Short instructional clip (YouTube) by Derek Cole explaining HVAC air return placement: make returns large and multiple so the system draws conditioned, filtered air from returns rather than unconditioned air from crawl spaces, attics, or outside. Controlling return airflow saves energy and reduces system workload.
Chapters
You want to make it as easy as possible for the air to get back to the unit. So the bigger the return and the more you have in these different locations where it can be closed off, the better, because you want to make it very easy. Otherwise, the unit is going to get the air it needs. It's going to suck it through the crawl space to the attic, to the outside. It's going to get the air it wants to get to operate. But you want to control it. You want it to be cool or warm, filtered air from your return, not from the outside, which is unconditioned air. Right. So that'll save you energy, and the unit will not have to work as hard to get the air back to it.