Two types of products fall under the washer-dryer combo heading: laundry centers and all-in-one washer dryers. These laundry appliances typically are used in homes where space is an issue.
Often found in apartments, condominiums and other multi-family housing, laundry centers are the more common option. They're also known as stacked washer-dryer units.
Rather than consisting of two separate components, a laundry center is just one appliance, with a top-loading washer on the bottom and a gas or electric dryer on top. It can be full sized (27 inches) or compact (24 inches).
With an all-in-one washer-dryer, clothes are washed and then dried in the same tub. These products have been more popular outside the United States, where homes are smaller and many homeowners prefer to line dry most items.
In addition to being used in apartments, condominiums and other multi-family housing, all-in-one models are good for homes that do not offer dryer venting to the outdoors.