I had an energy audit yesterday. The guy said that I should consider switching from oil (boiler) to propane, since propane is cheaper and there also is a $1500 rebate from the state. While we burn wood, it's probably good for 50% or so of our heating costs. The oil burner seems more finicky than the gas units I've had in the past - yearly checkups and he said it was burning dirty (high CO), so I have to call the oil guy, again - all of which costs money. Plus, there'd be an extra flue in the basement . Anyway, is there a general rule of thumb on switching, like if the price diff. is X then payback period would be Y? I'm going to start poking around to see if I can find anything. I think he said there's a unit, Triangle?, that's small enough to hang on a wall and provides instant hot water too.