Went through this about 2 years ago. Firstly, define "efficient." If
you mean over 90%, as in one of those two stage furnaces with PVC
handling moisture then you are consigned to having to use a variable
speed DC motor (there are no variable speed AC motors, only speed
settings you set manually at installation) that will cause RFI because
it is run on variable duration square wave DC. You will have to have
the HVAC contractor install a manufacturer supplied hush kit, or do it
yourself. The hush kits are over priced and many contractors are
unfamiliar with them and RFI.
Or, you can do what I did and get a single stage 80% efficient furnace
that runs on an AC blower and accept 10% less efficiency and get on
with life. Mine is around 80K BTU, not extremely big. There are
larger ones, or were. I went with American Standard, an Ingersol Rand
brand name. There are around three companies that make all the
furnaces; IR is one of them. I've heard the AC blower furnaces are
going to be history in a few years after which they'll all be high
eff. DC because gov't is obsessed with this, but that's another topic.
73
Rob
K5UJ
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