I am wondering if during the coldest windy nights did your existing furnace EVER run for 30+ minutes?
I know that when -20F with 30 MPH winds the heating equipment get a good run. You do not want to be short capacity in Minn. when temps drop below design temp. I would get a 2 stage system so the heat will run constantly and go to high fire when exreme temps hit.
Also I hear the 90+ units are not as reliable, but I hat be incorrect since I am a Refrigeration man. I do know you cant go without heat for more than a few hours in Minn.
Ask the contractors what they recommend for the severe winters you have! They are the ones that have to make it work on the cold winter night when it is -20.
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