DIYbanter - View Single Post - high efficiency gas furnace advice please

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.

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.

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).

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.

Advice and/or experiences would be much appreciated.

Be sure to check whether it really needs to go out the
wall. I just had a new high efficiency furnace put in
and it uses a vertacle flue that goes through the roof
the same place the old one did. It has a special
concentric flue pipe. There are 2 pipes, one inside the
other. The flue gas goes up through the inside one and
combustion air comes down through the outside one.

As far as freezing up is concerned, in colder climates
the drain line should be connected into your sanitary
sewer. If it runs outside the drips may freeze up and
back up water into the furnace. In mine there is a
float switch that detects a backup and turns everything
off. The company that installed it tells me that they
have never had any problem around here, so they ran it
through the wall outside. Someplaces there is
apparently a code requirement for the sanitary sewer
connection.

Bill Gill