Gas Furnace Buying Guide

How do most people go about buying a furnace? First, they call contractors and ask for estimates. To prepare this report, we did too. More than 500 specialists in residential heating and air conditioning told us about their experiences installing and maintaining heating equipment.

Size Matters
The furnace’s specifications should fit your needs. A furnace that’s too small won’t keep your house comfortable during extremely cold weather.

Partly to avoid that possibility, the furnaces in most homes are larger than necessary. Initial cost is only one of the drawbacks of that strategy. A furnace that’s too large will cycle on and off more frequently. That puts more wear on its components, wastes energy, and might cause the temperature to vary uncomfortably. Also, a larger replacement furnace might require larger ducts. If ducts aren’t the right size, airflow can be noisy.

To be sure of correct sizing and a proper installation, choose a reputable contractor who will take the time to calculate your heating needs according to an industry standard such as the Manual J HVAC residential load calculation from the Air Conditioning Contractors of America. Such calculations take into account the climate and the size, design, and construction of your house. Once the furnace is installed, maintain it regularly according to the manufacturer’s recommendations. Our survey helped to confirm this advice. When we asked about the most common reasons for service calls for furnaces, contractors cited human error, inadequate maintenance, or improper installation twice as often as defective equipment. See our full report on the most and least reliable gas furnace brands.

Efficiency Also Matters
Most new central heating systems use gas, the most common heating fuel. How efficiently a furnace converts gas into heating energy is reflected in its annual fuel-utilization-efficiency (AFUE) rating, which is measured as a percentage. The higher the number, the more heat the furnace can wring from each therm of gas. Because efficient furnaces generate fewer emissions, environmental considerations might also influence your decision.

Furnaces have become more energy-efficient over the years. A gas furnace made in the early 1970s typically has an AFUE rating of about 65 percent. The lowest efficiency allowed by law for new gas furnaces is 78 percent, and some new models achieve 97 percent, near-total efficiency.

The price of a furnace generally rises in step with its fuel efficiency. A furnace with a 90 percent AFUE rating might cost $1,000 more than a similarly sized unit with an 80 percent rating. But you can often recoup that additional cost through lower fuel bills over the life of the furnace, especially in regions such as the Northeast and Midwest, where winters can be harsh. How quickly you recover the investment depends on more than just AFUE. The electricity to run furnaces with different AFUE ratings can vary significantly. The climate where you live, how well your home is insulated, and your local gas and electricity rates also affect payback times.

As you decide, insist that the contractor select models in a range of efficiencies, and calculate the annual estimated operating cost of each model you’re considering by plugging information on each unit’s AFUE rating and electrical consumption, local utility rates, and characteristics of your home into one of several computer programs designed to easily calculate estimates. Make sure that the quotes also include the cost of any changes to venting required by any appliances in the home.

Other questions to ask the contractor: Is the model you’re considering fairly new—introduced, say, within the past two years—and thus relatively untested? If it’s an older model, has the contractor noticed any reliability problems with it?

You can make your home more energy-efficient in several ways. Turn down the thermostat in winter; just 2° F cooler will save you money and reduce emissions by about 6 percent. You might not even feel the difference, especially at night or when you’re out of the house—a programmable or smart thermostat can help here, and you should read our guide to smart thermostats and our guide on using smart devices so that you’re not spending money heating your entire home when some rooms are empty. Draw the curtains at night to block the chill from a cold window.

More old-school advice: Keep the windows covered on sunny days during the summer, and uncover them on sunny days during the winter to benefit from some free solar heating. Reduce heat loss from ducts by sealing leaks and, where feasible, insulating ducts.

Repair or Replace?
If your gas furnace falters or fails, a few simple procedures may save you the cost and trouble of seeking professional help.

• If you’re getting low airflow, check the air filter on the furnace; a clogged filter could cut airflow to a trickle.
• See whether there are loose wires or a malfunction in the thermostat. For an electronic thermostat that runs on batteries, try changing them.
• Are fuses burned out or circuit breakers tripped? If so, power may have been cut to the fan or circuit board.

