What every best Furnaces has:
- The proper AFUE rating.
- Two stage valves.
- A programmable thermostat.
The major manufacturers of gas furnaces include Amana, American Standard, Bryant, Carrier, Goodman, Lennox, Rheem, Trane and York. All of these brands make multistage furnaces, and all make at least some models that have an AFUE of 90 percent or more. Most have fairly similar repair histories, with one notable exception.
In a 2014 survey conducted by ConsumerReports.org, based upon feedback from their subscribers, repair history was fairly consistent between all brands, except York, which had a much higher incidence of repairs than the other brands. American Standard has the best repair history, closely followed by Trane and Carrier.
Repair history is important because furnaces are expensive to repair; even more expensive to replace. However, you may be better off replacing your furnace if it's ailing and is more than 15 years old -- you're sure to save money in energy costs if you do so.
We did not find any surveys for oil furnaces, but the above manufacturers also make oil furnaces. Other top manufacturers of oil furnaces are Armstrong, Coleman, Ducane, Tempstar and Whirlpool.
Although there's little variation in overall quality between most furnace brands, specific models certainly do vary in terms of their features. Many older furnaces lack basic energy-saving features that are standard on newer models. For example, newer furnaces typically have vent dampers or an induced-draft fan to prevent heated air from escaping up the chimney when the heating system is turned off. Older furnaces that lack this feature are so inefficient that the American Council for an Energy-Efficient Economy (ACEEE) recommends replacing them. Also, many older furnaces have pilot lights that run continuously, ready to light the burners whenever the furnace turns on. Newer furnaces generally use electronic spark ignition, which strikes a spark to kindle a lame only when it is needed. An even newer method is hot-surface ignition, which uses a white-hot coil to ignite the gas. The advantage of that is that the ignition coil won't corrode or collect dirt or bugs the way a spark plug can. Another feature typical of new furnaces is multistage (or multispeed) operation, covered in our discussion of furnace efficiency.
Other new features are specific to certain furnace models. For example, every gas furnace includes a heat exchanger, the part of the furnace that extracts heat from the gas as it burns. Condensing furnaces, however, include a second heat exchanger, which recovers the heat from a furnace's exhaust gases. This process leaves behind cooled gas (which may be vented out through a wall with inexpensive PVC pipe, rather than sent up the flue) and water, which must be drained or pumped away. All furnaces with an AFUE of 90 percent or more are condensing furnaces. Because the exhaust gas may be corrosive, the second heat exchanger must be made of some material that will resist corrosion, such as stainless steel. The best heat exchangers will resist corrosion and chemical buildup during the entire life of the unit.
Another feature that experts recommend is sealed combustion. This seals the furnace's burner from household air, which provide protection from carbon monoxide escaping back into the home. A sealed-combustion furnace can improve efficiency as well.
The valves on a gas furnace may also effect its efficiency. Two-stage gas valves open up at full throttle when the furnace is first turned on, then cut back the flow of gas to save fuel. In addition to their energy-saving benefits, two-stage valves tend to be better built than standard gas valves, according to experts.
A final energy-saving feature that may be of interest is zoned heating. With this feature, you can send different amounts of heat to different rooms or areas in your home. Programmable furnace thermostats, combined with a central controller and a series of dampers to control airflow, adjust the amount of heat each room receives at different times of day. This feature can be very useful in larger homes, especially if different parts of the home have different heating or cooling needs (for example, because one area has many more windows, or for upstairs bedrooms that are primarily used at night). However, experts say zoned heating systems may require repairs more often. Zoned heating works best with a variable-output furnace.