January 2007
Time for a Change?

When and Why to Replace Your Gas Furnace

Most homes in the United States are heated with furnaces, and heating your home can account for up to two thirds of your energy bill. So how do you know if your gas furnace is doing all it can to provide you with the most efficiency, and how do you know when it's time for a change?

Is your furnace functioning like it should be? It may be time for a new one.

There are several reasons that you might want to replace your gas furnace: because it is old, worn out, inefficient or just too large for your needs. While replacing your furnace can be costly—at least $2,500 to $3,000 for the unit and installation—it can also save you big bucks in the long run.

Is Your Furnace Too Old?

On average, heating systems last about 25 years with proper maintenance. That number, however, can vary, and a qualified Heating, Ventilation and Air Conditioning (HVAC) contractor will be able to tell you whether or not it's time to replace it.

Furnaces with pilot lights or without induced draft fans may need to be replaced. Newer models are more compact, lightweight and energy efficient.

Is It Inefficient?

Even if your furnace hasn't reached its 25th birthday, it may not be functioning as well as it could be. Inefficient furnaces can be bad news for the environment and your wallet. In fact, the energy cost of an inefficient furnace can be nearly double that of an efficient one.

Older furnaces, especially those made before 1992 (when federal minimum efficiency standards were put in place), have a low annual fuel utilization efficiency (AFUE). The AFUE tells you how much energy is being converted to heat. For instance, if your gas furnace has an AFUE of 65 percent, that means that 65 percent of the gas used by the furnace warms your home, and the other 35 percent escapes as exhaust. The Federal Trade Commission requires that new furnaces display their AFUE, but if you do not know the AFUE of your furnace, a qualified HVAC contractor can determine this for you.

Older gas furnaces with pilot lights generally have AFUE ratings of 55 to 65 percent. New furnaces utilize electronic ignition rather than pilot lights. They are required to have an AFUE of at least 78 percent, but most models exceed 80 percent. The highest rated models have an AFUE of 97 percent, losing just three percent to exhaust. Furnaces with the ENERGY STAR distinction have an AFUE of 90 percent or greater.

Is Your Furnace Too Large?

Most homes have units that are larger than necessary. Furnaces that are too large operate less efficiently than properly sized furnaces because they cycle more often. They are also more expensive up front.

If you decide to put a new furnace in your home, don't just replace it with a furnace of the same size. If you have replaced windows or doors that provide less heat loss and leakage, your home will require less heating capacity. Have an HVAC contractor perform a better heat loss analysis of your home before you decide what size furnace you will need.

Even newly installed furnaces can be oversized, but they can sometimes be adjusted to lower their capacity to fit your home.

Ready to Buy? Here's what to remember:

  1. Take a look at the most energy efficient models (those with the ENERGY STAR label) and determine if they fit your needs. The higher efficiency models may cost more up front, but could save you money in the long run.
  2. Make your home as energy efficient as possible before you purchase a new furnace. Seal duct leaks, insulate ducts, replace weather stripping, add insulation and make additional improvements for optimum energy efficiency. Making these changes first will ensure that you get a unit that provides the correct heating capacity.
  3. Get a reliable HVAC contractor to identify and install the correct furnace for your home. Check out the HVAC Contractors Checklist for tips on finding a qualified person.

No matter the age of your furnace, proper maintenance, like changing the filter, is a must. An HVAC contractor should check your furnace twice a year—spring and fall—to ensure it is in good working condition.

Find the Right Person for the Job

HVAC Contractors Checklist

  1. Does the contractor hold the necessary licenses?
  2. Does the contractor have references?
  3. Was the contractor trained by the manufacturer of the furnace or by a technical school?
  4. Will the company service the furnace that they sell you?
  5. Does the contractor belong to professional organizations like the ACCA or RSES?
  6. Does the company have insurance?
  7. When the contractor comes to your home, does he/she perform calculations specific to your home?
  8. Does the contractor take time to answer your questions and explain your options thoroughly?

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