How to Buy an Energy-Efficient Gas Furnace
Information about energy-efficient gas furnaces in this section includes the following:
| Efficiency Recommendation Cost-Effectiveness Example How to Select Condensing Furnaces |
 |
Sizing Duct Sealing User Tips For More Information |
Also provided is a portable document format version of How to Buy an Energy-Efficient Gas Furnace (PDF 68 KB, 2 pp). Download Adobe Reader.
| Efficiency Recommendation | ||||
|---|---|---|---|---|
| Product Type | Recommended AFUEa,b | Best Available AFUE | ||
| Residential Gas Furnacec | 90% or more | 97% | ||
a AFUE (annual fuel utilization efficiency) is a measure of heating efficiency on an annual basis. The DOE test procedure defines AFUE as the heat transferred to the conditioned space divided by the fuel energy supplied.
b Based on DOE test procedure, see 10 CFR, Sub-Part B, Appendix N.
c Residential gas furnaces include those fired by natural or propane gas, with input ratings less than 225,000 Btu/hour.
| Cost-Effectiveness Example | ||||
|---|---|---|---|---|
| Performance | Base Modela | Recommended Level | Best Available | |
| AFUE | 78% | 90% | 97% | |
| Annual Energy Use | 790 therms | 685 therms | 635 therms | |
| Annual Energy Cost | $320 | $270 | $250 | |
| Lifetime Energy Costb | $4,600 | $4,000 | $3,700 | |
| Lifetime Energy Cost Savings | — | $600 | $900 | |
a The efficiency (AFUE) of the base model is just sufficient to meet current U.S. DOE national appliance standards.
b Lifetime energy cost is the sum of the discounted value of annual energy costs based on average usage and an assumed furnace life of 20 years. Future gas price trends and a discount rate of 3.4% are based on federal guidelines (effective from April 2000 to March 2001).
Cost-Effectiveness Assumptions: Annual energy use calculation is based on the standard DOE test procedure. Furnace model: heating capacity of 70,000 Btu/hr. Usage assumption: 2,080 heating load hours per year. Assumed gas price: $0.40/therm, the Federal average gas price in the U.S.
How to Select an Energy-Efficient Residential Furnace
For furnaces purchased through commercial sources (retailer or distributor), look for the EPA/DOE ENERGY STAR® label; all ENERGY STAR® models meet this efficiency recommendation. Visit the ENERGY STAR® Web site for a list of complying models. Alternatively, look at the yellow "EnergyGuide" label to identify models with an AFUE that meets the Recommendation.
For a contractor-supplied gas furnace, specify an ENERGY STAR® qualified model, or one with an SEER that meets the recommended level.
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. The required furnace capacity should be determined based on the referenced ACCA calculation procedure (see For More Information).
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 set-back thermostat to minimize unnecessary operation of the unit.
For More Information
- Environmental Protection Agency has ENERGY STAR® furnace listings, which includes a list of models that comply with this Recommendation.
Phone: (888) 782-7937 - American Council for an Energy-Efficient Economy (ACEEE) publishes the Consumer Guide to Home Energy Savings.
Phone: (202) 429-0063 - Air Conditioning Contractors of America (ACCA) publishes Manual J, a load calculation guide for residential heating and air conditioning, and Manual S, a sizing guide for heating and cooling equipment.
Phone: (202) 483-9370. - Home Energy Magazine provides energy conservation tips.
Phone: (510) 524-5405 - Gas Appliances Manufacturers Association (GAMA) publishes Consumers' Directory of Certified Efficiency Ratings.
Phone: (703) 525-9565 - Lawrence Berkeley National Laboratory provided supporting analysis for this recommendation.
Phone: (202) 646-7950