EER (Energy Efficiency Ratio) is cooling BTU divided by watts at a single steady condition — 95°F outdoors. It's the honest worst-case number. SEER averaged efficiency across a simulated season of varying temperatures, flattering modulating equipment. SEER2 keeps the seasonal averaging but raises the test's duct static pressure to better reflect real installations; a unit rated SEER 16 lands near SEER2 15.2.
Since 2023: SEER2 13.4 in northern states and SEER2 14.3 in southern states for split-system central AC (with corresponding EER2 floors in the southwest). High-efficiency tiers run SEER2 17–22+ with variable-speed compressors.
Each SEER2 point is roughly a 5–7% energy saving at typical loads. Going from SEER2 14.3 to 17 on a 3-ton system at $0.17/kWh and 8 h/day saves on the order of $15–20 a month in season — work your own numbers in the bill calculator.
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Not always — the premium for very high SEER2 equipment pays back fastest in long cooling seasons (Sun Belt) and high electricity rates. In short-season northern climates a mid-tier unit often wins on total cost.
Approximately: SEER2 ≈ SEER × 0.95 for typical ducted systems. Compare like for like when reading older spec sheets.
Put the numbers to work: AC tonnage calculator · bill calculator · model number decoder.