Pico Rico wrote:
A friend has a house in the mountains. No A.C. The furnace is as old as
the house, probably 1965 or 1970. Are new furnaces more efficient in their
use of natural gas, and thus "pay for themselves"? If so, how does one
calculate the anticipated savings and pay back period?


I put in a coleman THE about 25 years ago and the efficiency was 90%.
This unit was inexpensive (actually designed for a housetrailer, but it
was big enough for our house). I think the trick was they passed much
more air through the heat exchanger. It needed no chimney, but the air
coming out of the registers actually felt cool, but there was so much of
it that it heated the house. My feeling is that you can compare
efficiencies, but you cannot calculate payback periods because gas
prices vary and weather varies. All you can do is keep track of your
costs and calculate payback period retroactively. Anyway, because of
abnormal weather and changes in gas prices, that unit paid me back in
just over one year. I don't expect to ever match that performance
again. It had some design problems and after many years, I was seeing
the repairman too much. So this year I replaced it with a Bryant said
to be 95.5 efficient. The biggest change I noticed is that it has air
from outside the house pumped in and used for combustion. As a
consequence, we don't have outside air in the house, and the air coming
out of the registers is much warmer. It also has a high efficiency
multi-speed blower which comes on at a lower speed during some of the
furnace's idle time to circulate the warm air in the house. I haven't
had it long enough to calculate how much, if any, it will save us, but
the increased comfort is worth a lot. Now I'm looking at adding a heat
exchanger to get some fresh air into the house