"Robert Gammon" wrote in message
...
Al Moran wrote:
On Sat, 16 Sep 2006 21:39:14 GMT, "MLD" wrote:



You are not taking into consideration the fact that the 80% furnace
uses
inside air for combustion and the 90% furnace brings in outside air.
The
inside air has already been heated, that has cost you $$$ and you're
throwing it up your chimney . This air has to be replaced and the new
air
is coming into your house from the outside--cold air that has to be
heated
to room temperature--more $$$$. It gets into your house through
cracks,
windows, under doors--so your house gets drafty. All this newly heated
air
has to be humidified because it is going to be very dry. My point
being
that the $$$ difference between the 80% and the 90% furnaces is more
than
the 10-12% in furnace efficiency.
MLD




That's the dumbest thing I've heard in awhile. That air your talking
about that is already heated and gets put up the chimney, did you ever
stop to think that it must pass the burners to get there in the first
place? Now if by chimney you mean the real chimney, any idiot knows
to close the damper when the fireplace is not being used. As for a 90%
furnace getting air from outside, bull****. They can get air from the
living space also. Stick with something you know cause hvac ain't it!

Most, but not all new 90% furnace installations DO bring in outside air,
in a PVC pipe to supply the burners, particularly in new custom homes as
extra attention is paid to proper sealing.

Manufacturers have recommended this practice for a LONG time, same as
fireplaces that bring in combustion air from the outside so that you
keep the doors closed most all the time.

Once again--the air used for combustion on an 80% furnace is supplied by air
that is already in the house. A 90% furnace brings in air from the outside.
In my search to install a new furnace I didn't see one manufacturer that did
it otherwise. The exhaust air from a 90% furnace has just about all the heat
squeezed out of it-- that's why it can safely be vented outdoors. You can
put your hand in the air stream and it feels luke warm. If you vented the
90% exhaust gases into the chimney you'd have a problem sooner or later.
Why? First of all there would be problems creating the proper draft because
of the relatively cool air moving up the chimney--not too good to have
poison gas reentering the house. Second, because of the condensation that
would form in the chimney. I don't know who Al Moran is but I do know that
he isn't too bright.
MLD