FU 202 · Guide
SEER2 explained
SEER2 is the number that tells you how much electricity an air conditioner or heat pump uses to cool your home. Here is what it measures, why the numbers changed in 2023, and how to use it when you compare systems.
Fortress Cooling & Heating · Updated October 19, 2026
What SEER2 measures
SEER2 stands for Seasonal Energy Efficiency Ratio 2. It is the cooling a system delivers over a typical cooling season, measured in BTUs, divided by the electricity it uses, measured in watt-hours.
Higher is more efficient. Electricity use falls in proportion to the rating: a 20 SEER2 system uses half the electricity of a 10 SEER2 system to deliver the same cooling.
Why the numbers changed in 2023
Until 2023 systems were rated in SEER. On January 1, 2023, the U.S. Department of Energy switched to a new test, and the ratings became SEER2. The new test pushes air through the system against more resistance (0.5 inches of water column instead of 0.1), which is closer to how air moves through real ductwork in a real home.
The equipment didn't get worse. The test got tougher, so the same system scores lower. As a rough guide, a SEER2 rating is about 5 percent lower than the old SEER rating for the same equipment.
| Old SEER rating | About the same as |
|---|---|
| 14 SEER | 13.4 SEER2 |
| 15 SEER | 14.3 SEER2 |
| 16 SEER | 15.2 SEER2 |
| 18 SEER | 17.1 SEER2 |
| 20 SEER | 19.0 SEER2 |
These are approximations. Each system is tested on its own, so for an exact figure, look up the rating for that specific combination of outdoor and indoor equipment.
The minimum in Arizona
Arizona is in the Department of Energy's Southwest region, which has the strictest standard for air conditioners. A new split air conditioner installed here since January 1, 2023 must be rated at least:
- 14.3 SEER2 for systems under 45,000 BTU per hour (most homes).
- 13.8 SEER2 for larger systems.
Arizona also sets a minimum EER2, which is explained below. If your current system was installed well before 2023, it may be rated far below today's minimum.
The other ratings you'll see
| Rating | What it measures | Found on |
|---|---|---|
| SEER2 | Cooling efficiency over a whole season. Higher is better. | Air conditioners, heat pumps |
| EER2 | Cooling efficiency at one hot moment: 95° outside. It matters here, because Valley afternoons run well past that. | Air conditioners, heat pumps |
| HSPF2 | Heating efficiency over a season. Higher is better. | Heat pumps |
| AFUE | The share of the gas a furnace turns into heat. A 96% AFUE furnace turns 96% of its fuel into heat. | Gas furnaces |
Reading the yellow EnergyGuide label
New air conditioners and heat pumps come with a yellow EnergyGuide label. It shows the system's SEER2 and EER2 ratings, where they fall among similar models, and a map of the regional standards. If the label is gone, the model numbers on the outdoor unit and the indoor coil or air handler identify the system, and the AHRI Directory lists the rating for that pair.
A rating belongs to a matched system, not to the outdoor unit alone. The same outdoor unit can carry different ratings depending on the indoor coil or air handler it's paired with. When a brochure says "up to," that's the best pairing.
How high should you go?
There's no single right number. It depends on a few things:
- How long you'll stay. The longer you're in the home, the more seasons the extra efficiency has to pay you back.
- How hard your home works its AC. West-facing rooms, big windows, and older insulation all add run time.
- Comfort and noise. Higher-rated systems are usually two-stage or variable-speed. They run longer at lower speed, which keeps temperatures steadier, pulls more humidity out of the air, and runs more quietly.
- Budget. Every step up costs more up front. The question is whether the savings and comfort are worth it to you.
Our proposals line these up for you: Essential Comfort is a single-stage system, Preferred Comfort is two-stage, and Signature Comfort is variable-speed. To put dollar figures on the difference, run your numbers in the SEER savings calculator, then compare real models in Lennox products.
Common questions
Is a 14.3 SEER2 system worse than a 15 SEER system?
No. They are about the same. SEER2 uses a tougher test, so the same equipment scores roughly 5 percent lower in SEER2 than it did in SEER.
Where do I find my system’s SEER rating?
Check the yellow EnergyGuide label if it is still on the outdoor unit, or the model numbers on the nameplates of the outdoor unit and the indoor coil or air handler. The rating belongs to the matched pair, and the AHRI Directory lists it by model number. We can look it up at a visit.
Does a higher SEER2 rating always mean a lower bill?
For the same home, the same thermostat settings and a correctly sized system, a higher rating means less electricity for the same cooling. Leaky ducts, an oversized system or a poor installation can erase the difference, which is why the installation matters as much as the rating.