I understand that contemporary furnaces are much more energy efficient than older ones. The figures I've seen (from furnace salesmen, of course) says that today's are 95% efficient vs. 55% efficiency for those sold 12 years ago. I assume those numbers are in ergs per eep or something. I recently put in a low-water-useage toilet, and got a $100 rebate on my utility bill from the city, so it may be worth your while to investigate if something similar is offered where you are on furnaces. As Spaw says, best to do whatever you decide before it dies entirely, because it will be 2:00 on Saturday morning, with an outside temperature of -15, when it does. Try Consumer Reports for information on different types and brands.