How old is my "Air Conditioning" Furnasman Furnace? Model HG 100-27. The house was built in 1953, and this old aqua coloured baby looks very simple. I know it will need replacing at some point, but it keeps working. The utility company sent out a flyer saying heating costs typically account for up to 60% of household energy costs. My heating accounts for 58% of my costs. I use a programmable thermostat, so that helps. I can think of lots of things I need to spend money on (Replacing the leaking double glazed windows, and the fireplace dampers that are bent and don't seal off the heat loss)- should I really make replacing the old beast a priority?

Yes you should. The newer 95 to 98 % units really do save big bucks especially when you are replacing a 55 to 62% efficient older equipment.

Windows and fireplace dampers are also very important but you can caulk and use plastic inside storm windows for that and the dampers can be picked up at any brick supply yard. Just take your old damper out to find a replacement.

I agree with hvac1000. Look at it this way if you commuted to work 80 miles a day in a car that got 6 miles to the gallon would you buy a newer car that got 20 miles to the gallon to help save money. Buying the new unit will cost some money on the front end but it will pay for its self and save you money in the long run.