Currently our furnace is in good shape, it was cleaned, inspected and had a year warranty slapped on it a short while back, it is nearly 20 years old so it will not last for ever but it is also a sealed combustion high efficiency model...
Punched our full utility bill in to an
online template that our utility has avalible and we use one third the fuel to heat our house of what other houses in our area that are of simaler size and age tend to use and last year were using 2/3 of the electricity, with how we've cut back that electrical usage should drop to 1/3 or less of what everyone else with a house our size and number of people.
The site also allows vague details about usage, so it's not comparing someone with central air to someone without, or a gas water heater to an electric.
It also gives rough prices and savings of different things, like heat pump units and it looked like the pay back would be 15-20 years, at that point I would just go with solar hot water as we have an ok lot for solar, we checked that out before buying the house.