On 1 January 2023 the US Department of Energy changed the test procedure for residential air conditioners and heat pumps. The efficiency metrics gained a "2".
What changed
The old tests were run at an assumed external static pressure of 0.1 inches of water column — a figure that corresponds to almost no ductwork at all.
The new procedure raises that to 0.5 in. w.c. for typical ducted systems, which is far closer to what a real house presents to a blower.
Pushing air against more resistance takes more fan power, so the same physical equipment produces a lower efficiency number under the new test.
The conversion
Approximate, and it varies by equipment type:
| Old | New |
|---|---|
| SEER | ≈ SEER × 0.95 |
| EER | ≈ EER × 0.95 |
| HSPF | ≈ HSPF × 0.85 |
So 16 SEER becomes roughly 15.2 SEER2, and 14 SEER becomes about 13.4 SEER2.
Ductless and mini-split equipment is tested at lower static pressure and is affected much less, which is part of why mini-split SEER2 numbers look so strong beside ducted equipment.
What each metric measures
SEER2 — cooling efficiency over an entire season, averaging across a range of outdoor temperatures. The number most quoted.
EER2 — cooling efficiency at a single hot operating point, 95°F outdoor. More relevant in hot dry climates where the system spends its life near design conditions.
HSPF2 — heating efficiency of a heat pump over a season.
COP — instantaneous heating efficiency, useful for comparing performance at a specific low outdoor temperature.
A unit with a high SEER2 and a modest EER2 does well in a mixed climate with mild average conditions and less well in a place with a long stretch of 105°F afternoons.
Regional minimums
Minimum efficiency is set regionally rather than nationally, and the South and Southwest carry higher minimums than the North because cooling hours dominate there.
There is also an enforcement difference worth knowing: in the Southeast and Southwest the standard applies at installation, not at manufacture, so a distributor cannot legally sell remaining lower-efficiency stock into those regions.
Whether a higher number is worth the money
The savings from a higher rating scale with how many hours the system runs. In Phoenix or Houston the run hours are enormous and an efficiency step pays back; in a mild climate with a short cooling season the same step may not pay back within the equipment life.
Three things frequently matter more than the rating:
Correct sizing, because an oversized high-SEER2 system underperforms a correctly sized modest one.
Duct sealing and insulation, because leaky attic ducts waste a larger fraction than any rating difference recovers.
Installation quality — refrigerant charge and airflow. Field studies consistently find a large share of installations operating well below rated efficiency for these reasons alone.
Reading a quote
Two quotes citing different metrics are not comparable. Ask for SEER2 on both, and for the AHRI certified reference number for the specific combination of outdoor unit, indoor coil and air handler.
That last point matters: the rating belongs to the matched system, not to the condenser. An efficient outdoor unit paired with an old indoor coil does not deliver the rated performance, and the AHRI number is what proves the combination was actually tested.
Tax credits and rebates track the new numbers
Federal and utility incentive programmes were rewritten around SEER2, EER2 and HSPF2 thresholds, and the qualifying levels are stated in the new units.
That means a unit marketed with an old SEER figure may sit below a threshold its number appears to clear. Check the qualification against the certificate rather than against the brochure, and check it for the matched system rather than the outdoor unit alone.
Programme thresholds also change from year to year, so a model that qualified last season may not this season.
What the label does not tell you
Neither rating captures how the equipment behaves at part load in a humid climate, and that is where most of the discomfort in a house comes from.
A variable-capacity system that modulates down to 30% of its rating will dehumidify far better than a single-stage unit of identical SEER2, because it runs longer at lower output. The seasonal number cannot express that difference, and in the Southeast it is often the more important property.