I've been brewing outside in the winters of Northern Illinois (near the WI border) for a couple of years. 12 gallon boils with a jet burner are not a problem. I will mention that during Jan or Feb last winter my CFC was running really slow and I finally figured out that with the wind chill it was freezing the beer solid in the hose post-chill. I cut back the water flow a bit so it wasn't as effective and the slightly warmer beer went into the fermenter just fine. If you have the option of using an immersion chiller in the coldest weather, it might outperform either a plate or CF chiller.