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 dwelling's attic. Tumble dryers are sometimes integrated with a washing machine, in the form of washer-dryer combos, which are essentially a front loading washing machine with an integrated dryer or (In the United States only) laundry centers, which stacks the dryer on top of the washer and integrates the controls for both machines in a single control panel. Often the washer and dryer functions will have a different capacity, with the dryer usually having a lower capacity than the washer. Tumble dryers can also be top loading, in which the drum is loaded from the top of the machine and the drum's ends are in the left and right sides, instead of the more conventional front and rear. They can be as thin as 40 cm in width, and may include detachable racks for drying items like plush toys and footwear. Ventless dryers Spin dryers These centrifuge machines simply spin their drums much faster than a typical washer could, in order to extract additional water from the load. They may remove more water in two minutes than a heated tumbler dryer can in twenty, thus saving significant amounts of time and energy. Although spinning alone will not completely dry clothing, this additional step saves a worthwhile amount of time and energy for large laundry operations such as those of hospitals. Condenser dryers Just as in a tumble dryer, condenser or condensation dryers pass heated air through the load. However, instead of exhausting this air, the dryer uses a heat exchanger to cool the air and condense the water vapor into either a drain pipe or a collection tank. The drier air is run through the loop again. The heat exchanger typically uses ambient air as its coolant, therefore the heat produced by the dryer will go into the immediate surroundings instead of the outside, increasing the room temperature. In some designs, cold water is used in the heat exchanger, eliminating this heating, but requiring increased water usage. In terms of energy use, condenser dryers typically require around 2 kilowatt hours (kW⋅h) of energy per average load. Because the heat exchange process simply cools the internal air using ambient air (or