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Can an 80% efficiency furnace be installed in an attic in zone 6B?

I just bought a house with a 97% efficient furnace in the attic; I live in zone 6B. After several service calls the contractor who installed the furnace -for the previous owners-told me that this furnace should not be in the attic in Wisconsin due to condensate freezing problems-which has happened twice since I moved in in October of this year. After some research both with local contractors and on the internet I came to the conclusion that an 80% efficient furnace may be a viable option until I can save enough money to have a furnace installed in my basement with new duct work being run under the floors. The contractor, however told me that this is not an option due to venting concerns. He suggested moving the furnace to the basement and running ductwork from the furnace in the basement to the existing ductwork in the attic. I am not an HVAC guru, but this solution seems like overkill. Several HVAC specialists have called in to question the integrity of a contractor who would install such a furnace knowing it would fail, so I am leery of accepting his advice at face value I would just like to know my options at this point.

Asked by Anne Sullivan
Posted Thu, 12/26/2013 - 18:23

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Anne,
A furnace should not be installed in an unconditioned (vented) attic in Wisconsin. Period.

If you can afford the work, you could install spray foam insulation on the underside of your roof sheathing to bring your attic inside the conditioned space of your house. This solution will only work if you have a sealed-combustion furnace.

If you can't follow that recommendation, then your furnace belongs in your basement.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 12/27/2013 - 07:18

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