What Is SEER Rating?
When you shop for an air conditioner or heat pump in the US, you'll see SEER on the label—and often SEER2 as well. SEER tells you how efficiently the system turns electricity into cooling over a full season, which directly affects your energy bills. This guide explains what SEER means, how it's calculated, why it matters, how US minimums vary by region, and how SEER2 fits in—so you can compare units and make a smarter choice for your home.
What SEER Means and How It's Calculated
SEER stands for Seasonal Energy Efficiency Ratio. It measures how much cooling (in BTU) a central air conditioner or air-source heat pump delivers over a typical cooling season, divided by how much electrical energy (in watt-hours) it uses in that same period. The formula is: total cooling output (BTU) ÷ total electrical input (watt-hours). So a unit that delivers 36,000 BTU of cooling while using 3,000 watt-hours of electricity has a SEER of 12. The higher the SEER, the more cooling you get per unit of electricity—so a SEER 18 system is more efficient than a SEER 14 system.
SEER is a "seasonal" average because it assumes a range of outdoor temperatures and part-load operation over a representative season, not just one test condition. That makes it a more realistic efficiency number for comparing systems. In the US, SEER is determined under federal test procedures so that different brands and models can be compared fairly. Ductless mini-splits and central systems both carry SEER ratings when they fall under the same regulations.
Why SEER Matters for Running Costs
A higher SEER rating means the system uses less electricity to produce the same amount of cooling. For a given cooling load and number of run hours, a SEER 18 unit will use roughly 20% less electricity than a SEER 15 unit, and about 33% less than a SEER 12. Over the life of the system, that difference can add up to hundreds or thousands of dollars in savings, depending on your climate, electricity rate, and usage.
SEER doesn't tell you the right size (BTU) for your home—you still need to match capacity to your cooling load. But once you know the size you need, choosing a higher SEER within your budget will reduce your annual cooling cost. In hot climates where the AC runs for many hours, investing in a higher SEER often pays back quickly; in milder regions the payback may be longer but efficiency still lowers bills and carbon impact.
Minimum SEER Requirements by US Region
US federal standards set minimum SEER levels for central air conditioners and air-source heat pumps. As of January 2023, the nationwide minimum for new split-system central AC and heat pumps is 14 SEER in the North and 15 SEER in the South and Southwest (the "South" region includes states where cooling load is high). So you cannot legally install a new central system below those levels—older units with lower SEER can remain in use until they are replaced.
Many states adopt the federal minimums; some have no additional requirements. A few states or localities set stricter efficiency or environmental rules. When in doubt, check with your contractor or state energy office. For ductless mini-splits, minimum SEER levels also apply and align with the same regional split. Choosing a system at or above the minimum is the baseline; going higher (e.g. SEER 16–20+) further cuts running costs if it fits your budget.
SEER Rating Comparison and Annual Savings
The table below gives a rough idea of how different SEER ratings compare in efficiency and relative annual electricity use. "Estimated annual savings" is versus a baseline SEER 14 system (same cooling load and run hours). Actual savings depend on your climate, thermostat settings, and electricity rate.
| SEER Rating | Relative Efficiency | Est. Annual Savings vs SEER 14 |
|---|---|---|
| SEER 14 | Baseline | — |
| SEER 16 | ~13% less energy | ~$80–$150 |
| SEER 18 | ~22% less energy | ~$140–$260 |
| SEER 20 | ~30% less energy | ~$190–$360 |
Savings ranges assume a typical 3–4 ton central AC in a moderate-to-hot climate; adjust for your system size and local electricity rates.
SEER2 Explained
SEER2 is an updated US federal test procedure that took effect for most new central AC and heat pump systems in 2023. The test uses slightly different conditions (including higher external static pressure to reflect real ductwork) so that the reported efficiency is closer to what you get in a real installation. As a result, SEER2 numbers are typically a bit lower than the old SEER numbers for the same unit—often around 5–8% lower. So a system that was rated 16 SEER might be around 14.5–15 SEER2.
Federal minimums are now expressed in SEER2: the North minimum is 13.4 SEER2 and the South minimum is 14.3 SEER2 for split-system central AC and heat pumps. When you see both SEER and SEER2 on a label or spec sheet, use SEER2 for comparing new equipment, since that's the current standard. The same logic applies: higher SEER2 means better efficiency and lower running cost.
Size Your AC Before You Compare SEER
Efficiency (SEER) matters most when the system is correctly sized. Use our free BTU calculator to estimate the cooling capacity you need for your room or home—then compare SEER and SEER2 ratings among units in that size range to balance upfront cost and long-term savings.
Use the BTU CalculatorNext Steps
Use SEER and SEER2 as a filter when comparing central AC and heat pumps: meet the minimum for your region, then go as high as your budget allows for lower bills. Run our BTU calculator to get a cooling capacity range for your space, then ask contractors for quotes that include both size (tons/BTU) and efficiency (SEER2). A properly sized, higher-SEER system will keep you comfortable while reducing electricity use and cost for the life of the unit.