Environmental

High Efficiency = EcoSmart Homes

Efficiency matters

The more efficient a furnace, obviously, the lower your energy bill for heating. Calculating a furnace's energy costs requires considering both the gas it burns and the electricity it consumes to run its blowers and controls.

How efficiently a furnace converts gas into heating energy is reflected in its annual fuel-utilization-efficiency (AFUE) rating, which is measured as a percentage. The higher that percentage, the more heat the furnace can wring from each therm of gas-and the lower the environmental impact of its emissions.

Furnaces have generally become more energy-efficient over the years. A typical gas furnace made in the early 1970s has an AFUE of about 65 percent. Today, the lowest efficiency allowed by law for new gas furnaces is 78 percent, and the most efficient models have an AFUE of about 97 percent-or near-total efficiency.

The price of a furnace generally rises in step with its fuel efficiency. A furnace with a 90 percent AFUE can cost about $1,000 more than a similarly sized unit with an 80 percent AFUE. However, that additional cost can generally be recouped in lower fuel bills over the lifetime of the furnace. Just how quickly the investment is recovered, though, depends on more than the difference in AFUE between the two units; the electrical bills to run two furnaces with different AFUEs can differ significantly. Payback times will also be affected by the climate where you live, how well your home retains heat, and the rates you pay for gas and electricity.

To help you decide on a level of efficiency for your new furnace, insist that the contractor select models in a range of efficiencies. Have the contractor calculate the annual estimated operating cost of each model you're considering, rather than simply estimate it. He can complete these calculations by plugging information on the unit's AFUE and electrical consumption, on local utility rates, and on characteristics of your home into one of several computer programs designed to make such estimates. Make sure the installation quotes also consider the cost of any changes to venting required by any appliances in the home.

Weigh the operating costs of the various furnaces against their price and features. Since more-efficient furnaces generate fewer emissions, environmental considerations may also weigh in your decision.

Given that most furnaces with an AFUE over 90 percent are quite expensive, they're likely to be economic only in regions where winters are especially harsh-including most of the Northeast and Midwest. Also, given the reliability indications for such models, it's wise to ask the contractor some additional questions about one you may be considering: Is the model fairly new (say, two years or less) and thus relatively untested? If it's an older model, has the contractor noticed any reliability problems with it?