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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Locate your dryer vent wisely

Tim Carter Tribune Media Services

Question: My husband wants to vent our clothes dryer directly into our garage in an attempt to keep our cars warmer in the winter months. I think dryer vents should be directed outdoors. Can you settle this debate? Where would you vent the dryer, and what would you avoid when installing a clothes dryer vent?

Cindy R., Redondo Beach, Calif.

I get asked so often to referee these marital debates, I am thinking of buying a black and white striped shirt. Your husband should be congratulated for thinking of a way to use the waste heat from the clothes dryer, but his proposed method will cause some secondary effects that could end up costing you time, trouble and money. This may also be a building code violation in your area, as it is not a good practice to have penetrations in the wall between a house and the garage.

Along with all of the heat that would pour into your garage, you also get scads of water vapor. If you have ever seen a dryer vent belching out a plume of water vapor on a cold winter day, you know this might be problematic. All the liquid water that was in the clothes will get sent into the garage if your husband implements his idea. This water will undoubtedly condense on all of the cool surfaces in the garage, causing rust and corrosion on any unprotected steel tools or parts.

But the water vapor will also condense in places you can’t see. You may end up with water and mold issues inside your garage walls and in the attic space above the garage. Wood rot is a distinct possibility if this water vapor discharges into the garage for any length of time. Lint will be everywhere in the garage as well.

Venting a clothes dryer is a very misunderstood aspect of home building and remodeling. It’s critical to do it right. Many people underestimate the thousands of cubic feet of air that are expelled by a clothes dryer each time it dries just one load of clothes. This air must be exhausted outdoors, as your intuition told you. But this doesn’t mean you can’t capture some of the heat before you exhaust the air.

I always say to vent clothes dryer exhaust outdoors. You can do this sideways through a wall or up through a roof as hot air goes up with ease. The most important thing to do is read all of the written instructions that come with a clothes dryer and follow them to the letter. The instructions often describe in great detail the preferred pipe to use and the configuration of the pipe as it makes its way from the back of the dryer to the outdoors.

Almost every clothes-dryer manufacturer will tell you to use smooth metal pipe as the venting material. This pipe should be 4 inches in diameter and extend some maximum distance. Each manufacturer will state how long the vent pipe can be. You need to do some math as 90-degree fittings that allow you to turn corners must be accounted for in the calculation. A single 90-degree fitting usually equals 10 feet of straight pipe.

To extract heat from a simple clothes dryer vent, try to install the metal vent pipe so it is near or at its maximum length indoors. If you have the luxury of an unfinished basement, you may be able to run the metal vent pipe at a slope from the dryer to a window that is perhaps 20 feet away. The hot pipe radiates the heat directly into your basement along its entire length.

You may be able to fabricate a crude heat exchanger using some scrap sheet metal. But if you do this, be sure it is made with a door that allows you to open it to check for lint buildup. Dryer lint can feed fires, so you must always make sure your dryer vent is free of lint buildup.

It is very important that the vent be well insulated if it passes through a cool or cold space like a crawl space or attic on its way to the exterior. If the pipe is not insulated, water can condense on the inside of the vent causing leaks or poor dryer performance if the pipe becomes filled with water.