The best way to vent a dryer is to run rigid ductwork from the dryer’s exhaust port to the outdoors. When the dryer is located in an indoor location adjacent to an exterior wall, which is often the case, this usually involves making an opening in the exterior wall at least 12 inches (30.48 cm) above the ground, and 12 inches (30.48 cm) from external obstructions like decks or air conditioners. The hole is outfitted on the outside with a vent cap, from which ductwork is run to the dryer’s exhaust port. If a dryer will be located away from external walls, a system of ductwork leading from the dryer's location to an exterior venting cap must be installed to facilitate the venting process. The use of rigid, smooth-sided ducting is recommended wherever practicable to reduce lint buildup, which can lead to problems like impaired dryer efficiency and fires.
A standard household clothes dryer can remove up to 3 gallons (11.36 liters) of water from a full load of wash. This water is removed from the wet laundry by evaporation and then venting of the moist hot air out of the drying chamber. If the hot, moist air is allowed to flow into the environment around the dryer, however, the moisture will condense and accumulate.
The escape of moist dryer exhaust can cause severe structural damage if unabated, especially if the moisture accumulates behind the structure’s walls. Structural elements such as wooden studs and wallboard can absorb the moisture, losing strength and compromising the structure’s integrity. Wood can rot and mold can develop. Thus, most houses are constructed with ductwork that provides a passageway for dryer exhaust to leave the structure entirely. This ductwork leads to the structure’s exterior and is capped to prevent the entrance of either rainwater or animals.
To connect the dryer vent to exhaust ductwork built into the structure, flexible ducting is available. In the US, flexible ducting typically is made of wire-reinforced metallic or plastic foil four inches (10.16 cm) in diameter and is clamped onto the dryer's exhaust port. The flexible ductwork should be cut to size and the free end clamped onto a port protruding from the house’s dryer exhaust ductwork. The clamps can be either elastic clamps that look like very large rubber bands, or they can be metal rings that are screwed tight. Care must be taken to avoid crushing flexible ducting, which will reduce the dryer’s efficiency and could lead to heat buildup, lint accumulation and fire.
When installing a dryer in an apartment, there may not be access to internal ductwork to vent it. The most common way to vent a dryer in an apartment is to vent the exhaust out a window. This is done by building a frame cut to the window’s width and 6 – 8 inches (15.24 – 20.32 cm) high, and installing an external dryer port in it. The frame is installed by opening the window, setting the frame in place and attaching the flexible ductwork to it. This arrangement can be left in place or taken down and stored when the dryer’s not in use.