SEER (Seasonal Energy Efficiency Ratio) measures how many BTUs of cooling an air conditioner or heat pump produces per watt-hour of electricity consumed, averaged over an entire cooling season. A higher SEER number means the unit uses less electricity to deliver the same amount of cooling. A 16 SEER air conditioner uses about 25% less electricity than a 12 SEER unit for identical cooling output.
Think of SEER like miles per gallon for your car — it tells you how far your energy dollar goes. Just as a 30 MPG car costs less to drive than a 20 MPG car, a 20 SEER AC costs less to operate than a 14 SEER AC.
The SEER Formula
SEER is calculated as:
SEER = Total Cooling Output (BTU) / Total Electrical Input (Wh)
The "seasonal" part is critical. SEER isn't measured at one temperature. It's calculated across a range of outdoor temperatures from 65 degrees F to 104 degrees F, weighted by the typical number of hours a region experiences each temperature during a cooling season. This makes SEER a composite number that reflects real-world seasonal performance, not just peak-day efficiency.
The test assumes a constant indoor temperature of 80 degrees F with 50% relative humidity. The system cycles on and off naturally as the cooling load changes with outdoor temperature.
Important: SEER was replaced by SEER2 on January 1, 2023. New equipment manufactured after that date uses SEER2 ratings, which are about 4.7% lower due to a tougher testing procedure. If you're shopping for a new AC in 2026, you'll see SEER2 on the label. This article covers the original SEER for reference, since millions of existing systems still carry SEER ratings.
What SEER Numbers Mean in Practice
*Based on a 3-ton system, 1,500 cooling hours, $0.16/kWh.
How SEER Translates to Electricity Use
For a specific calculation, use this formula:
Annual Cooling kWh = (BTU Capacity x Annual Cooling Hours) / (SEER x 1,000)
For a 3-ton (36,000 BTU/h) AC running 1,500 hours per year at 16 SEER:
36,000 x 1,500 / (16 x 1,000) = 3,375 kWh per year
At $0.16/kWh, that's $540 per year in cooling costs. The same system at 12 SEER would use 4,500 kWh and cost $720 — a difference of $180 per year.
How SEER Is Tested
The SEER test procedure (before the 2023 SEER2 change) worked as follows:
The system is set up in a controlled laboratory with two sealed chambers — one representing "indoor" and one representing "outdoor." Temperatures are varied across eight operating conditions (called temperature bins) ranging from 65 to 104 degrees F. The system runs at each condition long enough to reach steady-state performance. Total cooling output (BTU) and total electrical input (watt-hours) are measured at each bin. The results are weighted by the typical hours at each temperature for a representative U.S. cooling season. Single-stage units cycle on and off; two-stage and variable-speed units operate at their various capacity levels.
The test uses external static pressure of approximately 0.1 inches of water column (in. w.c.), which represents very low duct resistance. This is one of the key criticisms that led to the SEER2 update, which uses 0.5 in. w.c.
SEER History and Federal Minimums
If your home has an AC installed before 2006, it likely runs at 10-12 SEER. Systems from 2006-2014 are at least 13 SEER. Modern units range from 14 to 26+ SEER (or their SEER2 equivalents).
SEER vs SEER2: The Transition
Since January 2023, SEER has been officially replaced by SEER2 for all newly manufactured equipment. The key difference is the testing procedure:
SEER used approximately 0.1 in. w.c. external static pressure, essentially assuming perfect ductwork. SEER2 uses 0.5 in. w.c. from the M1 test procedure, simulating typical residential duct conditions.
Because the SEER2 test makes the system work harder, SEER2 numbers are roughly 4.7% lower than SEER for the same equipment. A unit that rated 16 SEER now rates about 15.3 SEER2. The equipment itself didn't change, only the yardstick.
When comparing ACs, make sure you're comparing the same rating type. A 15 SEER2 unit is actually more efficient than a 15 SEER unit, even though the numbers are the same. Always check which standard the rating uses before making purchasing decisions.
What Affects Your Actual SEER Performance
Your real-world efficiency will differ from the laboratory SEER rating. Several factors can push your actual efficiency above or below the rated SEER:
Ductwork condition is the biggest variable. The DOE estimates that 20-30% of conditioned air is lost through leaky ducts in typical homes. A 16 SEER system with 25% duct losses effectively performs like a 12 SEER system.
Proper sizing matters more than most people realize. An oversized AC short-cycles, running in brief bursts that waste energy on startup and reduce dehumidification. A unit sized correctly via Manual J load calculation runs longer, steadier cycles at better efficiency.
Installation quality accounts for up to 30% of a system's real-world performance, according to ACCA. Refrigerant charge, airflow rates, electrical connections, and duct sealing all affect efficiency.
Maintenance habits like changing filters, cleaning coils, and keeping the outdoor unit clear maintain the system near its rated SEER. Neglect can reduce efficiency by 5-15% over several years.
Thermostat settings and usage patterns also matter. A smart thermostat that raises the setpoint when you're away can save 10-15% on cooling costs, effectively making a 14 SEER system perform like a 16 SEER system in terms of total energy use.
SEER and Different Compressor Types
The compressor type is the primary determinant of a system's SEER rating:
Variable-speed systems achieve high SEER ratings because they spend most of their operating time at low-speed, part-load conditions where they're most efficient. The SEER test captures this advantage because it includes many hours at lower outdoor temperatures where variable-speed units cruise at minimal capacity.
Finding Your Current System's SEER Rating
If you want to know your existing AC's SEER rating, here are your options:
Check the yellow EnergyGuide label on the outdoor unit or in the installation paperwork. This prominently displays the SEER rating.
Look up the model number at the AHRI certification directory (ahridirectory.org). The model number is on the data plate of the outdoor unit. Enter it to find the certified SEER, EER, and other ratings for that specific indoor/outdoor combination.
Estimate by age. Pre-1992: likely 6-10 SEER. 1992-2005: 10-12 SEER. 2006-2014: 13-14 SEER. 2015-2022: 14-16 SEER (varies by region). Post-2022: check SEER2 rating instead.
Check the refrigerant type. Systems using R-22 (Freon) are at least 10 years old (it was phased out of new equipment in 2010) and typically 10-14 SEER. Systems using R-410A are newer and more likely to be 13+ SEER.
Key Takeaways
- SEER = Total Cooling BTU / Total Watt-Hours over a full cooling season. Higher SEER means lower electricity costs.
- SEER was replaced by SEER2 in January 2023. SEER2 numbers are about 4.7% lower due to more realistic testing.
- Each SEER point upgrade saves roughly $20-$40/year for a typical 3-ton system at $0.16/kWh.
- Variable-speed compressors achieve the highest SEER ratings (18-26+) due to efficient part-load operation.
- Real-world efficiency depends on ductwork, sizing, installation, and maintenance as much as the SEER rating itself.
- If your system is from before 2006, it's likely 10-12 SEER. Upgrading to a modern 16 SEER2 system could cut cooling costs by 30-40%.
- SEER is a seasonal average, not peak-day performance. For hot-day efficiency, look at EER or EER2.
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