Is SEER2 better or worse than SEER?

Neither — it is a more realistic test. SEER2 uses a higher test static pressure (about 0.5 vs 0.1 inches of water), so the resulting number is lower for the same equipment. Roughly, SEER2 ≈ SEER × 0.95.

How do I convert SEER2 to EER?

Use the documented approximation EER ≈ SEER × 0.9. It converts a seasonal rating into a single-point efficiency for peak running-cost math. It is an estimate, not an exact identity.

Should I always buy the highest SEER2 available?

Not necessarily. A higher SEER2 costs more up front and only pays back if you run the unit enough hours. In mild climates the payback can be very long. Estimate it with your own energy rate before deciding.

Why does a variable-speed unit have such a high SEER2?

Because SEER2 is a seasonal blend that includes many light part-load hours, and variable-speed (inverter) equipment is far more efficient when it throttles down to match a small load than when it runs flat out. Single-point EER, measured at full load on a hot day, does not capture that advantage, so a premium variable-speed unit can show a spectacular SEER2 alongside a more ordinary EER. In a hot climate that keeps the unit near full load, weight the EER accordingly.

SEER vs SEER2 explained

SEER2 is not a new technology — it is a new test. Understanding the difference keeps you from comparing two units on the wrong scale.

By Francesco Zinghinì

If you shopped for an air conditioner before and after 2023, you may have noticed the efficiency numbers shifted downward even though the equipment got better. That is because the U.S. Department of Energy changed the test procedure, replacing SEER with SEER2. This guide explains what the ratings measure, why the switch happened, and how to convert between SEER2 and the single-point EER used in running-cost math.

What SEER measures

SEER stands for Seasonal Energy Efficiency Ratio. It is the total cooling output over a typical cooling season (in BTU) divided by the total electrical energy consumed (in watt-hours). A higher SEER means more cooling per unit of electricity. Because it is seasonal, it blends performance across a range of outdoor temperatures rather than a single operating point — which is what makes it a realistic proxy for a full summer of use.

Why SEER2 replaced SEER

The old SEER test measured equipment against a very low external static pressure — roughly 0.1 inches of water column — that did not reflect the real ductwork most systems are attached to. Starting in 2023, the DOE 2023 test procedure (the "M1" method) raised the test static pressure to about 0.5 inches, much closer to a real home. Testing against more realistic resistance produces a lower, more honest number. As a rough rule, SEER2 ≈ SEER × 0.95 for typical split systems — so a 16 SEER unit is roughly 15.2 SEER2. The equipment did not get worse; the yardstick got more accurate. The same reform produced EER2 and HSPF2 for the same reason.

SEER2 vs EER: seasonal vs single-point

SEER2 is a seasonal average. EER (Energy Efficiency Ratio) is a single-point measurement at a fixed, hot condition (95 °F outdoors). EER is the number you want for peak-load running-cost math, because it tells you how the unit performs when it is working hardest. A documented approximation links them:

EER ≈ SEER × 0.9

So a 16 SEER2 unit behaves like roughly EER 14.4 at design conditions. This is an estimate, not an identity — the true relationship depends on the specific equipment — but it is good enough to turn a seasonal rating into a running-cost input. The EER ↔ SEER2 converter applies it both ways.

From rating to dollars

Efficiency only matters because it drives your bill. The power a unit draws is its cooling capacity divided by its efficiency: kW = capacity (BTU/h) ÷ (EER × 1,000). A 36,000 BTU/h unit at EER 12 draws 3.0 kW; the same unit at EER 14.4 draws about 2.5 kW — roughly 17% less electricity for the same cooling. Feed your own $/kWh rate into the AC running-cost calculator to see that gap in dollars, and use the SEER2 upgrade-savings tool to estimate the annual savings and payback of moving from an old unit to a new one.

Variable-speed equipment and part-load efficiency

The reason SEER2 and EER can diverge so much on modern equipment is part-load operation. Older single-stage units run flat out or not at all, so their seasonal and peak efficiencies are close. Two-stage and variable-speed (inverter) units, by contrast, can throttle down to match a light cooling load, and they are far more efficient when loafing than when sprinting. SEER2, being a seasonal blend that includes lots of part-load hours, rewards that ability with a high number; EER, measured at a single hot full-load point, does not. That is why a premium variable-speed unit might show a spectacular SEER2 but a more ordinary EER — and why, in a hot climate where the unit runs near full load most of the summer, the EER-based running cost may matter more than the headline SEER2 suggests.

The practical lesson: match the metric to your reality. In a mild climate with lots of gentle part-load hours, a high SEER2 variable-speed unit can genuinely deliver its seasonal promise. In a hot climate that pins the unit at full load, weight the EER and estimate cost at design conditions with the running-cost tool before paying for the top SEER2 tier.

Reading a spec sheet without getting fooled

Three practical rules follow from all this. First, only compare SEER2 to SEER2 (or SEER to SEER) — never mix the scales, or you will penalize the newer, more honestly rated unit. Second, remember that a higher SEER2 pays off only if you run the air conditioner enough hours to recover the price premium; in a mild climate the payback on a top-tier unit can be very long. Third, SEER2 is a cooling metric only; for heat pumps in heating mode the relevant number is HSPF2, covered in HSPF2 & COP explained. Match the rating to the season, keep the scales consistent, and let your own energy rate — not the sticker — decide how much efficiency is worth.