This is a test of commonsense. Complete the next sentence:

How to stack a washer and dryer 
Choose compatible appliances. 
Theoretically, you could stack any dryer on top of a washer, as long as it fits. However, you could void the warranties on both appliances by doing this.
Instead, look for washers and dryers that are designed to be stacked together. Usually, this means having a washer and dryer of the same brand.