My oil furnace is 26yrs old & running fine right now.

The combustion chamber looks good-- the bricks are solid - the plenum
was taken apart for a thorough cleaning last year & it looks good- and
there is no rust on the outside of the furnace.

But I know something major will break one of these days [last problem
was a limit switch 3 years ago- the air circulating fan the year
before- -- 5 yrs before that a transformer. These haven't been
major problems and I replace parts myself so it hasn't been that
expensive.

3 years ago the guy who tuned up the furnace put his meter on it and
said it was 85% efficient. [He retired and since then I've had
idiots do the furnace & I've re-done it after they left. But I'm
guessing it is still close. It sounds good & burns clean.]

I only burn 420-500 gallons of oil a year. At current prices that's
about $11-1300/yr. A high efficiency burner might save me 15% of
that- so say $200 a year. That's a 15+yr payback for a new
furnace-- so buying a new furnace now to save money isn't feasible.

I've considered buying a new gun or chassis, and see that they can be
had for about $300. On the surface that seems like cheap
insurance to just have one standing by. Unfortunately I don't see
any that match what I have.

The furnace is a Borg-Warner- U-447102
[also a # P2UFD17F0801A on it]
and the burner is a Ducane DMR-10A

It is rated for 85,000 BTU & I'd say from usage is about right-- on
the rare days when it hits 20 below zero it heats the house, but
doesn't shut down much.

Any thoughts?

thanks,
Jim