Originally Posted by Marty S.
Perhaps beenthere knows the reason for one high and one low. I know they're required to be within 12" of the ceiling and 12" of the floor but nobody ever explained why two are needed instead of one.
Its been a while since I had to remember why they want 2. So I could be wrong.
Its a left over from the old days. When the theory was that the high vent/intake would provide the dilution air for the old furnaces and boilers, and the low vent/intake would provide the air for the actual combustion. It was thought that a low only, would cause an updraft outside of the burners and cause a flame roll back. Of course, it never actually works that way. And 2 opening aren't required with every type of combustion air intake method.