"Brian E. Clark" wrote in message

Now, the trouble is that he couldn't find the source of the
"leak." It seemed to him that the burned gases weren't reaching
the flue properly. It could be that there's a blockage in the
heat exchanger or the exhaust pipes. Or there could be a crack
in the heat exchanger itself. (It's just not possible to get a
full view of the exchanger without taking part of the furnace
apart.)

Or it could be a bird nest on the of the flue.


I'm trying to decide on options. Should I just get a new
furnace? Or should I pay the furnace company a fair bundle to
disassemble the unit and look for a block or leak? Will
exchangers that are approaching their 70th birthday even come
apart, so we can look for blockage?

At that age, it is risky to try to disassemble anything. Rust, corrosion,
frozen bolts,


If a new unit is need, what's the ballpark price in the
Pittsburgh region?

I can't help you.

(The old, 1938, ratings were 200,000 BTS in
and 160,000 BTUs out. But several furnace folks have told me
that a new unit wouldn't need to be anywhere near as robust,
because newer furnaces lose less of their heat up the chimney.)

True. Your heating contractor can do the calculations to determine just how
big a unit you need.