How to properly vent a clothes dryer

For savings and safety, don't neglect ducts

Your clothes dryer is one of the hardest-working appliances in your home. It’s also a fairly basic appliance in how it operates, and if it’s properly vented and maintained, it should give you years, even decades, of reliable service.

But "properly vented and maintained" is the catch. Because a dryer is such a simple appliance to install and operate, many people don’t give it much thought. They set it in place, plug it in, vent it through that pipe coming up out of the floor — typically with the wrong type of vent hose — then forget about it. And there it sits, slowly degrading in performance, using up increasingly greater and greater amounts of energy, and becoming a bigger fire hazard with each passing day!

Dryer operation 101

When you put in wet clothes and activate a drying cycle, here’s what happens: A fan is activated to draw air into the dryer through the front. The air is heated by a heating element, then passed through the drum, which is rotating to circulate both the clothes and the air. The hot air draws moisture from the clothes, and is then directed through the dryer’s door and through a lint screen. A fan pushes the now moisture-laden air into a duct that exits through the back of the dryer.

The two important things for you to know in all that is that the air in your dryer is both extremely moist and also — despite the lint trap — still full of fine lint. If you don’t handle that air and that lint properly, it’s inevitably going to lead to problems.

Lint that builds up in the dryer and in the vent pipes will retain moisture. Now every time your dryer operates, it has to work harder and harder to dry the clothes, and to push the wet air past the wet lint in the lines. That lengthens the time your clothes takes to dry, which, plain and simple, is throwing away your hard-earned money. It also shortens the life of your dryer. Besides that, the moisture in the lines is a breeding ground for mold, and it prevents your clothes from being and smelling completely clean. Finally, lint further along the lines that dries out is extremely flammable, and is one of the leading causes of house fires.

Proper dryer venting

At the rear of your dryer is a 4-inch diameter vent, which is where the internal fan is going to push all that wet air. It’s up to you to make sure that vent pipe gets properly connected to the outside, and there are three basic components in the dryer venting system that you’ll want to set up in order to do that correctly:

1. The duct between inside and outside: From the inside of the house, you’ll need a duct that leads to the exterior. In homes with a crawl space or a basement, this is usually run under the floor, elbowing up through the floor to terminate right behind the dryer. If the dryer is located on an exterior wall, you can simplify the installation and shorten the duct run by simply going right through the wall. For dryers located on a second floor, or on a concrete slab, duct pipes are often run vertically into the attic, then out through a side wall.

Use 4-inch smooth-wall galvanized or aluminum duct pipe that’s made for this purpose, not flex duct. Flex duct traps both lint and moisture, and is very hard to clean. Smooth-wall pipe is typically sold in 5-foot lengths, with one end crimped so that it slides easily into the uncrimped end of the next pipe. Seal the joints using a good-quality metallic seam tape — not regular cloth duct tape. For changes in direction, use adjustable elbows.

Remember that the dryer fan has only a limited ability push the wet air, so keep the length of the duct run as short as possible, with as few elbows as you can. Support the ducts with strapping to avoid sags, and try to angle the run down from the dryer to the exterior to prevent any moisture from accumulating in the pipe. Refer to the dryer manufacturer’s specific instructions for their suggestions on maximum ducting lengths and other information.

2. Exterior cap: At the outside of the house, whether you pass through a wall or a foundation, you’ll need to terminate the duct pipe in a cap. The best type of cap to use is one with a set of three or four overlapping damper flaps, as opposed to one large one. These smaller flaps will open easily when the dryer is in operation to allow air to exit, then close to keep cold air and pests from entering the house.

3. Interior flex connection: Behind the dryer, you’ll need a connection between the dryer’s vent pipe and the duct pipe that’s coming through the floor or the wall. In order to make it easier to pull the dryer out for periodic cleaning, this connection needs to be flexible — it’s the only flex line in the entire setup. To avoid potential fire hazards, this flex line needs to be aluminum, not the inexpensive white vinyl.

Keep it clean

Now that you have everything properly set up, it’s crucial that you keep everything clean. Remove and clear the lint trap with every load of laundry. Every couple of weeks, rinse the lint trap in the sink and clean it with a fine brush, like an old toothbrush, so that fine lint particles don’t build up on the screen.

Even with the screen, lint still accumulates in the duct system. To keep your dryer working correctly and to avoid wasting money, you should clean the duct system itself every couple of years — more if you have a large family and use the dryer a lot. You can probably clean a short run yourself, such as those that pass straight through an exterior wall. Longer runs should be professionally cleaned by a company that has the proper vacuums and brushes; check online under "lint cleaning" or "dryer cleaning," or call a local appliance repair shop to check for recommendations in your area.

Remodeling and repair questions? Email Paul at paulbianchina@inman.com. All product reviews are based on the author’s actual testing of free review samples provided by the manufacturers.

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