Understanding Efficiency Ratings
By Chris Dorsi
If you have an older forced air furnace, you may be able to save energy and money by replacing it with a more efficient system. The best new furnaces consume up to 30 percent less fuel than older systems.
The efficiency of combustion heating systems such as furnaces is measured in Annual Fuel Utilization Efficiency (AFUE). This rating is included on the yellow Energy Guide label posted on all new appliances, and it measures the efficiency at which the appliance delivers heat to your home's ductwork. Many older furnaces have an AFUE of about 60 to 70 percent. This means that at least 30 percent of the fuel you purchase is wasted as heat that escapes up the chimney or out the sides of the furnace.
You can identify these old-fashioned conventional furnaces by their standing pilot light (a small visible flame that lights the main burners), and open draft diverter (that allows room air to flow into the chimney). When you shop for a new gas furnace, you'll have two choices of efficiency:
T Mid-efficiency furnaces have an AFUE rating of 80 to 82 percent. This efficiency upgrade includes an electronic ignition (no pilot light), a lightweight heat exchanger (less warm-up time), and a fan that controls chimney draft (less heat going up the chimney).
T High-efficiency furnaces have an AFUE of 90 percent or higher. Like the AFUE 80+ furnace, these furnaces have electronic ignition and a draft fan. The AFUE 90+ furnaces will also have a sealed combustion chamber, offering an important safety advantage since they draw combustion air from outdoors. Finally, the AFUE 90+ furnaces extract extra heat from their combustion gases by cooling them to the point of condensation, releasing latent heat.
No one looks forward to the day their furnace needs to be replaced. But the new generation of heating equipment can save you a lot of energy and money in the long run.