We have an older home with a separate high efficiency furnace for the second floor. It sits on a floored area of the attic. We have virtually no insulation and I've gotten various recommendations from contractors. The concern is that the furnace need to be in a heated area. Right now, without insulation, the attic is somewhat heated. One contractor suggests walling off the furnace area and insulating the rafters with foam to make a warmer area for the furnace. But I'm concerned about blocking air circulation if we do this. Is there a good solution?
How big is the attic? One solution is to take 2, 3 or 4" insulation board (R13 to R25) and affix it to the rafters. This would basically make your attic conditioned space (and thus the air between the foamboard and your ceiling will also add R-value) while also protecting your ventilation pathways. A board with a radiant barrier on each side would be a plus and be sure to seal between the boards. If you Google "Superattic", you'll find a better explanation. NOTE: On a DIY basis, it's not very expensive. But if you hire someone and your attic is big, the cost can add up.
so high efficiency furnace you have pvc piping for venting and a condensate drain for furnace? if this is correct. i would frame and insulate walls for the furnace in leaving a good access, then have a opening in the plenum cut in so you can keep heat in. otherwise the condensate or worse yet the secondary heat exchanger freeze up.