Maintaining a gas boiler.

Photograph by Nomad_Soul/Shutterstock

By Tanya Snyder

for National Geographic

Shopping Tips

The best way to save energy in your home is to make sure you have an efficient furnace. Heating accounts for up to half of the average household energy bill in colder parts of the country. By retrofitting your furnace for maximum efficiency, or buying a new furnace if needed, you’ll get more bang for your buck than you might expect.

Before you buy a big heating appliance, make sure you’ve done all you can to insulate your home. It doesn’t make sense to buy a state-of-the-art heating unit if all that heat is going to drift outside. First try adding a heat pump, sealing your ducts, or implementing any of the other Usage Tips listed here. You might be able to make your old furnace a lean, green machine.

Tried all that and you’re still ready to buy a new heating system? Let’s get to it. You have a lot to choose from. Let’s start with the basic breakdown:

  • Furnaces vs. Boilers: Furnaces circulate warm air to heat the home, and boilers use warm water. Boilers usually use radiators to distribute the heat, while furnaces use ducts. You can get a gas- or oil-burning model of either.

  • Condensing Furnaces: The most efficient furnace OR boiler you can get would be a condensing one. A condensing furnace (or boiler) captures the heat in the exhaust and, rather than sending it up the chimney to be wasted, uses that heat to turn water into steam. The furnace then takes the heat from the steam, condensing it back into water. These models are especially good for people living in cold climates. They cost more to install and maintain, but the fuel savings add up, both ecologically and economically.

  • Heat Pumps: People living in warmer climates might consider a heat pump. Both ground-source and air-source heat pumps are available. They work like an air conditioner that heats as well as cools. Heat pumps are extremely energy-efficient, especially ground-source pumps, because “temperatures underground are nearly constant year-round—warmer than the outside air during the winter and cooler than the outside air during the summer,” according to the American Council for an Energy-Efficient Economy (ACEEE). Heat pumps are expensive to install but they’ll save you a bundle on your energy bill. If you live in a cold climate, however, a heat pump isn’t for you.

  • Dual Use: A boiler used for hot water and home heat gives you two large appliances for the price of one. But ACEEE’s Jennifer Amann cautions against overestimating the energy savings. “Basically you’re firing up a huge boiler, even in the summer months, just to get a little bit of domestic hot water,” she says. But there are some new systems on the market she does recommend. “They use different types of controls to balance the load between water heating and space conditioning, and can operate very effectively at a lower demand during the summer months, just to supply hot water. They can be very effective.”

  • All-Electric Furnaces and Boilers: These lose no heat through the chimney, but the high cost of electricity in most parts of the country makes them a costly choice. Solar furnaces are being developed, but Amann says they still have some performance issues: “their savings and benefits have yet to be proven.”

  • Size Matters: Before you choose a furnace, have a contractor come to your house to help you figure out what kind to get for maximum efficiency. Don’t let a contractor install one that’s the same size as the old one without doing a full assessment. Most old furnaces are oversized, and consume more energy than necessary. Get one that’s the right size for your household and the right efficiency for your climate, and be sure it uses the right kind of fuel for your part of the country. And be sure to take into consideration any efficiency improvements you’ve already made to your house.

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