Residential SW Washington

Technical tip: How to explain heating efficiency ratings

What’s your response when a customer asks: “How efficient is my heating system?” Methods of determining heating system efficiency vary by fuel source, and it helps to have a solid understanding of available rating systems.

Combustion heating systems These systems can be compared using the Annual Fuel Utilization Efficiency, AFUE, number, which factors in fuel combustion inefficiencies, exhaust flue heat loss and heat loss from the appliance itself. Check the yellow and black Energy Guide tag to see the AFUE of a particular model. Older combustion heating appliances may have AFUEs as low as 60 to 70 percent, while newer equipment AFUE numbers range from 80 to 98 percent.

Gas furnaces Many high-efficiency gas furnaces have electronically commutated motors, ECMs, which provide advantages over standard gas furnaces, including reduced noise, better air flow control and lower energy use. A furnace fan without an ECM may use in excess of 500 kilowatt hours per year, while a furnace fan with an ECM may use as few as 200 kWh per year.

AFUE ratings can be found at the Air-Conditioning, Heating and Refrigeration Institute’s website.

Electric heat pumps There are four rating numbers for heat pumps: the Heating Season Performance Factor, HSPF; the Seasonal Energy Efficiency Ratio, SEER; the Energy Efficiency Ratio, EER; and the Coefficient of Performance, COP.  The higher the rating number, the more energy efficient the heat pump.

HSPF measures how efficiently a heat pump provides heat. All heat pumps operate at greater than 100 percent efficiency: one BTU of input to the appliance produces more than one BTU of output. In contrast, electric-resistance heating systems, such as electric furnaces, baseboard heaters, wall heaters or radiant floors, operate at or about 100 percent efficiency where one BTU of input roughly equals one BTU of output. This is also known as the Coefficient of Performance, COP. A heat pump may have a COP of 1.5 to 4.0, meaning it operates at 1.5 to four times the efficiency of electric-resistance heat. A heat pump operates at this efficiency because it uses a compressor and refrigerant to move heat from one space to another, instead of generating heat. The HSPF records the number of BTUs of heat delivered per each watt-hour of electricity used, and it factors in both the high-efficiency compressor and the less efficient electric resistance backups.

SEER and EER are ratings of the heat pump’s air conditioning capability, for seasonal performance and under set conditions, respectively. SEER and EER are similar to HSPF in that they compare the number of BTUs of heat removed per each watt-hour of electricity used.

For a heat pump to reach its promised rating, a proper manufacturer-specified refrigerant charge is vital. An incorrect refrigerant charge prevents the compressor from properly heating or cooling a home’s living space, and is one of the most common reasons for lackluster heat pump performance. Energy Trust recommends commissioning all new heat pumps to ensure that customers receive the full benefit of their investment in cost and energy savings.