Washer dryers may be stackable or side-by-side. In order to be stackable, the washer needs to be a front loading washing machine. A front-loading washing machine will have a smooth flat top which will allow you to place the dryer on top of it. The controls of the dryer will be placed at eye level allowing you easy access of the controls. The advantage of buying a stackable model is that it occupies the space of only one washer.

The difference between having separate stackable washer dryers and a washer dryer combo is that the latter will usually use the same drum to dry clothes. The benefit of these models is that they save space and no venting is required.