Crawl spaces are never alike and you just never know what you will run into. Zeus is a large unit and needs some room to install behind a foundation vent. At times the plumbing lines, electrical wires, or ductwork can infringe on the needed space. The adapter provides some flexibility.
The East Coast and the West Coast have different size foundation vents. The East Coast vents are 8”x16”, the size of a cinder block. The West Coast has 6”x14”. We make adapter outlet size 6"x14" so they will work on the West Coast and East Coast.