Windows are generally regarded to have among the longest payback
times, so they may not be the place to start.

More attic insulation is a huge bang for the buck though. I'd start
there.

Windows, however do provide a great deal of comfort in stopping drafts
and making things feel a lot better. If you don't have the reserve
now, consider plastic window film. The 3m window kits are actually
wonderful, and once treated with the blow dryer, they almost
disappear. For windows that spend most of the winter behind curtains
anyway, all the better. The 3m tape is where it's at--if you buy
bargain windows kits, you may regret it.

But if you can afford to do windows, do. They should payback in 20
years unless you go nuts with the top of the line windows.

Heating ... what do you have now?


HVAC is original late 1970 vintage, amazingly both air and heat still works
though not very efficiently. Heating is central natural gas fired units, one
for downstairs and one for upstairs. House about 3,000sf and I'm the only
one in it most of the time while wife out shopping so no need to fired up
the unit(s) just for one person.

--
Todd H.
http://toddh.net/