On Tuesday, January 27, 2015 at 6:07:34 PM UTC-5, Curmudgeon wrote:
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.

I'd be happy to see data that supports that. There are a lot of people
with fuel bills of $1500 a year. If they save 20%, that's $300 a year.
In ten years, it's $3000, about 50% more than the cost of the furnace
equipment to begin with. I replaced my 27 year old nat gas furnace
4 years ago and have been saving 40%+, Ed reports similar with a boiler.
I'm saving about $300 a year. The most costly repair, would be the
heat exchanger. All the systems I looked at, the heat exchanger was
either warranted for 20 years, lifetime, etc. Not saying you won't
have to put some money into an aging furnace, or that a high efficiency
one doesn't have more parts that can fail, just that I haven't seen
any real data to support that it's going to wipe out staying with a lower efficiency furnace.




A co-worker paid $260 to have a safety switch replaced on her high efficiency furnace last season.

Yes, there are more safety devices on modern high efficiency furnaces,
so there is more possibility of one failing. But I also wonder how
many safety switches there are on a new 80% furnace now too? I've
got 4 years now with a Rheem 93% furnace, not a single problem.


This year was another $610 for a draft inducer.
In my opinion, high efficiency furnaces are poorly engineered junk.

If she paid $610 to have a draft inducer installed, I'd say the
more likely problem is that she has a service company that is
screwing her. I'd also point out that a lot of stuff today doesn't
last as long as it used to. I think in many cases folks are comparing
the lifecycles of 40 year old furnaces to modern ones. I'd be
surprised if a new 80% furnace lasted as long as one did bought in
1970 too. In other words, you have to compare the problem rate of
a new 80% with a new 93%+.