SEER2 measures how efficiently an air conditioner or heat pump cools over a season, EER2 measures cooling efficiency at a fixed hot-day condition, and HSPF2 measures how efficiently a heat pump heats over a season; higher is better in each, the “2” versions replaced the older SEER/EER/HSPF in 2023 with a tougher test that lowered the numbers for the same equipment by roughly 4–5%, and the current federal minimum for split-system air conditioners in the Southeast is 14.3 SEER2 (13.8 for larger systems), with heat pumps at 14.3 SEER2 and 7.5 HSPF2 nationwide. In North Carolina’s long cooling season a step up from minimum to the mid-tier usually pays for itself; the top tier is bought for comfort and quiet more than for payback.
The three ratings
SEER2 (Seasonal Energy Efficiency Ratio 2) is total cooling delivered over a season divided by total electricity used, under a standardised test. It’s the headline number on AC and heat pump labels.
EER2 (Energy Efficiency Ratio 2) is the same ratio measured at a single hot condition (95°F outdoors). It tells you how the system performs on the worst days, which matters more in hot-dry climates than in ours, but it’s a useful check that a high SEER2 unit isn’t only efficient in mild weather.
HSPF2 (Heating Seasonal Performance Factor 2) is the heating equivalent for heat pumps: heat delivered over a season divided by electricity used. For a North Carolina heat pump, this number determines your winter bill as much as SEER2 determines your summer one.
SEER vs SEER2
Since January 2023 equipment has been rated under the “2” procedures, which test at higher external static pressure to better reflect real ductwork. Same equipment, lower number: roughly 16 SEER ≈ 15.2 SEER2, 18 SEER ≈ 17 SEER2, 20 SEER ≈ 19 SEER2. When comparing an old system’s rating to a quote, convert; when comparing quotes, make sure they’re all quoting SEER2.
Current minimums (Southeast)
Split-system AC: 14.3 SEER2 (under 45,000 BTU/hr) and 13.8 SEER2 (45,000 and above), with an EER2 floor. Heat pumps: 14.3 SEER2 and 7.5 HSPF2 nationwide. Anything on the market meets these; the question is how far above them to go.
What a higher rating saves
Roughly, cooling energy scales inversely with SEER2: moving from 14.3 to 16 SEER2 cuts cooling electricity by about 10%, from 14.3 to 18 by about 20%, and to 20 by about 28%. For a North Carolina home spending $700–$1,000 a year on cooling, that’s roughly $70–$100, $140–$200 and $200–$280 a year respectively. Against typical equipment premiums (mid-tier a few thousand dollars, top tier several thousand more), the mid-tier step usually pays back within the system’s life and the top tier often doesn’t on energy alone. HSPF2 works the same way for heating: 7.5 to 8.5 is roughly a 12% heating saving; to 9.5 roughly 21%.
What the rating doesn’t tell you
Installation quality can cost you more efficiency than the rating difference between tiers: a 17 SEER2 system with an undercharge and leaky ducts underperforms a well-installed 15.2. Sizing matters more than rating for comfort (sizing). And the top-tier systems are usually variable-speed, whose real selling point in our climate is humidity control and quiet operation, not the SEER2 number (variable-speed systems).
Ratings and rebates
Utility rebates and Energy Saver NC set efficiency thresholds (often around ENERGY STAR levels, e.g., mid-teens SEER2 and 8+ HSPF2 for heat pumps); a system just below a threshold can cost more net than one just above it. Check the current thresholds before choosing a tier: how the incentives stack. Current installed prices by tier are on the AC replacement cost and heat pump cost pages, and every contractor on the North Carolina registry shows the license status we found.