SEER2 measures seasonal cooling efficiency, EER2 measures cooling efficiency at a specified test condition, and HSPF2 measures seasonal heating efficiency for heat pumps.
All three use Btu/Wh (British thermal units per watt-hour): how much heating or cooling the equipment delivers for each watt-hour of electricity. Higher is better within the same rating, but you cannot compare 12 EER2 directly with 18 SEER2. A higher rating also does not mean your whole electric bill falls by the same percentage.
SEER2 vs EER2 vs HSPF2 at a Glance
| Rating | What it measures | Rating conditions | Used for | Units |
|---|---|---|---|---|
| SEER2 | Cooling output compared with electricity consumed over a standardized cooling season | A seasonal calculation based on multiple operating conditions | Central AC and air-source heat pumps | Btu/Wh |
| EER2 | Cooling capacity compared with electric power input at a defined test point | Standard full-load rating at 95°F outdoor temperature | Central AC and air-source heat pumps, when reported | Btu/Wh |
| HSPF2 | Heating delivered compared with electricity consumed over a standardized heating season | A seasonal calculation using defined heating-weather assumptions | Air-source heat pumps | Btu/Wh |
These are U.S. residential central-system ratings. Room air conditioners and some commercial equipment use other metrics, including CEER and IEER. EER2 is not always published: DOE makes it optional for models not subject to EER2-based regional standards.
What Is SEER2?
SEER2 stands for Seasonal Energy Efficiency Ratio 2. It compares the amount of heat an air conditioner or heat pump removes from a home over a standardized cooling season with the electricity the system uses during that period.
For example, an 18 SEER2 system has a better seasonal cooling efficiency rating than a 15 SEER2 system when both are evaluated under the same test method. That comparison says nothing by itself about whether either system is correctly sized for your house or installed with adequate airflow.
SEER2 is generally the first efficiency figure to compare when you are evaluating residential cooling equipment. It is a seasonal laboratory-derived rating, not a prediction of how many kilowatt-hours your particular home will use next summer.
What Is EER2?
EER2 stands for Energy Efficiency Ratio 2. Unlike SEER2, it describes cooling performance at a specified operating condition rather than combining results across a simulated cooling season.
For residential central systems under the DOE Appendix M1 method, the standard full-load EER2 rating uses an outdoor temperature of 95°F and indoor air at 80°F dry-bulb and 67°F wet-bulb. The two indoor measurements set standardized temperature and moisture conditions for the test. EER2 therefore helps compare cooling performance at one common hot-weather test point.
That does not make EER2 an exact forecast for a 105°F afternoon in inland Orange County. Actual efficiency changes with outdoor temperature, indoor conditions, airflow and the way the system operates. For performance at more extreme temperatures, check the manufacturer's expanded performance data.
Can the two ratings favor different systems? Yes. One system may score higher for seasonal cooling (SEER2) but lower at the full-load EER2 test point. To compare two models fairly, check each rating against the same rating on the other model.
What Is HSPF2?
HSPF2 stands for Heating Seasonal Performance Factor 2. It measures how much heating an air-source heat pump provides over a standardized heating season relative to the electrical energy consumed. The standard U.S. HSPF2 rating uses Region IV, a defined set of heating-season outdoor temperatures and their frequency. It is not based on the actual winter weather at your home.
HSPF2 is relevant only when the equipment operates as a heat pump in heating mode. A conventional cooling-only central AC does not have an HSPF2 rating. A gas furnace uses a different efficiency measure—Annual Fuel Utilization Efficiency (AFUE), reported as a percentage.
There is also an important limit: HSPF2 does not tell you how much heat a unit can deliver at a specific low outdoor temperature. If winter heating performance is important, review the rated heating capacity and coefficient of performance (COP) at the temperatures that matter for the installation, along with any auxiliary-heat requirements.
Why Do These Ratings End in “2”?
The U.S. Department of Energy moved residential central air conditioners and heat pumps to an updated testing procedure, known as Appendix M1, beginning in 2023. The newer ratings—SEER2, EER2 and HSPF2—reflect revised test conditions, including changes to how ducted-system external static pressure is represented.
Old SEER and new SEER2 numbers are not interchangeable. A system labeled 16 SEER under the older procedure is not necessarily equivalent to a system labeled 16 SEER2. The same caution applies to EER versus EER2 and HSPF versus HSPF2. When comparing an older unit with a new quote, identify which test method produced each number before making a numerical comparison.
Which Ratings Apply to AC, Heat Pumps and Other Equipment?
Cooling-only central AC
Look for SEER2 and, where published, EER2. HSPF2 does not apply because the equipment does not provide heat-pump heating.
Central air-source heat pump
Check SEER2 for cooling and HSPF2 for heating. Compare EER2 when reported for hot-weather cooling. A high cooling rating does not automatically mean a high heating rating.
Ductless mini-split heat pump
Compare SEER2 and HSPF2, plus EER2 if reported. Check the certified indoor/outdoor combination, especially for multi-zone systems.
Gas furnace or other equipment
Gas furnaces use AFUE. Room air conditioners and many commercial HVAC products use other rating systems; do not compare their numbers directly with SEER2.
A packaged air conditioner or heat pump may also be rated with these metrics, depending on its regulated equipment class. Always compare products within the appropriate category.
