Did an Energy Audit for a friend yesterday, and found the most unusual installation: A 4" insulated duct directly from the outside air to the cold air return. The hot air coming out of the registers only got about 85-95 degrees, which seems a bit cold to me. The exterior air temperature was about 20 degrees, which would have an alarming affect on the temperature of the heated air. The furnace seamed to run allot and do take about 10 minutes to raise the temp 1-2 degrees.
This is a High efficiency furnace, properly vented, in the tightest conventional house I have ever seen. Did the furnace guy install this to allow more fresh air in the house? I seriously think it is overkill, and should be eliminated.