AC Efficiency Ratings Explained: SEER, SEER2, and EER

What SEER and SEER2 Mean

SEER stands for Seasonal Energy Efficiency Ratio. It measures the total cooling output of an air conditioner over an entire cooling season divided by the total electrical energy consumed during that period. The result is expressed in BTU per watt-hour. A system rated at SEER 16 produces 16 BTU of cooling for every watt-hour of electricity consumed, averaged over a full season of varying temperatures and conditions.

SEER2 uses the same fundamental calculation but measures performance under the updated M1 testing procedure established by the Department of Energy in 2023. The M1 procedure adds external static pressure to the indoor unit during testing, simulating the real-world resistance of ductwork that the original SEER test did not account for. Because the system has to push air against this added resistance, SEER2 numbers come out roughly 4.7 percent lower than the equivalent SEER number. A system that tested at SEER 16 under the old procedure would test at approximately SEER2 15.2 under the new procedure, even though its actual performance has not changed.

This distinction matters when you are comparing an older system's SEER rating to a new system's SEER2 rating. To convert SEER to SEER2, multiply the SEER number by 0.953. To convert SEER2 to SEER, divide by 0.953 (or multiply by 1.049). For example, a SEER2 15.2 system is equivalent to approximately SEER 16.0. When a contractor quotes a SEER2 15 system, they are offering efficiency equivalent to the old SEER 15.7.

What EER and EER2 Mean

EER (Energy Efficiency Ratio) measures cooling efficiency at a single test condition: 95 degrees Fahrenheit outdoor temperature, 80 degrees indoor temperature, and 50 percent indoor humidity. Unlike SEER, which averages performance across a range of temperatures throughout a season, EER captures peak-condition performance. EER2 applies the same M1 testing procedure update that SEER2 uses, resulting in slightly lower numbers than the original EER.

EER matters most in hot climates where the air conditioner operates at or near full capacity for extended periods. In Phoenix, Las Vegas, Houston, and similar markets where summer temperatures routinely exceed 95 degrees for months, a high EER rating translates directly to lower electricity bills during the hottest parts of the season. In cooler climates like the Pacific Northwest or the northern Midwest, SEER2 is the more relevant rating because the system spends most of its operating time at partial load conditions that SEER2 captures better.

Most residential AC systems have an EER2 rating of 10 to 13. High-efficiency models reach EER2 13 to 15. When comparing systems for a hot climate installation, pay attention to EER2 rather than focusing solely on SEER2, because two systems with identical SEER2 ratings can have meaningfully different EER2 ratings that affect your peak-season electricity consumption.

Current Federal Minimum Standards

The Department of Energy sets minimum efficiency standards for residential air conditioning equipment sold in the United States. As of 2023, the minimums are split by region to account for the different cooling demands of northern and southern climates.

Northern region (states above the Sun Belt line): SEER2 14.3, EER2 not specified for split systems. This region includes states where cooling is a seasonal need rather than a year-round requirement, so a lower minimum reflects the reduced total energy impact of less efficient cooling equipment.

Southern region (Sun Belt states including the Southeast, Southwest, and Gulf Coast): SEER2 15.2, EER2 11.7 for split systems. The higher minimums in this region reflect the greater cooling hours and energy consumption that make equipment efficiency a larger factor in total household energy costs.

These are floor values, meaning all new equipment must meet or exceed them. The actual range of available equipment spans from SEER2 14.3 to SEER2 26+ for residential split systems. Higher efficiency levels correspond to higher equipment costs, creating a decision point between upfront investment and long-term energy savings.

Efficiency Tiers and What They Cost

Residential AC systems fall into three general efficiency tiers, each with a different price point and target buyer.

Base tier (SEER2 14.3 to 15.2): These are the minimum-efficiency systems that meet but do not exceed federal standards. They use single-stage compressors that run at full capacity whenever they are on, which means they cycle on and off throughout the day. Equipment cost for the outdoor unit runs $1,200 to $2,000, with total installed system cost of $4,500 to $7,000 depending on size and installation complexity. Base tier systems are the most affordable upfront but have the highest operating costs.

