SEER vs SEER2 Explained: Understanding the 2023 AC Efficiency Changes

What Is SEER2?

SEER2 (Seasonal Energy Efficiency Ratio 2) is an updated testing standard for measuring air conditioner and heat pump efficiency. Introduced by the Department of Energy in January 2023, SEER2 uses testing procedures that more accurately reflect real-world installation conditions.

The key difference is that SEER2 tests equipment with higher static pressure in the ductwork, simulating the increased airflow resistance found in typical residential installations. This means SEER2 ratings are generally lower than SEER ratings for the same equipment because the testing conditions are more demanding.

Think of it this way: the original SEER test was like testing a car's fuel economy on a perfectly smooth track with ideal conditions. SEER2 is more like testing on actual roads with traffic, stop signs, and hills. The car is the same, but the more realistic test shows somewhat lower numbers.

Why Did the Standards Change?

The Department of Energy updated testing standards for several important reasons:

More Realistic Testing Conditions

The original SEER testing used 0.1 inches of water column (in. w.c.) of external static pressure to simulate ductwork resistance. However, studies showed that most residential duct systems have significantly higher static pressure, often 0.5 in. w.c. or more. SEER2 testing uses 0.5 in. w.c. for ducted systems, providing results more representative of actual installed performance.

Better Consumer Information

When equipment performs differently in the lab than in homes, consumers can't accurately predict their energy costs. SEER2 ratings should better match real-world energy consumption, helping homeowners make more informed purchasing decisions.

Encouraging Better Installations

The new standards also incentivize HVAC contractors to install properly designed duct systems. When efficiency ratings assume realistic ductwork resistance, there's more attention paid to duct design and installation quality.

Alignment with Industry Reality

The HVAC industry has evolved significantly since the original SEER testing protocols were established. Modern equipment, with variable-speed blowers and ECM motors, performs differently at various static pressures. The updated testing better captures this performance variation. For more on evolving HVAC standards, see ASHRAE.

SEER vs SEER2: Key Differences

Understanding the technical differences between SEER and SEER2 testing helps interpret ratings correctly:

The most important thing to understand is that SEER2 ratings are lower than SEER ratings for equivalent efficiency. A unit rated 15 SEER2 is comparable to one rated about 15.7 SEER under the old system. The equipment didn't get less efficient; the test simply became more stringent.

SEER to SEER2 Conversion

To compare equipment rated under different standards, you need to convert between SEER and SEER2. The approximate conversion factor is:

This means SEER2 ratings are approximately 4.5% lower than equivalent SEER ratings. Conversely:

SEER to SEER2 Conversion Chart

New Minimum Efficiency Requirements

Along with the change to SEER2 testing, the Department of Energy implemented new minimum efficiency standards effective January 1, 2023. These standards vary by region and equipment type:

Central Air Conditioners

Heat Pumps

Regional Definitions

The Department of Energy divides the country into regions based on typical cooling needs:

• North: All states not listed below
• Southeast: Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia
• Southwest: Arizona, California, Nevada, New Mexico

The Southeast and Southwest regions have higher minimum requirements because air conditioning is used more extensively in these areas, making efficiency more impactful on total energy consumption.

HSPF2 and EER2

The transition to more realistic testing standards also affected other efficiency metrics:

HSPF2 (Heating Seasonal Performance Factor 2)

For heat pumps, heating efficiency is now measured by HSPF2 instead of HSPF. Like SEER2, HSPF2 uses higher static pressure in testing, resulting in ratings approximately 4-5% lower than equivalent HSPF values.

Minimum HSPF2 requirements are 7.5 for all regions, equivalent to approximately 7.8 HSPF under the old testing method.

EER2 (Energy Efficiency Ratio 2)

The peak efficiency metric EER has also been updated to EER2 with similar testing changes. EER2 ratings are approximately 4-5% lower than equivalent EER ratings.

Non-Ducted Equipment

For ductless mini-split systems, the testing conditions are different since they don't connect to ductwork. These systems are tested at 0.0 in. w.c. external static pressure, so the difference between SEER and SEER2 is smaller for ductless equipment.

