How do I calculate the cost of electricity and gas that's devoted to the heating and cooling of my house during the year? We have a gas furnace, but we use the same gas in our stoves and hot water heater. And I don't know how to calculate the electricity used specifically for the fan in our forced-air system and the compressor during the summer.

I'm curious about these numbers because I'd like to compare them to the cost of replacing components and/or making the house/HVAC system more efficient.

What advice do you folks have?