Reviewed and Revised on 10/15/2013
The following terminology can help one understand the energy efficiency of common Home Heating Systems.
Annual Fuel Utilization Efficiency (AFUE)
The efficiency of a gas (natural or propane) or oil furnace or boiler is measured in terms of its Annual Fuel Utilization Efficiency (AFUE), which describes the heat produced from the energy used. This rating takes into consideration various losses that may be involved such as from pilot lights, heat out of the exhaust stack, start-up, and stopping. AS As an example, a furnace with an AFUE rating of 80 converts 80% of the fuel it burns into usable heat. New furnaces usually rate in the mid 70s to low 80s for non-condensing furnaces and low to mid 90s for condensing furnaces, whereas older furnaces will be in the 50s or 60s. ENERGY STAR ® qualified oil and gas furnaces have annual fuel utilization efficiency (AFUE) ratings of 85% and 90%, or higher, making them up to 15% more efficient than standard models. Keep in mind, however, the AFUE does not consider the unit’s electricity use for fans and blowers.
Heating Season Performance Factor
The Heating Season Performance Factor (HSPF) applies only to heat pumps. HSPF is the ratio of heat provided in Btu (British thermal unit) per hour to watts of electricity used. This factor considers the losses when the equipment starts up and stops, as well as the energy lost during the defrost cycles. The higher the HSPF, the higher the efficiency of the unit.
Typical values for the HSPF are 6.8 for standard efficiency, 7.2 for medium efficiency, and 8 for high efficiency. Variable speed heat pumps have HSPF ratings as high as 9, and geothermal heat pumps have HSPFs over 10. The higher the rating, the more efficient the heat pump. ENERGY STAR qualified heat pumps have a higher seasonal energy efficiency ratio (SEER) and HSPF than standard models, which makes them about 20% more efficient than standard new models. The HSPF averages the performance of heating equipment for a typical winter in the United States, so the actual efficiency will vary in different climates.
Coefficient of Performance
The Coefficient of Performance (COP) is an older standard used prior to HSPF to measure the efficiency of heating systems. However, the COP is still used to measure the energy efficiency of geothermal heat pumps in the heating mode. By definition, all electric resistance space heaters have a COP rating of 1 (generally considered the most expensive method of heating). A unit with a rating of 3 means that the unit is 3 times more energy efficient than electric resistance heating.
Another important question to understand for Home Heating Systems is if the fuel type being used by the systems can make a difference in the home energy costs?
The answer to this is Yes! Homeowners must make it a point to check with their local utility before replacing an existing system. Many utilities have an entire department dedicated to energy conservation and/ or efficiency. They can advise not only on the types of fuel available in your particular location, but also on new technologies that make the most of the fuels available to you.
Keep in mind that fuels are measured and sold in different units such as gallons of oil, therms of natural gas, or kilowatt hours (kWh) of electricity, so comparing the price of dissimilar units is not useful. A more useful comparison is the fuel cost per amount of heat produced.
The Energy Information Administration’s Heating Fuel Comparison Calculator helps you make this comparison by factoring in the relative price based on the fuel heat content and the efficiency of the heating appliance. The site provides step-by-step instructions, including how to find cost and efficiency data to use with the calculator. In choosing a heating system, don’t rely solely on cost as many factors will determine the best heating system for your needs. To help you choose a heating system, the site also provides numerous links to additional information.