The short answer
In Phoenix, the federal minimum for a new split-system AC is 14.3 SEER2, but 15.2 SEER2 or higher is the practical target — it's the threshold for the SRP Cool Cash rebate and meaningfully lower summer bills. Because of our extreme heat, the EER2 rating matters just as much as SEER2.
What do SEER2 and EER2 actually mean?
SEER2 (Seasonal Energy Efficiency Ratio 2) measures how efficiently a system cools across a whole season — an average. EER2 measures efficiency at a single hot temperature (95°F). Both are higher-is-better.
For Phoenix, EER2 deserves extra attention: we spend so much of the year near or above 95°F that a system's hot-day performance (EER2) reflects real life here better than the seasonal average. A great SEER2 with a mediocre EER2 can disappoint on a 115° afternoon.
What's the minimum SEER2 allowed in Arizona?
As of 2023, the federal minimum for new split-system central ACs under 45,000 BTU in the hot-dry Southwest region — which includes Arizona — is 14.3 SEER2. You can't legally install a brand-new system below that here.
So 14.3 SEER2 is the floor, not a recommendation. The real question is how far above the floor it's worth going.
What SEER2 should you actually buy?
For most Phoenix homes, the sweet spot lands like this:
- 14.3 SEER2 — the minimum; lowest up-front cost, but doesn't qualify for SRP Cool Cash and costs more to run
- 15.2 SEER2 — the practical target; qualifies for SRP Cool Cash and noticeably lowers summer bills
- 16–18+ SEER2 — premium efficiency; biggest bill savings and best comfort, higher up-front cost; worth it for long stays and heavy use
Why 15.2 is the magic number
SRP's Cool Cash rebate requires 15.2 SEER2 or higher. Stepping from 14.3 to 15.2 unlocks the rebate and lowers your bills — often the best value tier for SRP customers.
Does higher SEER2 pay off in the desert?
Because Phoenix systems run so many hours, efficiency gains compound faster here than almost anywhere — more cooling hours means more chances to save. A higher-efficiency system can return its premium through lower SRP/APS bills over its life, especially if you'll stay in the home a while.
But efficiency only delivers if the system is correctly sized and installed. A high-SEER2 unit that's oversized or poorly installed underperforms — which is why we cover sizing and whether higher SEER2 is worth it in companion guides.
It's the legal minimum and will cool your home, but it won't qualify for the SRP Cool Cash rebate and will cost more to run than a 15.2+ system over a desert summer. For most Phoenix homeowners, 15.2 SEER2 is the better value once the rebate and bill savings are factored in.
Both — but pay extra attention to EER2 here. EER2 reflects performance at 95°F, which is closer to a typical Phoenix afternoon than the seasonal SEER2 average. A balanced system has strong numbers on both.
Terms in this guide
- SEER2
- Seasonal Energy Efficiency Ratio 2 — the current rating for how efficiently a central AC or heat pump cools over a season. Higher is more efficient. As of 2023 the federal minimum for new split-system ACs in the hot-dry Southwest (including Arizona) is 14.3 SEER2; SRP's Cool Cash rebate requires 15.2 SEER2 or higher.
- EER2
- Energy Efficiency Ratio 2 — efficiency measured at a single high outdoor temperature (95°F). Because Phoenix spends so much of the year near or above that mark, EER2 is arguably a more honest efficiency number for the desert than the seasonal SEER2 average.
- SRP Cool Cash
- Salt River Project's rebate for SRP electric customers who install qualifying high-efficiency equipment (15.2 SEER2 or higher). It pays up to $1,125, with an additional variable amount based on system tonnage, for installs completed by April 30, 2027. RM III files the paperwork for you.
- AHRI-matched system
- An outdoor and indoor unit certified by the Air-Conditioning, Heating, and Refrigeration Institute to perform together at their rated efficiency. Rebates and warranties generally require an AHRI-matched system — mixing mismatched parts can void both.
- Ton (of cooling)
- A measure of an air conditioner's cooling capacity. One ton equals 12,000 BTU/hour of heat removal. Phoenix homes are commonly sized around 1 ton per 400–600 square feet, but the only correct way to size a system is a Manual J load calculation — not a rule of thumb.