What This Means for Consumers

The transition to SEER2 has several practical implications for homeowners shopping for new HVAC equipment:

Don't Be Alarmed by Lower Numbers

If a new air conditioner is rated 15.3 SEER2, it's not less efficient than a unit rated 16 SEER under the old system. They're approximately equivalent. The new numbers are lower because the test is more demanding, not because equipment got less efficient.

Compare Apples to Apples

When comparing equipment, make sure you're comparing SEER to SEER or SEER2 to SEER2. Mixing the metrics leads to incorrect conclusions. If you need to compare across standards, use the conversion factors provided above.

More Accurate Energy Estimates

SEER2 ratings should provide better predictions of actual energy consumption and costs. When you calculate savings using SEER2 ratings, the results should more closely match your real utility bills.

Installation Quality Matters Even More

Since SEER2 testing assumes typical (not ideal) duct conditions, the rated efficiency assumes adequate ductwork. If your ducts are undersized, leaky, or poorly designed, actual performance may still fall short of ratings. Quality installation remains crucial.

Older Units Still Use SEER

Equipment manufactured before 2023 was rated using the original SEER standard. When comparing your existing unit to new options, you may need to convert between standards for accurate comparison.

Transitional Issues and Inventory

The 2023 transition created some complexity regarding equipment manufactured before and after the change:

Pre-2023 Inventory

Equipment manufactured before January 1, 2023, can still be sold and installed with its original SEER rating. Some distributors had inventory of "old standard" equipment that remained legal to sell even after the transition. This inventory has largely been depleted by now.

Matched Systems

Split systems require matched indoor and outdoor components. If you're replacing only one component, ensuring compatibility with existing equipment (potentially rated under the old standard) may require working with a knowledgeable contractor.

Documentation

New equipment documentation should clearly indicate SEER2 ratings. If you see SEER ratings on new equipment without the "2" designation, it may be pre-transition stock or the rating may need verification.

Rebates and Tax Credits

Federal tax credits and utility rebates have been updated to reference SEER2 thresholds where applicable. Make sure you're checking current program requirements, as older documentation may still reference SEER. For example, federal tax credits may require 16 SEER2 (equivalent to about 16.8 SEER) rather than the old 16 SEER threshold.

Impact on Energy Calculations

If you're using our SEER Calculator or similar tools, the fundamental calculations remain the same. The efficiency formula is unchanged; only the rating numbers are different.

Using SEER2 in Calculations

The annual energy calculation works identically with SEER2:

Simply use the SEER2 value where you previously used SEER. The results should be slightly more conservative (predicting slightly higher energy use) because SEER2 ratings are lower.

Comparing Old and New Equipment

To compare an existing unit rated in SEER to a new unit rated in SEER2:

1. Convert the old SEER to SEER2: multiply by 0.955
2. Compare both values in SEER2 terms
3. Calculate savings using consistent units

Example: Your current 10 SEER unit (≈ 9.55 SEER2) compared to a new 15.3 SEER2 unit shows a 60% efficiency improvement (9.55 to 15.3), not the 53% improvement you'd get comparing 10 SEER to 16 SEER incorrectly.

Frequently Asked Questions

Is equipment with a SEER2 rating less efficient than SEER?

No. The same physical equipment simply has a lower number under SEER2 because the test is more demanding. A unit rated 15.3 SEER2 is essentially equivalent to one rated 16 SEER. The equipment didn't change; the testing did.

Can I still buy equipment rated with the old SEER?

Potentially, if a contractor has remaining inventory manufactured before 2023. However, this inventory has largely been sold. All new equipment manufactured since January 2023 must be rated using SEER2.

Do I need to use a different formula to calculate energy costs with SEER2?

No. The formula is identical. Just use the SEER2 rating where you previously used SEER. The results will be slightly more conservative, which better matches real-world performance.

How do I compare my old AC to new SEER2 equipment?

Convert your old SEER rating to SEER2 by multiplying by 0.955, then compare. For example, if your old unit is 10 SEER, that's approximately 9.55 SEER2. A new 15 SEER2 unit would be about 57% more efficient.

