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? A good contractor has no problems with answering such questions or finding the answers for you.