Upgrading a furnace or boiler from 56% to 90% efficiency in an average cold-climate house will save 1.5 tons of carbon dioxide emissions each year with gas fuel, or 2.5 tons with with oil fuel.
Heating and cooling account for about 56% of the energy use in a typical U.S. home, making it the largest energy expense for most households. A wide variety of technologies are available for heating and cooling your home, and they achieve a wide range of efficiencies. In addition, many heating and cooling systems have common supporting equipment, such as thermostats and ducts, which provide opportunities for more energy savings.
Understanding the Efficiency Rating of Furnaces and Boilers
Furnace and boiler efficiency is measured by annual fuel utilization efficiency (AFUE). The Federal Trade Commission requires new furnaces or boilers to display their AFUE so consumers can compare heating efficiencies of various models.
AFUE is the ratio of heat output of the furnace or boiler compared to the total energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the energy in the fuel becomes heat for the home and the other 10% escapes up the chimney and elsewhere. AFUE doesn’t include the heat losses of the duct system or piping, which can be as much as 35%.
You can identify and compare a system’s efficiency by not only its AFUE but also by its equipment features, listed below.
Old, low-efficiency heating systems:
- Natural draft that creates a flow of combustion gases
- Continuous pilot light
- Heavy heat exchanger
- 68%–72% AFUE
Mid-efficiency heating systems:
- Exhaust fan controls the flow of combustion air and combustion gases more precisely
- Electronic ignition (no pilot light)
- Compact size and lighter weight to reduce cycling losses
- Small-diameter flue pipe
- 80%–83% AFUE
High-efficiency heating systems:
- Condensing flue gases in a second heat exchanger for extra efficiency
- Sealed combustion
- 90%–97% AFUE
Retrofitting Your Furnace or Boiler
Furnaces and boilers can be retrofitted to increase their efficiency. These upgrades improve the safety and efficiency of otherwise sound, older systems. The costs of retrofits should be carefully weighed against the cost of a new boiler or furnace, especially if replacement is likely within a few years. If you choose to replace your gas heating system, you’ll have the opportunity to install equipment that incorporates the most energy-efficient heating technologies available.
Retrofitting options that can improve a system’s energy efficiency include installing programmable thermostats, upgrading ductwork in forced-air systems, and adding zone control for hot-water systems.
Replacing Your Furnace or Boiler
Energy efficiency upgrades and new high-efficiency heating system can cut fuel bills and pollution output in half. Modern conventional heating systems can achieve efficiencies as high as 97%, converting nearly all the fuel to useful heat for your home while older furnace and boiler systems have efficiencies in the range of 56%–70%. Upgrading a furnace or boiler from 56% to 90% efficiency in an average cold-climate house will save 1.5 tons of carbon dioxide emissions each year with gas fuel, or 2.5 tons with with oil fuel.