Why a Higher Rating Does Not Guarantee the Same Percentage in Bill Savings
Efficiency ratings express energy use relative to heating or cooling delivered under standardized conditions. Your electric bill covers much more than that equipment's rated cooling or heating operation.
An illustrative SEER2 comparison
Assume two systems each deliver 24 million Btu of cooling under the same simplified seasonal-rating assumptions:
15 SEER2 → 1,600 kWh of cooling electricity
20 SEER2 → 1,200 kWh of cooling electricity
The second system uses 25% less cooling electricity in this example—not 25% less electricity for the entire home. The calculation illustrates the rating relationship; it is not a site-specific savings forecast.
In a real home, several factors can change the result:
Building and weather
Insulation, solar gain, thermostat settings, outdoor temperatures and how often the system runs determine the load it must serve.
Installed performance
Duct leakage, restrictive airflow, incorrect refrigerant charge, equipment mismatch and control settings can keep the system from performing as rated.
Utility costs
Electricity rate schedules, fixed charges and other household loads affect the total bill. Heat-pump heating costs also depend on how much backup heat is used.
To estimate dollar savings, look at the home's cooling load, current energy use, proposed system and electric rates. The SEER2 number alone cannot predict a household's annual savings.
How to Compare HVAC Efficiency Ratings Before You Buy
When reviewing two installation quotes, compare the ratings for the exact equipment combinations being offered, not the best number in a product-family advertisement.
Which rating should you look at?
- Central AC: Compare SEER2, then EER2 if available—especially where summer afternoons are hot.
- Heat pump: Compare SEER2 for cooling and HSPF2 for heating; check EER2 where reported.
- Two installation quotes: Request the AHRI-certified values for each proposed indoor/outdoor combination.
- Identify the system type. For cooling-only AC, compare cooling ratings. For a heat pump, review cooling and heating ratings separately.
- Compare the same metric. Check SEER2 against SEER2, EER2 against EER2, and HSPF2 against HSPF2—not one rating against another.
- Request the exact matched-system rating. Ask for the AHRI Certified Reference Number or Certificate of Product Ratings showing the proposed outdoor and indoor equipment.
- Check capacity as well as efficiency. Confirm that the proposed equipment is sized for the home's heating and cooling loads. A high efficiency rating cannot correct an inappropriate capacity.
- Consider local weather and operating costs. In Orange County, EER2 can add context for hot-afternoon cooling. For a heat pump, HSPF2 also matters when comparing winter electricity use.
- Ask what the installation includes. Duct repairs, airflow adjustments, controls, and startup verification can matter more than a small difference between advertised ratings.
Why the AHRI number matters: For a split system, the certified efficiency applies to a particular tested or certified combination of components. An outdoor unit advertised as “up to 20 SEER2” does not guarantee 20 SEER2 when paired with a different indoor coil or air handler. You can verify an AHRI reference through the AHRI Directory.
Efficiency ratings measure standardized energy performance. Single-stage, two-stage and variable-speed AC describes how equipment adjusts output—a separate question from its efficiency rating.
Whichever rating you choose, an AC replacement or heat pump installation estimate should explain the proposed sizing and airflow checks.
Frequently Asked Questions
Is SEER2 or EER2 more important?
SEER2 is better suited to comparing standardized seasonal cooling efficiency. EER2 adds a comparison at a specific hot-weather rating condition. For homes with substantial hot-afternoon cooling demand, it is useful to look at both.
Is a higher SEER2 rating always better?
A higher SEER2 means higher rated seasonal cooling efficiency under the same test procedure. It does not automatically make that system the better purchase once equipment price, sizing, installation quality and expected usage are considered.
Does a heat pump have SEER2 and HSPF2?
Yes. Residential air-source heat pumps are rated for seasonal cooling with SEER2 and seasonal heating with HSPF2. EER2 may also be reported to show cooling efficiency at a defined hot-weather test point, but it is not mandatory for every model.
Can I compare SEER with SEER2?
Not as equal numbers. The test procedure changed. Compare products rated under the same procedure or use manufacturer or AHRI documentation that identifies the rating basis.
Does HSPF2 show how well a heat pump heats on a freezing day?
No. HSPF2 is a seasonal efficiency measure. To evaluate cold-weather operation, ask for heating capacity and efficiency at specified outdoor temperatures, including whether auxiliary heat is expected.
Do gas furnaces have HSPF2 ratings?
No. Gas furnaces are typically described by AFUE, a percentage-based fuel-efficiency rating. HSPF2 applies to electric heat-pump heating and should not be compared numerically with AFUE.
Technical References
- DOE — 10 CFR Appendix M1 (residential AC and heat-pump test method): standard rating conditions and when EER2 reporting is optional.
- AHRI — 2023 Energy Efficiency Standards: why the updated residential ratings were introduced.
- ENERGY STAR — Heat Pump Equipment Key Product Criteria: definitions and rating applications.
- AHRI — How and Why Equipment Is Certified: matched-system ratings and certification numbers.
Bottom line: Use SEER2 to compare seasonal cooling efficiency, EER2 to compare cooling efficiency at a common test point, and HSPF2 to compare heat-pump heating efficiency. Choose from the ratings certified for the exact proposed equipment, then evaluate sizing, installation and likely operating conditions before assuming one quote will cost less to run.