PS, nice look, I like that skirtaround porch , its got a southern plantation look
We have a similar sitution on the main house (wrapround porch on 2 sides). We have a rolled seam metal roof (used to be 150 year old slate) . The "telescope additions that stick our of the sides without porches are separate wings with their own zones of heating. WE had used oil till last year when the oil guys dumped a load of fule into our basement by inattention (Gee I never knew yore tank could take 400 gallons).
The window replacements with the gas charged panes are great and 10 years later , no problems. IF anything happens, Pella will replace the whole section of window since they are double hung sashes.We dont notice any economies any more but when we replaced the windows 12 years ago (ALL 28 OF THEM) there was a huge difference just in the warmth in rooms (we have a stone house, on top of a barren windy hill surrounded by cornfields and woods). It used to blow air right through and the curtains would dance if it was a windy day.
We are now replacing my wifes studio windows within the next 2 weeks so, even though these leak air now, they wont soon. (When we built the studio addition it was chosen for its huge window design and at the time we could only get Delaware or Anderson (at that time Andersons were not a great quality window so we installed the Delaware windows knowing that theyd be replaced with something better in 20 years. Its been 15 and they are really leaking a lot.
Our fuel use is about 20% less now, mostly because of the tankless water heater (We had some problems at first with the installation). Now we can see the fuel usage drop even with the conversion of Btu values from oil to propane. That, coupled with the fact that propane is waay cheaper now.Propane is a fraction from natural gas as well as oil, and the fact that theres a whole big new gas strike in the US going on, Id really push for gas if your economy minded.
The conversions cost us about 18000 but with the tx credit and the savings we can repay us in about 3 years.