A washer dryer combo takes up the space of just one of these.

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Types of Washer Dryer Combos

There are two types of all-in-one washer-dryer combos -- vented and ventless. "We have a vented version that we sell mostly to our marine and RV markets, but our ventless version is the one that is most common for use in high-rise apartments and condos, that type of thing," says Lee.

A vented unit basically works like a regular front-loading washer and a regular dryer. The wash cycle includes tumbling the clothes with water and soap until they're clean, then spinning them to help remove some of the excess water [source: LG Electronics]. For this drying system, the unit takes in air from the surrounding room and heats it up [American Gas Association]. This heated air is then spun with the clothes. The air picks up moisture, producing steam, which leaves the house via the vent. The system then takes in new air from the surrounding room and heats it up again to restart the process.

Alternatively, a ventless unit is a unit that doesn't require an outside exhaust. "There really isn't any washing difference; the main difference is on the dry side," says Lee. "The machines use a condensing drying system, and it works like a dehumidifier."

In a ventless system, wet clothes start in the drum. A condensing chamber, which can be plastic or metal, is cooled. Then the air inside the dryer drum is heated. As the drum spins, the interior heated air takes up moisture from the wet clothes. This moisture-laden air is then circulated through the cooled condensing chamber, which produces condensation, or a change of the moisture in the air into its liquid form of water [source: Lee]. The condensation then leaves the unit by the water drainage tube. The dry, hot air is then recirculated with the clothes, and the process repeats itself [source: Creative Laundry Systems, Inc.].

Whether you choose a vented or ventless unit, all-in-one combination units offer a range of program options to best fit your fabric care needs. You can wash and dry your clothes in one process, or you can also set the units for a "dry only" or "wash only" cycle [source: Equator Advanced Appliances]. Units also offer a range of settings, including delicates, timed drying and extra rinse [source: Creative Laundry Systems, Inc., Equator Advanced Appliances, Summit Appliance].

So how efficient are washer dryer combos?