I'm having a high efficiency condensing furnace put in our second floor soon. We're going to insulate the condensate line but I'm wondering why the need for a trap? I understand why we do that in a toilet or sink, to keep sewer gases from backing up unto the house. But why a furnace (or A/C) condensate drain that drains out into the open (fresh) air. Seems to me that deleting the trap would eliminate the major freezing concern with a condensing furnace?