[phillyg]

You're correct in everything you stated, but the single return at the steps in Montanas can be blocked for summertime since its only the cold air return for the furnace. It has nothing to do with the roof-mounted ACs. I can feel warmth when I use the steps. I don't know how effective it is to block the return, but I can't believe it would hurt anything unless one forgets to unblock it during furnace use.