Reading efficiency ratings
Start with the equipment type, then compare the same rating and the complete configuration.
SEER2 and HSPF2
SEER2 describes seasonal cooling efficiency. HSPF2 describes seasonal heating efficiency for a heat pump, using the defined Region IV heating season. Both relate delivered heating or cooling to electricity consumed and are expressed in BTU/Wh. Higher values indicate higher efficiency under the applicable test conditions.
The “2” identifies the newer test method. Treat SEER and SEER2, or HSPF and HSPF2, as different reported metrics; this catalog does not convert one into the other. Definitions are published in the ENERGY STAR heat pump criteria.
AFUE
Annual fuel utilization efficiency describes useful heating output relative to fuel input over a heating season, expressed as a percentage. It is the efficiency field used for furnaces and boilers here. The Department of Energy furnace reference explains the metric and separates it from output capacity.
COP, EER and IEER
COP is heating output divided by electrical input in the same units; it has no unit. The operating conditions matter: a COP reported at 5°F (−15°C) describes a different rating point from one at 47°F (8.3°C). Geothermal records retain the reported loop and equipment type beside COP and cooling EER.
EER describes cooling efficiency at specified test conditions in BTU/Wh. IEER is an integrated part-load cooling metric used for commercial equipment. EER, EER2 and IEER remain separately labeled; this reference does not treat them as equivalent. The source datasets for geothermal heat pumps and light commercial HVAC retain each reported metric.
How this catalog displays the numbers
- A heat pump model card shows the lowest and highest values across its published source records, with component coverage labeled separately.
- The best SEER2 and best HSPF2 can come from different rows. Open the model and choose a configuration before comparing.
- Furnace cards display AFUE. A heat pump’s HSPF2 cannot be compared numerically with a furnace’s AFUE percentage.
- Capacity is shown separately in BTU/h or kBTU/h (1 kBTU/h = 1,000 BTU/h); it is not an efficiency rating.
- A missing value stays missing. We do not substitute a manufacturer’s advertised maximum.
What the ratings cannot tell you
This reference does not calculate a home’s energy use, payback, required capacity or operating temperature limit. A seasonal rating alone is not enough to determine any of those. The cold climate label is the designation in the source record, not a building-specific recommendation.