Go with what your contractor says, it sounds like he knows what he's doing.
Rheem lets you use just an exhaust. They also let you downsize the last 18"
from 2" to 1-1/2" PVC in certain instances.
If you put in the bigger unit, the blower will produce more CFM, and
velocity of air out the ducts will most likely be offensive. Rheem Mfg.
bought out Weathermaker years ago. They might even be the same color now. No
buyer is going to notice that they both don't have the same name. I sell
Ruud because my wholesaler stocks that in my area. When they can't get a
matching unit, they go to other parts of the country for a Rheem.

"Jim Redelfs" wrote in message
...
Imagine all the added elbow room if the adjoining water heater was GONE
during
a furnace retrofit. Well, that's what I'm going to be doing (See Downsize
Water Heater ) in
a
little less than two weeks.

My contractor wants to DOWNSIZE to 75k from the 100k size of my
14-year-old,
conventional (spec) gas furnace. Of course, this will be done with a "90"
(or
better) model. He claims that the improved efficiency of the new furnace
will
compensate for the difference. Do you agree?

He also mentioned, after taking measurements TWICE, that I need an
18-inch-frame unit and that a bigger unit would require a reducing "boot",
which he represents as a compromise. What's with that?

Then there's the PVC vent(s) outside. He claims that it is legit to use
only
ONE - an exhaust line - that the furnace uses INTERIOR air for combustion.
He
represents this as a DESIRABLE way to EXCHANGE interior air with fresh.

I am old enough that this furnace may well be part a big part of the
resale
value of our home. He wants to install a "Weathermaker" furnace and a
Rheem
ac condensing unit outside. He says that the Weathermaker FURNACE is
virtually the same unit as a Rheem so this would be an up-front
cost-saving
issue ONLY, assuming he's right. What about resale then?

He further says that the condensing units are different and therefore,
recommends a Rheem unit outside.
--

JR