Can you put a 95 percent HVAC in the attic?

[Christian Bors]

My contractor wants to put a 80% efficiency furnace in the attic due to cold temperatures in the winter.  He is concerned with 95% can freeze.  I am assuming he's talking about the condensation?  As far a price, he said the difference is like 100$ so he doesn't care which unit to use.  The property is located in PA and sometimes are winters can be harsh.  What would you suggest?  Also, the unit has to go in the attic.

Thanks,

CB