Do minimum efficiency requirements change by region?

Yes. The South (Southeast and Southwest regions) requires 14.3 SEER2 minimum, while the North requires 13.4 SEER2 minimum. This reflects higher cooling needs in southern climates.

What about ductless mini-splits?

Ductless systems are tested without external static pressure since they don't use ducts. The SEER to SEER2 difference is smaller for these systems, typically less than 1-2%.

Have federal tax credits changed with SEER2?

Yes, program requirements have been updated to SEER2 thresholds. Check current requirements before purchasing, as threshold values differ from the old SEER-based requirements.

Practical Tips for Equipment Shopping

Keep these guidelines in mind when shopping for new AC equipment:

Ask for SEER2 Ratings

Ensure contractors quote SEER2 ratings for new equipment. If they mention SEER without the "2," ask for clarification about whether the equipment is new or pre-transition stock.

Verify Ratings

Check the AHRI Directory to verify equipment ratings. The database now shows SEER2 ratings for new certified products.

Request Proper Documentation

Your installation documentation should include the SEER2 rating, which you'll need for rebate applications and future reference.

Focus on Comparison Shopping

When comparing quotes, ensure all are quoting in the same efficiency metric. Don't assume a "16 SEER" quote and a "15.3 SEER2" quote represent different efficiency levels - they may be essentially equivalent.

Consider the Complete System

SEER2 testing assumes typical duct resistance. If your ductwork is particularly restrictive or in poor condition, even a high-SEER2 system may not perform optimally. Ask about duct evaluation as part of any replacement project.

The Bigger Picture

The transition to SEER2 is part of broader efforts to ensure efficiency ratings reflect real-world performance. While the change may cause temporary confusion as the market adjusts, it ultimately benefits consumers by providing more accurate information.

Future Efficiency Improvements

Equipment manufacturers continue to improve efficiency. Variable-speed and inverter-driven systems now achieve SEER2 ratings above 20, providing exceptional efficiency even under the more demanding test conditions.

Better Installation Practices

The new standards also highlight the importance of quality ductwork. As ratings assume typical duct resistance, there's increased awareness that poorly designed or installed ducts limit system performance regardless of equipment efficiency.

Energy Code Evolution

Building codes and energy standards are aligning with SEER2 requirements. New construction will reference SEER2 minimums, and some local codes may require efficiency above federal minimums.

Conclusion

The transition from SEER to SEER2 represents a positive change for consumers, providing more realistic efficiency ratings that better predict actual energy costs. Key points to remember:

• SEER2 uses more demanding testing conditions with higher static pressure
• SEER2 ratings are approximately 4.5% lower than equivalent SEER ratings
• The equipment didn't get less efficient; the test became more realistic
• New minimum requirements are 13.4 SEER2 (North) and 14.3 SEER2 (South)
• Compare ratings using the same standard (SEER to SEER or SEER2 to SEER2)
• Calculation formulas work identically with either rating
• Check current rebate and tax credit requirements for updated SEER2 thresholds

Use our SEER Calculator to compare efficiency levels and estimate your potential savings, whether using SEER or SEER2 ratings. The underlying math works the same way with either standard.

Related Guides

• SEER Rating Savings Chart — See exactly how much you save at each efficiency level.
• HVAC Efficiency Calculator Guide — Learn the formulas behind SEER, EER, HSPF, and AFUE.
• What SEER Rating Do I Need? — Find the right efficiency level for your climate and budget.
• EER to SEER Conversion — Convert between EER and SEER ratings.

Sources & References

• U.S. Department of Energy — Central Air Conditioning — Federal efficiency standards and consumer guidance.
• AHRI Directory — Certified equipment ratings database for verifying SEER2 ratings.
• ASHRAE — Standards body for HVAC testing procedures and building performance.
• ENERGY STAR — Heating & Cooling — Efficiency certification thresholds and product finder.
• DOE Building Energy Codes Program — Regional efficiency requirements and building code updates.