My folks gas bill (HUGE old two story house) was around $380-$450 a month. It had an older gas furnace in it.
This year he got a little out of the retirment fund, and bought a new furnace 6k out of pocket.
The old furnace was 65% efficient. You couldn't touch the exhaust it was way too hot. (lots of heat taken off out the chimmney). THe new furnace is 90 some thing % efficient. It doesn't have an exhaust pipe. It has an exhaust tube(plastic). No heat is being wasted by this guy.
He also got a new digital thermostat when they installed the new furnace. Together they save on average of $100-$150 a month.
Suggestions that make a huge difference.
Digital thermostat: It can turn down the heat when you leave for work, and turn it up 5 minutes before you get home. It can turn down the heat when you are asleep, and turn it back up rioght before you wake up. Estimate maybe 10-20% savings. You can pick em up from $50-$100 at any home store.
Plastic the windows:
My place here is cheap to heat, I use power. the bill without plastic on thw windows $140, bill with plastic $110
Foundation: Close the vents if it has any. If it is pourous, or not sealed well, plastic around it. Big difference.
Caulking: Anywhere you got a draft, of a wire/cable going through the wall, caulk the hell out of it. I'm a caluking nazi lol.
FSTBDY, you;re right your windows will kill ya. I would definetaly get some plastic up if you haven't already. Also check out the attic if havent already done that too. A good layer of blown in will really help up there.
I can just imagine without all the new siding and insulation you had done. I bet the bill bfore that was crazy scary.