- AFUE - Annual Fuel Utilization Efficiency. The efficiency of a gas furnace or water heater is a measure of the amount of useful heat output to the amount of fuel input in Btus. If a furnace is rated at 80% AFUE then 80% of the energy input is turned into heat for the home and the other 20% is lost through the process of combustion. A 90% efficient furnace would only lose 10% due to combustion. The California Energy Code requires a minimum AFUE of 80%. Most modern high efficiency furnaces are rated at 92-96%. To qualify for federal tax credits equipment must be rated at 95 AFUE for natural gas and 90 AFUE for propane.
- SEER - Seasonal Energy Efficiency Ratio. The efficiency of an air conditioner measured in Btus of cooling output per watt-hours of electrical input. Many old A/C units are rated at 6-9. California code requires a minimum of 13.0 SEER. To qualify for federal tax credits equipment must be rated at 16.0 SEER.
- EER - Energy Efficiency Ratio. Similar to SEER but measured under hotter outdoor conditions. EER ratings normally apply to room air conditioners and ground source heat pumps. To qualify for federal tax credits equipment must be rated at a minimum of 12.0-13.0 EER for A/C equipment and 14.1-16.2 EER for ground source heat pumps depending on type.
- HSPF - Heating System Performance Factor. A rating of air source heat pump performance. Like SEER and EER it measures cooling output in Btus per watt-hour of electricity input. To qualify for federal tax credits equipment must be rated at a minimum of 8.5 HSPF for split systems and 8.0 for package units.
- COP - Coefficient of Performance. An older way of rating heat pump performance. A COP of 2.0 means the unit is performing at 200% efficiency, a COP of 3.0 would be 300% efficient.
- Energy Factor - The energy efficiency of a storage water heater based on the assumed use of 64 gallons of hot water per day, regardless of tank size. Newer conventional gas water heaters have an Energy Factor of 0.65 and above with condensing water heaters as high as 0.86. To qualify for federal tax credits a water heater must have an Energy Factor of at least 0.82.
- Thermal Efficiency - Like most of the other rating categories, thermal efficiency is a ratio of useable heat energy output to energy input often applied to high efficiency water heaters. To qualify for federal tax credits a water heater must be rated at a minimum of 90% thermal efficiency.
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