 is for your HVAC system. If you've got pets and it's coming through a floor register where maybe it's grabbing all the stuff on the hardwood floor, sucking that in, that's one thing. If it's in the ceiling, sometimes you'll get less dirt, but you're not going to get that same airflow down below, and so that won't pick up that dirt. It does a little bit better job, but really, this comes down to having a great air filter that someone designed specifically