Although older furnaces and boilers had efficiencies in the range of 60% to 70%, modern heating systems can achieve efficiencies as high as 97%, converting nearly all the fuel to useful heat for the home. When selecting an efficient pulse-fired gas furnace, look for the ENERGY STAR® logo. The EPA estimates that ENERGY STAR® labeled heating and cooling equipment, when properly sized and installed, can save consumers 10% to 40% on heating and cooling bills. ENERGY STAR® furnaces are highly efficient, use less energy than conventional systems, and help reduce pollution associated with energy use.

Condensing Furnaces All models that meet the recommended levels are "condensing" furnaces. This technology takes advantage of normally exhausted heat in the furnace's flue gas. Condensing furnaces require slight modifications in installation and usually are considerably more expensive than standard efficiency models; consult the cost-effectiveness information to help determine the range of price premium that is justified for your location and fuel price.

Sizing
Oversizing of furnaces, besides raising purchase cost, will result in weaker energy efficiency due to excessive on-off cycling.

Duct Sealing
Average U.S. homes lose more than a quarter of their heating energy through leaky ductwork. Poor sealing of ducts can also generate comfort problems and, in some cases, cause backdrafting of gas-fired equipment (furnaces and water heaters). Ductwork should be inspected and sealed in conjunction with furnace installation.

User Tips
Consider leaving your furnace off during unoccupied hours or using a setback thermostat to minimize unnecessary operation of the unit.

Efficiency Recommendation

Non-Energy Benefits of ENERGY STAR® Gas Furnaces
ENERGY STAR® gas-fired furnaces make your home more comfortable. Some models are less prone to causing indoor air quality problems or house fires.

ENERGY STAR® gas-fired furnaces may provide the following benefits in addition to reducing your energy bills.

• Improved Comfort—Efficient furnaces provide greater comfort because they cycle on and off less often, and have improved controls so as to provide desired temperatures throughout the home.
• Improved Indoor Air Quality-Some efficient furnaces (e.g. sealed combustion units) contain and exhaust all the "combustion products" with no chance of their being introduced into the home.
• Improved Fire Safety-Efficient furnaces don't need to operate for as many hours to provide the required heat. This means that time when flames are present is reduced, which has been noted by some insurance companies as a benefit in terms of improved fire safety.

You can obtain additional benefits by having your contractor install the correct size (capacity) of furnace for your home. A properly sized furnace can reduce noise (because of its reduced airflow), increase comfort (because the longer run times provide a more consistent furnace output rate), improve combustion safety (because of decreased potential for depressurization), and also reduce energy consumption.

Sources: DOE, FEMP How to Select an Energy-Efficient Residential Gas Furnace, Lawrence Berkley National Laboratory Non-Energy Benefits of ENERGY STAR® Gas Furnaces, Photo: Heil Heating and Cooling Products