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Efficiency Ratings: AFUE, COP, HSPF, SEER & EER
Take a few moments to familiarize yourself with the efficiency ratings you’ll find on various pieces of equipment.
Boilers and Furnaces
Rating to look for: AFUE
The annual fuel utilization efficiency (AFUE) of furnaces and boilers measures their performance over a typical heating season. It takes into account things like on-and-off cycles and heat loss through the chimney or vent, and is the most useful furnace and boiler rating available. The higher the rating, the more efficient the unit.
There is a second efficiency rating for furnaces and boilers and it is known as steady-state efficiency. It is higher than an AFUE rating but it’s not as helpful. It measures the equipment’s performance after it has been running a short while and all components have reached their normal operating temperature. The steady state efficiency of furnaces and boilers is determined by
comparing the amount of heat that’s available in the fuel to the amount that is converted into usable heat, but it does not include off-cycle losses.
Advanced equipment which is certified as meeting the EPA or CSA-B415 emissions standard normally exceeds 60% and averages 70% efficiency. Conventional wood-burning appliances which are not certified as low emission average 50% efficiency, with a range of 35 – 70%. Although some wood burning equipment is specifically certified for efficiency, most is not.
Also, most wood-burning appliances are manually operated, not automatic, and so the practices of the operator will affect the efficiency actually achieved.
Ratings to look for: COP, HSPF
Earth energy systems are rated for heating efficiency by comparing them to electric resistance heat. The measurement used is called the coefficient of performance – COP – and is determined by dividing the heat output by the energy input. Since the COP of an electric resistance heater is 1.0 – which means that the same amount of energy that goes into it as electricity comes out as heat – any rating higher than 1.0 means that for the same amount of electricity going in, more heat comes out. Look for a COP of 3.1 or more.
The heating efficiency rating for an air source heat pump is called the heating seasonal performance factor (HSPF). This is determined by dividing the total heat provided during the season (in BTU) by the total energy consumed by the system (in watt-hours). The higher the rating, the more efficient the heat pump is over the entire heating season. Look for an HSPF of more than 5.9.
Air conditioners and air source heat pumps
Ratings to look for: SEER
A SEER rating, which stands for Seasonal Energy Efficiency Ratio, tells you the cooling energy efficiency of air conditioners and air source heat pumps. The rating is determined by dividing the total cooling provided during the season (in BTU) by the total energy consumed by the system (in watt-hours). The higher the rating, the more energy-efficient the unit. SEERs for new central air conditioners and air source heat pumps currently range from 10 to 17. For room air conditioners, the range is 8 to 12.
Earth energy systems
Ratings to look for: EER
If you want to know how efficiently an earth energy system can cool, look for the letters EER, which stand for energy efficiency ratio. EER ratings are determined by dividing the cooling output of the ground or water source heat pump (in BTU/hour) by the power input (in watts). Look for an EER of at least 10.5.
Hot water equipment
Storage-type Hot Water Heaters
An energy factor (EF) is used to rate the energy efficiency of storage-type hot water heaters. Both on-cycle efficiency and off-cycle losses are taken into account, which makes it a seasonal rating. The higher the EF, the more efficient the unit. You can expect the following energy factor ranges for new storage-type water heaters:
- Gas 0.56 to 0.86
- Electric 0.87 to 0.98
- Oil 0.53 to .68
A storage-type water heater added to an earth energy system will normally have an energy factor of 2.7 to 3.1.