Our Ratings Tables show how area heating and air-conditioning services were rated by their surveyed customers. Some companies were rated “superior” for “overall performance” by 90 percent or more of their surveyed customers. But some scored much lower, receiving such favorable ratings from only 60 percent or fewer of their surveyed customers.

We also found massive price differences. Although most consumers, surprisingly, don’t bother to get competitive bids even for costly jobs, obtaining multiple bids will save homeowners hundreds, or even thousands, of dollars.

If you need new equipment, get several companies to prepare written proposals. Carefully compare their proposed designs because the quality of the design might affect how quickly and uniformly your house is heated or cooled, how much energy it consumes, how much noise it makes, what drafts it produces, the amount of space the system occupies, maintenance, and other important aspects of performance.

Heating and air-conditioning services are likely to push for annual professional maintenance visits, and many will offer a maintenance contract. It is not clear that such frequent professional service is needed as long as you are diligent about the most important maintenance task: replacing air filters whenever they get dirty.

If you are considering buying new equipment, be skeptical about claims of cost savings from more energy-efficient equipment. There may be substantial savings—and there are compelling public-interest reasons to install efficient equipment—but some companies exaggerate the amount of savings in order to sell new, or more expensive, equipment. Get several companies to make proposals, ask for documentation of how much the new equipment will cut your energy bills, and ask questions.