors. They're just lint traps, using the surface of water in a reservoir to attract lint. Some just slip a pair of pantyhose over the dryer outlet to filter out some lint. There are many other products and devices available in hardware stores and home centers that are not permitted by codes to be installed in homes. They're in the stores because building codes aren't enforced at the product manufacture and distribution level. They're also in the stores because folks buy 'em.

Then there's the issue that some lawyers and many in the media are buzzing about -- mold. I often find homes with too much interior moisture have stuff growing where moisture can condense and there is little air movement. The common locations, other than attics, are the bottom of walls at outside corners of the home and the walls in stuffed-full closets.

About the Author
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.

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