"Bob" wrote in message
...
wrote:
We are planning on a new gas furnace next month. We have gotten
several estimates and some conflicting advice. One person told us to
get a 90% efficient furnace. It will require venting from the side of
the house. The second person said that these vents can freeze up in
the winter and cause flooding in the basement and possible carbon
monoxide troubles. He suggested the older type, an 80% efficient
furnace which can use our existing roof vent.


90% furnace vents freezing up and flooding the basement? Right. I'd
suggest you get another estimate to compare with the one from the first
person, and don't bother calling back the second person.

I've lived with a 90% furnace since 1985 here in St. Paul, MN, where it
does
get rather cold in the winter. Never had the intake or exhaust pipes on
the
furnace freeze up. I have had some neat looking icicles form around the
exhaust pipe in really cold weather from time to time, but it never
blocked
the pipes.

Only time a 90% furnace could freeze up is if it's installed in an
unheated
attic.



Apparently the water being sent out by the newer types is from
condensation? This surprised me since our house is always SO dry in
the winter that we need to use a humidifier.

The 90% furnaces use a sealed combustion chamber; outside air is brought
in
via one PVC pipe, heated and exhausted out the second pipe. The heat
exchangers pull so much heat out that the exhaust leaving the furnace is
only warm and it forms condensation, which is drained out via a hose. By
the way, the stuff that comes out is acidic, so don't drink it.

One advantage to the separate air and exhaust on the furnace is when it's
running it's not pulling air in around doors, windows and other leaks in
your house. Oh and the reason they call them 90% efficient is 90% of the
heat created is used to warm your house, with the remaining 10% going out
the exhaust vent.


As for the problem with freezing - if we went away for a month could
we expect to come back to a basement full of water? Naturally we
would want to set the heat down low (65 or so).

A basement full of water? Naaa. Maybe a few gallons if the drain hose on
the furnace was disconnected. Now if the furnace were turned off in
sub-zero weather, well, then you are looking at burst pipes.



The 80% furnace is cheaper but will require some type of air exchange
installed. Guess what we have doesn't meet code. That means that
getting the 80% won't really save us much money over the 90%. On the
other hand I don't want to have to worry about problems. That's why
we are getting rid of our old furnace in the first place.

When I had my furnace put in back in '85, I also looked at 80% and 90%
furnaces. Yes, there was a large price difference between the two, until
I
factored in that would need a flue liner installed in my chimney with the
80% furnace. Seems one contractor forgot to include that in his estimate,
but the company I went with pointed that out when I got quotes from them
on
both an 80 and 90% furnace. Also, you may need a fresh air intake for the
80% furnace so it can draw outside air when it's running. The air
exchanger
that you were quoted may take care of that, but they are expensive.


Advice and/or experiences would be much appreciated.

Hope this helps.
Bob.



I agree with Bob.

Never had a problem with a 93% dripping on the driveway yet.

Colbyt