Venting Your Dryer Outside Your Home It is important to vent your dryer to the outside of your home. Here's why: A typical 12-pound load of laundry weighs about 20 pounds when it emerges from the washer. That means your dryer has to dispose of about a gallon of water with every load. Because of all that moisture - which could cause mildew and other problems inside your home - exhausting the dryer to the outside is recommended. There are several types of ducting materials available, listed below in order of preference: Rigid metal (aluminum or galvanized steel) - strongly preferred Flexible metal - acceptable Flexible thin foil - unacceptable Flexible plastic - unacceptable Facts To Consider Underwriters Laboratories Inc., an independent testing agency that helps set national safety standards, requires that dryer manufacturers "include explicit instructions specifying that only rigid or flexible metal duct should be used for exhausting, unless the appliance has been investigated for use with nonmetallic duct." Maytag and other major dryer manufacturers recommend against the use of plastic flexible duct. Although plastic flexible duct (cheap and easy to install) might seem like just the thing for exhausting a dryer, it isn't. This type of exhaust duct, which resembles a plastic-covered slinky toy, is not recommended for several reasons. Recommendations Prior to Venting Your Dryer Read the manufacturer's installation instructions. If at all possible, use 4-inch diameter rigid aluminum or rigid galvanized steel duct. Do not use smaller duct. If flexible metal duct must be used, use the type with a stiff sheet metal wall. Do not use flexible duct with a thin foil wall. Never use plastic flexible duct. Do not exhaust the dryer into any wall, ceiling, crawl space or a concealed space of a building, gas vent or any other common duct or chimney. Keep exhaust duct as straight and short as possible. Exhaust systems longer than the manufacturer's recommendations can extend drying times, affect appliance operation and may collect lint. These recommendations may vary somewhat for various dryer brands and should be checked when installing the dryer. The exhaust hood on the outside of the house should have a swing out damper to prevent backdrafts and entry of wildlife. Never use an exhaust hood with a magnetic damper. The hood should have at least 12 inches of clearance between the bottom of the hood and the ground or other obstruction. The hood opening should point down. Never install a screen over the exhaust outlet.