Kurt, I actually ended up researching this a while back, Chicago's greatest recorded snow depth was 29 inches of snow on Jan. 14, 1979, so to meet the 12" rule in Chicago the vent terminal should be at least 41 inches above horizontal external surfaces. That assumes a lack of snow drifts. You know we get 'em 3'-4' high, if not more, easy. Back as a service manager for a builder, time when the first generation high-efficiency furnaces were installed, I got a call from a neighbor to a house we built that water was coming out of the front door. Turns out the homeowner was in Florida, and didn't know the *low* exterior flue our heating "expert" installed was covered with a snow drift and the furnace couldn't start. That, and the below-zero temps told the story; frozen and burst pipes throughout. As I recall, the house was a week out of warranty.