Clothes dryers are designed to remove moisture from clothes and other textiles by heating air, using either electricity or gas, and passing the heated air into a tumbler. Clothes dryers are also differentiated by their capacity: standard (4.4 cu. ft. and greater) or compact (less than 4.4 cu. ft.). Clothes dryers are typically manufactured with a vent to which an exhaust is fitted, but vent-less dryers are common in areas where space for venting is restricted, such as apartments or mobile homes.
Congress set the initial clothes dryer standard in 1987, outlawing constantly-burning pilot lights in gas dryers. DOE published a final rule in 1991 establishing the first performance-based standards for clothes dryers, which became effective in 1994. The efficiency of clothes dryers is currently measured by the energy factor (EF) in lbs/kWh: the EF standards are 3.01 for electric dryers and 2.67 for gas dryers. In July 2010, efficiency proponents and manufacturers agreed to jointly support clothes dryer standards that would reduce energy use by 5%. DOE published a direct final rule on April 21, 2011 that reflects the standard levels in the consensus agreement, and on August 24, 2011, DOE confirmed adoption of these standards. The standards are based on a new metric, combined energy factor (CEF), which incorporates standby energy consumption. DOE estimates that the new standards will save 0.39 quadrillion Btus (quads) over 30 years and yield a net present value of $3 billion at a 3% discount rate. The new standards took effect January 1, 2015.
The assumption for a long time has been that there is no significant variation in energy use among dryers and that there is little potential for energy savings as a result. However, it has become clear that there is a significant flaw in the test procedure: it requires that the dryer be stopped before it automatically shuts off and essentially assumes that all dryers have equally effective controls for determining when to terminate the cycle. As part of the consensus agreement, efficiency proponents and manufacturers agreed to jointly support a change to the test method to capture the effectiveness of automatic termination controls (ATC). DOE proposed such a change to the test method in the test procedure proposed rule issued in June 2010, but DOE ultimately decided not to adopt the change. In August 2011, DOE reopened the test method rulemaking to further research the effects of (ATC), releasing a final rule in August 2013, modifying the test procedure to more accurately measure the effects of ATC.
Almost 80% of U.S. households have a clothes dryer and, of those, about 80% utilize an electric clothes dryer. Technology options for improving the efficiency of clothes dryers include increased insulation, improved air circulation and drum design, and recycling of exhaust heat. Improvements to clothes washer efficiency can reduce dryer energy use by reducing the remaining moisture content (RMC) of loads and therefore the amount of water that a dryer needs to remove.