SEER Rating Explained: SEER vs SEER2 and What an Upgrade Saves

What SEER and SEER2 measure

SEER stands for Seasonal Energy Efficiency Ratio. It is the total cooling an air conditioner or heat pump delivers over a modeled cooling season, divided by the electricity it uses over that same season. A higher number means more cooling per kilowatt-hour.

SEER = seasonal cooling output (BTU) ÷ seasonal electricity input (Wh)

The seasonal part matters. The rating is not a single snapshot at one temperature. The test runs the unit at several outdoor temperatures and weights the results toward the mild 80–85 °F hours that make up most of a real summer. That is why a two-stage or variable-speed system can post a very high SEER: it runs at low capacity most of the time, where compressors are most efficient. For a single hot-afternoon number, look at EER and EER2 instead.

Why SEER2 replaced SEER in 2023

From January 1, 2023, the US Department of Energy moved to a revised test procedure (called M1). The headline change is external static pressure: the old test assumed ductwork that barely resisted airflow (around 0.1 in. w.c.), while the new one uses about 0.5 in. w.c., which is much closer to a real duct system with a filter, coil and registers. The blower works harder, so the same equipment earns a lower number.

As a working conversion, multiply SEER by about 0.95 to get SEER2. DOE's own equivalences run slightly higher (a factor closer to 0.955), which is why the old 14 SEER floor became 13.4 SEER2 rather than 13.3.

A SEER2 label does not mean a new unit is worse than an old one with a bigger SEER number on its sticker. It means the ruler changed. Always compare like with like.

2023 DOE regional minimums

Federal minimums for central air conditioners and heat pumps depend on where the equipment is installed. The South has higher floors because cooling runs so many more hours there.

In the Southwest, split air conditioners must also meet a full-load EER2 floor (11.7 EER2 below 45,000 BTU/h and 11.2 EER2 above, relaxed for units rated 15.2 SEER2 or higher). Packaged single-cabinet units have their own minimums, currently 13.4 SEER2 nationally. In the southern regions the rule is enforced by installation date, so a contractor cannot install leftover stock that falls below the regional minimum. Heat pump heating ratings are covered on the HSPF2 page.

The savings formula and a worked example

To estimate cooling electricity, divide the seasonal cooling you need by the efficiency rating. Using full-load cooling hours keeps the math honest: it is the number of hours the system would have to run at full capacity to deliver a whole season's cooling.

Annual kWh = Capacity (BTU/h) × Full-load hours ÷ (SEER2 × 1,000)
Old SEER2 ≈ Old SEER × 0.95
Savings ($) = (Old kWh − New kWh) × Rate ($/kWh)
Simple payback (years) = Upgrade cost ÷ Annual savings

Example with the calculator defaults: a 3-ton (36,000 BTU/h) system running 1,500 full-load hours needs 54,000,000 BTU of cooling a year.

• Old 10 SEER unit ≈ 9.5 SEER2: 54,000,000 ÷ 9,500 = 5,684 kWh, or about $966 at $0.17/kWh.
• New 15.2 SEER2 unit: 54,000,000 ÷ 15,200 = 3,553 kWh, or about $604.
• Difference: about 2,132 kWh and $362 a year.
• Payback: the upgrade cost defaults to 0, so the calculator shows n/a. Enter $3,000 and it returns 3,000 ÷ 362 ≈ 8.3 years.

Payback also shows n/a when the new rating is no better than the old one, since there are no savings to divide by.

Use your own rate from a recent bill (total charges divided by kWh gives an all-in figure). To check what one hour or one month costs instead of a whole season, try the AC running cost calculator.

Is a higher SEER2 worth paying for?

Each step up the SEER2 ladder saves less than the one before, because you are dividing by a bigger number. For the same 3-ton, 1,500-hour example at $0.17/kWh:

Going from 14.3 to 16 SEER2 saves roughly $70 a year here; in Phoenix, with twice the hours, it saves twice that. Divide the price difference between two quotes by the yearly savings to get a simple payback period, and compare it with a realistic equipment life (see how long AC units last). Higher-tier systems also bring quieter operation and better humidity control, which can matter more than the dollars.

The rating only applies to the exact outdoor unit, indoor coil and furnace or air handler combination listed in the AHRI directory. Ask your contractor for the AHRI reference number of the matched system they are quoting.

Why real-world efficiency falls short of the label

• Sizing: an oversized unit short cycles and never settles into efficient steady running. Check the size with the AC tonnage calculator.
• Refrigerant charge: an under- or over-charged system can lose 10–20% of its capacity and efficiency. Charge should be verified by an EPA 608 certified technician using superheat and subcooling, not by topping up.
• Airflow and ducts: clogged filters, undersized returns and leaky attic ducts all cut delivered efficiency, regardless of the label.
• Dirty coils: a matted condenser coil raises head pressure and power draw. Rinse it gently each spring with the power off.

Frequently asked questions