"Pico Rico" wrote in message
...

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?

In several modern countries, both fuel and utilities vendors provide
sample budgets, sometimes also national laboratories for building
standards, efficient energy policies etc.
--
Don Phillipson
Carlsbad Springs
(Ottawa, Canada)