To calculate the energy-savings difference between two systems, divide the low efficiency by the high efficiency and subtract that figure from 1. In your case, the 80%-efficient furnace will reduce your current heating costs by 37% (1 - [.50/.80] = .37). The high efficiency system will cut your costs by 47% (1 - [.50/.94] = .47).

Now, let's say your current heating costs average $750 a year and installing a 94%-efficient furnace would cost you $500 more than installing an 80%-efficient model. The 94%-efficient furnace would save you 10% more a year in operating costs than the 80%-efficient model would (0.47 - 0.37 = 0.10). That's a $75 per year savings. Dividing the $500 installation price difference by the annual energy saving shows that you would receive a payback on your efficiency investment in about 6.7 years. Since a well-maintained gas furnace can generally be expected to last 15-20 years, you should have many years of savings to spend or reinvest after you achieve payback on your initial investment.

Of course, your real savings and payback rate will depend on the actual purchase and installation price of the systems you consider.

Before making a decision between a mid-efficiency and high-efficiency gas furnace, the CWLP Energy Experts would advise you to consider the wisdom of replacing your gas heating system with a new all-electric heat pump. With today's gas prices and the availability of CWLP's Heat Pump Rebate for qualifying installations, you might find a heat pump will be a more economical option than a gas furnace. For more information about heat pumps, contact the CWLP Energy Experts.