Im having the same issues. I live in Alberta and its been around -35 to -42 the past few days and my 3€� intake keeps getting frost built up in the inside until my furnace shuts off or just blows cold air. Can I still increase the pipe diameter as soon As it leaves the house? It does have a 90 facing down and slightly away from the exhaust that goes straight out. Im getting tired of cleaning the frost out 3-5 times in 24 hours including the middle of the night.