What the best furnace has

  • The proper AFUE rating. If you live in an area with harsh winters, you should recoup the additional expense of a high-efficiency condensing furnace (90 percent AFUE or more) over the unit's lifetime. However, if your winters are more temperate, and you live in a state where it's permitted, you may be better served with a furnace that has an AFUE of 80 percent. If you're unsure, have your contractor calculate fuel costs for both kinds of furnace, using your current bills; then you can tell if future fuel savings justify the additional $1,000 or more for a 90 percent AFUE furnace.
  • Two stage valves. These control the flow of fuel so that the furnace runs high when it's first turned on, then on a lower flow to maintain the temperature.
  • A programmable thermostat. These save energy by reducing the amount of work your furnace must do when no one's at home. For each degree you turn down the thermostat during an eight-hour period, you can reduce your heating bill by about 2 percent. Programmable thermostats can keep the house at a lower temperature when you're not home or at night. If you don't currently have a programmable thermostat, replacing your existing thermostat is a job most homeowners can do themselves, say experts.
  • Sealed combustion. This protects your home from carbon monoxide and is more energy efficient.
  • A long warranty. The warranty on your furnace will vary according to the manufacturer and the HVAC company and/or installer. More efficient (and expensive) furnaces tend to have longer warranties than basic models. With a condensing furnace, it is especially important to have a long-term warranty on the heat exchangers.

Know before you go

Repair or replace? Increased energy efficiency isn't always a good reason to replace a furnace that is still in good working order. Experts generally recommend replacing your old furnace if any of the following apply: it's more than 15 to 20 years old; it has a pilot light rather than electronic or hot-surface ignition; it does not have vent dampers or a draft fan; or it is a coal-burning model that has been converted to gas or oil.

Is your home energy efficient? Before you invest in a new heating system, experts advise improving the overall energy efficiency of your home through steps like adding insulation and sealing air leaks. This will reduce the heating load of your home, allowing you to purchase a smaller furnace. You may even find that you save as much as you would if you had purchased a more energy efficient furnace. Adding a variable-speed blower will also improve the efficiency of your heating system and reduce wear and tear because the furnace isn't always cycling on and off.

Do you have the right HVAC partner? It's important to take the time to find a good HVAC professional. The contractor should be licensed and insured, and the technician who installs the system should be certified by North American Technician Excellence (NATE). You should get at least three estimates in writing, and the contractor should base the estimate on a thorough survey of your home to calculate the size of the system you will need. Energy saving estimates should be done too, based upon your actual energy costs and recent bills.

Are you prepared to maintain your new furnace or boiler? Once your furnace or boiler has been installed, proper maintenance will keep it running at top efficiency. Steps to take include cleaning air registers and cleaning or replacing air filters in a forced air system, and cleaning baseboards and radiators, and periodically bleeding air, with hydronic systems. Your heating system should also be tuned up periodically: once a year for oil-fired furnaces and boilers, once every two years for gas-powered models. Experts say inadequate maintenance (or improper installation) accounts for twice as many furnace problems as defective equipment.

Elsewhere in this report:

Furnace Overview and Recommendations: Experts say that upgrading your old furnace to a new, high-efficiency furnace will lower your heating bills -- maybe by a lot. Editors discuss the types of furnaces and heating systems, as well as factors involved in choosing a new furnace.

Furnace Efficiency: A discussion of how furnace efficiency affects your wallet and the environment. Multi-stage verses single stage systems are explained.

Gas and Oil Furnaces: The two main fuel sources for furnaces are gas and oil. Editors explain the various merits of each type of fuel, and how the energy efficiency of any type of furnace be improved.

Boilers and Heat Pumps: Boilers and heat pumps provide heat differently than forced air furnaces and are growing in popularity. Radiant floor heating is also discussed.

Furnace Brands: Some furnace brands have better repair histories than others. Find out which company comes out on top. Furnace features within brands are also detailed.

Our Sources: These are the expert and user sources we consulted to give the most comprehensive overview of all types of home heating systems. They are listed in order from most helpful to least.

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