If those steps don’t work, call a heating contractor. Despite the improved efficiency of most new furnaces, it’s generally more cost-effective to repair a furnace than to replace it. However, if a key component, such as the heat exchanger or control module, fails, you’re probably better off replacing the furnace, especially if the unit is more than about 15 years old. Furnaces typically last an average of 15 to 20 years.

Most and Least Reliable
If you have to replace your furnace, you’ll be happy to hear that today’s gas furnaces are more energy-efficient, resulting in substantial fuel savings. On average, around a quarter of gas furnaces are likely to experience a break by the end of the 10th year of ownership. This, however, varies considerably by brand. That’s what we found based on information from our members. In our most recent surveys they reported on their experiences with 36,348 gas furnaces installed new between 2005 and 2021.

Of the more than 20 gas furnace brands we rated, Trane and Payne stood out as the most reliable, earning Excellent ratings for predicted reliability. Six other brands earned Very Good reliability ratings.

Each brand of furnace offers a similar array of key features, depending on price. The furnace features most often highlighted in product literature and sales pitches are generally the ones found on the higher-efficiency models, but some manufacturers also offer them on premium versions of low-efficiency furnaces.

Variable-Speed Blowers
These can deliver air slower, while often making less noise, when less heat is needed. That produces fewer drafts and uncomfortable swings in temperature.

Variable Heat Output
Available on some furnaces that have a variable-speed blower, this feature can increase efficiency and comfort by automatically varying the amount of heat the furnace delivers, usually between two levels. The furnace can thus deliver heat more continuously than one with a fixed heat output.

Air Filtration
Fitting a furnace with an electrostatic filter, which uses an electrical charge to help trap particles, or a HEPA filter can reduce the amount of dust blown through the heating system. That might help people with asthma or other chronic lung diseases, as well as allergies, and you should read more about indoor air quality and our air purifier tests if this is a concern.

Dual Heat Exchanger
Heat exchangers are the components that draw heat from the burned gas. To draw more heat from the air they burn, energy-efficient furnaces supplement the primary exchanger with a second exchanger. Because the exhaust gases in that second exchanger might yield a corrosive acidic condensate, the second exchanger is made of stainless steel, lined with plastic, or otherwise protected.

Ignition System
Fewer and fewer furnaces have a pilot light—a flame that burns continuously, awaiting the next command to ignite the burners. Furnaces with intermittent, direct spark, or hot-surface ignition do away with the constant pilot light in various ways. That increases efficiency and is usually reflected in a furnace’s higher AFUE rating.

Zoned Heating
This feature uses a number of thermostats, a sophisticated central controller, and a series of dampers that control airflow to deliver different amounts of heating or cooling to different parts of the home. The larger the home, as a rule, the more useful zoning is. That’s especially true if sections of the home have different heating or cooling requirements, because of wide variations in the number or type of windows, for example. But contractors we interviewed said that furnaces connected to zoned ductwork generally require more repair.

Warranty
Basic, usually low-efficiency, furnaces often have a shorter warranty than their premium counterparts.

To heat your home and water, you can choose from among several energy sources. But gas is currently the most common heating fuel—most new central heating systems use it.

Heat Pumps
Heat pumps that wring heat from outdoor air (and reverse the process in summer to act as an air conditioner) are inexpensive to install as an alternative to a cooling-only air-conditioning system. That makes them the preferred way to heat in regions where winters are typically short and mild. (Our guide to heat pumps will give you a good overview.)

Other inexpensive electric-heat options include strip heaters, which are installed in the ductwork of central air conditioning, and permanently installed baseboard units in each room. But before you consider any type of electric central heating in colder regions, keep in mind that electricity rates are much higher than those for natural gas and are likely to remain that way for the foreseeable future. You can get rate information for various fuels from local utilities and suppliers.

Oil Furnaces
These venerable models still retain a niche in older homes, mostly in the Northeast.