On 1/27/2015 4:52 PM, 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?



If your fuel bill is $1000/yr, an 80% efficient furnace would use $800 to heat your house and $200 would go out the exhaust.

If you bought a 98% efficient furnace, your fuel bill for the house would drop to $816, $800 to heat your house and $16 up the chimney.

FWIW, don't count on saving any money over the life of the furnace though. High-efficiency furnaces break down a lot as they age.
Any fuel savings you accrue today will be eaten up with expensive repairs after the furnace is 10 years old or so.

A co-worker paid $260 to have a safety switch replaced on her high efficiency furnace last season. This year was another $610 for a draft inducer.
In my opinion, high efficiency furnaces are poorly engineered junk.