Mid tier (SEER2 16 to 18): These systems use either two-stage compressors (which run at a lower speed most of the time and shift to high speed only on the hottest days) or improved single-stage designs with better components. Two-stage operation delivers more consistent temperatures, lower noise, and better humidity control compared to single-stage systems. Equipment cost is $1,800 to $3,000, with installed system cost of $5,500 to $9,000. The energy savings over base tier typically cover the price difference within 5 to 8 years in moderate to hot climates.

High tier (SEER2 19 to 26+): These systems use variable-speed (also called inverter-driven) compressors that continuously adjust their output to match the current cooling demand. Instead of cycling on and off, the compressor runs at low speed when the load is light and ramps up gradually as demand increases. The result is exceptionally consistent temperatures (within 0.5 degrees of the setpoint), very quiet operation (as low as 55 decibels outdoors), superior humidity control, and the lowest operating costs. Equipment cost is $2,500 to $5,000+, with installed system cost of $7,000 to $12,000+. These systems deliver the best long-term value in hot climates where the AC runs many hours per year but carry the highest upfront cost. See our replacement cost guide for detailed pricing by size and tier.

Calculating Your Energy Savings

You can estimate the annual cooling cost for any efficiency rating using this formula: divide 12,000 by the SEER2 rating to get watts per ton-hour, multiply by your system tonnage, multiply by the number of cooling hours per year, then multiply by your electricity rate per kilowatt-hour.

For a practical example, consider a 3-ton system in a climate with 1,200 cooling hours per year and an electricity rate of $0.14 per kilowatt-hour. At SEER2 15: (12,000 / 15) x 3 x 1,200 x 0.00014 = $403 per year. At SEER2 20: (12,000 / 20) x 3 x 1,200 x 0.00014 = $302 per year. The SEER2 20 system saves $101 per year, or $1,515 over a 15-year equipment life. The savings increase in hotter climates with more cooling hours and in areas with higher electricity rates.

Your actual cooling hours depend on your climate zone. Southern Florida, the Gulf Coast, and the desert Southwest see 2,000 to 3,000 cooling hours per year. The mid-South and Mid-Atlantic states see 1,000 to 1,800 hours. The northern states see 400 to 1,000 hours. You can estimate your cooling hours by dividing your summer electricity usage (above your non-cooling baseline) by your system's approximate power draw, or by checking your utility's climate zone data.

What About Heat Pump Efficiency

Heat pumps use the same SEER2 rating for cooling efficiency, plus an HSPF2 (Heating Seasonal Performance Factor 2) rating for heating efficiency. When evaluating a heat pump, both ratings matter because the system serves dual duty. A heat pump with SEER2 16 and HSPF2 8.5 provides good cooling efficiency and adequate heating efficiency. A high-end unit might achieve SEER2 22 and HSPF2 10, delivering excellent performance in both modes.

For homeowners considering a heat pump to replace both their air conditioner and furnace, the combined energy savings from efficient cooling and efficient heating often produce a stronger financial case for high-efficiency equipment than cooling alone. Federal tax credits under the Inflation Reduction Act provide up to $2,000 for qualifying heat pumps meeting the highest efficiency tier (currently CEE Tier 1 or higher), which further improves the return on investment for high-efficiency heat pump systems.

Comparing Your Old System to New Options

To understand the potential savings from upgrading, you need to know your current system's efficiency. If your system was manufactured before 2006, it likely has a SEER rating of 10 to 12 (the minimum was SEER 10 until 2006). Systems from 2006 to 2015 have minimum SEER 13. Systems from 2015 to 2022 have minimum SEER 14. Systems from 2023 onward have SEER2 14.3 to 15.2 minimums.

The efficiency gap between a 15-year-old system and a modern high-efficiency system is substantial. A SEER 10 system from 2009 uses roughly 50 percent more electricity than a SEER2 15 system and 100 percent more electricity than a SEER2 20 system for the same cooling output. Even accounting for the fact that your old system may have lost additional efficiency due to age-related wear, the upgrade from a 15-year-old SEER 10 system to a modern SEER2 16 system typically saves $300 to $500 per year in a warm climate.

Our system age guide helps you evaluate whether your current system's age and efficiency level justify replacement, and our repair or replace guide provides the decision framework for choosing between keeping your current equipment and upgrading.