I was able to get a 410a unit installed last year. The installer and I were discussing the new equipment with the new refrigerant that has LP in it. He was not real happy about it. One of the quirks about it, because it is somewhat flammable, the air handler (inside coils) cannot be installed in a confined space. My AC closet would have had to have vents cut in the door as well as opened up to the attic. Not talking about the return....this is just for the unit itself. How inefficient that would be. Not good with a hot Alabama attic.