A clothes dryer, tumble dryer, drying machine or dryer is a powered household appliance that is used to remove moisture from a load of clothing and other textiles, usually shortly after they are washed in a washing machine. Clothes may also be dried by natural evaporation and, if available, sunlight on an outdoor or indoor clothes line or clothes horse.

Many dryers consist of a rotating drum called a "tumbler" through which heated air is circulated to evaporate the moisture, while the tumbler is rotated to maintain air space between the articles. Using these machines may cause clothes to shrink or become less soft (due to loss of short soft fibers/lint). A simpler non-rotating machine called a "drying cabinet" may be used for delicate fabrics and other items not suitable for a tumble dryer.

Tumbler dryers continuously draw in the cool, dry, ambient air around them and heat it before passing it through the tumbler. The resulting hot, humid air is usually vented outside to make room for more dry air to continue the drying process. This design makes no effort to recycle the heat put into the load, and thus is considered environmentally wasteful. Nevertheless, it is simple and reliable, and therefore has been widely used.

Improvised methods of salvaging this heat for in-home heating, by use of inline vent boxes equipped with a flapper valve to redirect moist heated air to indoor areas, will also increase humidity within a dwelling. Although this may be beneficial in dry winter conditions, excess humidity from these devices increases likelihood of mold, mildew, and bacterial growth inside a home. Indoor venting may also be against local regulations. Gas dryers must always be vented outdoors, as the products of combustion are mixed with the moist air. Building codes and manufacturers' instructions usually recommended that dryers vent outdoors. An indoor lint trap kit poses a similar concern of increased humidity within the dwelling.

"Long run" dryers have an additional fan inside to boost the exiting moist air through longer sections of vent pipe, as in apartments or dwellings where the vent cannot make a short direct connection from the dryer to the outside.

Beyond issues with venting exhaust, other improvised efficiency efforts with conventional dryers attempt to harvest an input source of pre-heated air rather than using the conditioned air of the living space. One notable source of heat to pre-heat dryer air is to install ductwork allowing the device to suck hot air from a d