SEER2 vs HSPF2 Explained: Heat Pump Efficiency Ratings

The quick answer

A heat pump does two jobs, and it has a separate efficiency rating for each:

• SEER2 (Seasonal Energy Efficiency Ratio 2) rates how efficiently it cools over a season. Higher is better.
• HSPF2 (Heating Seasonal Performance Factor 2) rates how efficiently it heats over a season. Higher is better.

You'll also see EER2 (efficiency at a single hot temperature) and COP (a real-time efficiency multiple). The ‘2’ in SEER2 and HSPF2 means the rating uses the updated 2023 US test procedure. Both numbers matter because a heat pump that cools brilliantly might heat only adequately, or vice versa. Aim for strong numbers on the rating that matches your climate's bigger job.

What changed in 2023: SEER became SEER2

In January 2023, the US Department of Energy updated the test procedures for residential HVAC efficiency, replacing SEER, EER and HSPF with SEER2, EER2 and HSPF2. The key change was raising the ‘external static pressure’ used in testing — essentially testing the equipment against the more realistic airflow resistance of real-world duct systems.

Because the new tests are tougher, the new numbers are slightly lower than the old ones for the same equipment. As a rough conversion, SEER2 is about 4.5% lower than the old SEER, and HSPF2 about 8–9% lower than HSPF. So a unit once rated 15 SEER is roughly 14.3 SEER2 — the equipment didn't get worse, the yardstick got stricter. Don't compare an old SEER number against a new SEER2 number directly.

SEER2: cooling efficiency

SEER2 measures cooling output (in BTUs) divided by the electricity used (in watt-hours) across a simulated cooling season that includes a realistic mix of temperatures. A higher SEER2 means the unit delivers more cooling per unit of electricity, lowering your summer bills.

Federal minimums vary by region (the South and Southwest require higher minimums than the North because they cool more), but as of 2023 the floor is around 13.4–14.3 SEER2 depending on region and equipment type. High-efficiency units reach the high teens to low twenties. If you live in a hot, cooling-dominated climate, SEER2 is the number to prioritize.

HSPF2: heating efficiency

HSPF2 measures total seasonal heating output divided by total electricity used over a heating season. It captures the reality that a heat pump's efficiency falls as the outside air gets colder, so it's the single best summary number for heating performance.

Current federal minimums sit around 6.7–7.5 HSPF2 depending on region and equipment, while high-efficiency cold-climate units reach 8.1, 9, or higher. In a heating-dominated climate — the Northeast, Mountain West, Upper Midwest — HSPF2 is the rating that most affects your annual bills, so weight it heavily and pair it with a check of capacity at 5°F (see our cold-climate guide).

EER2: efficiency on the hottest day

While SEER2 averages efficiency across a season, EER2 measures it at a single high outdoor temperature (95°F). It answers a different question: how efficiently does the unit cool when it's working hardest, on a brutally hot afternoon?

EER2 matters most in very hot, dry climates — Arizona, Nevada, inland California — where peak-day performance and peak electricity rates make hot-weather efficiency especially valuable. Some utility rebate programs in these regions specify a minimum EER2. For most of the country, SEER2 is the more relevant cooling number, but desert-climate homeowners should check EER2 too.

COP: the real-time efficiency multiple

COP (Coefficient of Performance) is the most intuitive efficiency measure: it's the ratio of heat energy delivered to electrical energy consumed at a given moment. A COP of 3 means the heat pump delivers 3 units of heat for every 1 unit of electricity — 300% efficiency, which is why heat pumps beat any fuel-burning system that can never exceed 100%.

COP varies with temperature: a good air-source heat pump might run at COP 3.5–4 in mild weather and COP 2–2.5 near freezing; geothermal units hold COP 4–5 year-round thanks to stable ground temperatures. HSPF2 is essentially a seasonal average of COP, expressed in the US testing format. When you see a manufacturer quote COP at low temperatures, that's a direct read on cold-climate capability.

What counts as a good number in 2026

Here's a practical cheat sheet for shopping:

As a rule of thumb, aim for at least SEER2 16 and HSPF2 8.1 for a quality high-efficiency unit. Going higher cuts running costs further but adds upfront cost — the sweet spot depends on your climate and electricity rates.

Why you need both numbers

A common mistake is fixating on one rating. A unit can have an impressive SEER2 but a mediocre HSPF2, which is fine in Florida but a poor choice in Maine. The reverse is also true. Because a heat pump heats and cools, you should evaluate both numbers against how hard each job is in your climate.

In a cooling-dominated South, weight SEER2 (and EER2) more heavily; in a heating-dominated North, prioritize HSPF2 and low-temperature capacity. In a mixed climate, look for a balanced unit strong on both. Don't let a single headline number sell you a heat pump that's optimized for the wrong season.

How ratings translate to running cost

The efficiency difference is real money over a 15–20 year life. Moving from a federal-minimum unit to a high-efficiency one can cut heating and cooling electricity use by 15–30%, depending on how much you run the system. In a high-rate state or a demanding climate, that can be hundreds of dollars a year.

But efficiency has diminishing returns: the jump from minimum to mid-tier saves the most per dollar of extra equipment cost; the jump from high-efficiency to ultra-premium saves less and costs more. The right target balances your climate, your electricity rate, and how long you'll own the home. Model the impact with the Heat Pump Savings Calculator.

Matching ratings to your climate

Use this quick guide to set your targets:

• Hot South / Southwest: prioritize SEER2 18+ and a strong EER2; HSPF2 of 7.8–8.1 is usually plenty for the mild heating season.
• Mixed mid-latitude: balanced SEER2 16–18 and HSPF2 8.1–9.
• Cold North: prioritize HSPF2 9+ and confirm capacity at 5°F on the NEEP list; SEER2 16 is fine for the shorter cooling season.

The ratings are seasonal averages for an ‘average’ US climate, so always cross-check the manufacturer's low-temperature performance data if you're in a cold region — the headline HSPF2 alone won't tell you how the unit behaves at -5°F.

How ratings tie to the federal tax credit

Efficiency ratings aren't just about running cost — they determine whether your heat pump qualifies for the 30% federal tax credit. The 25C credit (30% up to $2,000) requires the unit to meet the CEE highest-efficiency tier for your region, which is defined using SEER2, EER2 and HSPF2 thresholds.

So a unit that's merely ENERGY STAR may not qualify for the credit if it falls short of the CEE top tier in your region. Always ask your installer to confirm the specific model meets the CEE tier required for the credit, and keep the manufacturer's certification statement. We cover the credit rules in the heat pump tax credit guide.

Rated vs real-world performance

Lab ratings are standardized so you can compare models fairly, but your real-world efficiency depends heavily on installation and home factors the ratings can't capture: correct sizing, proper refrigerant charge, sealed and insulated ducts, adequate airflow, and a well-insulated home. A high-SEER2 unit installed poorly can underperform a modest unit installed well.

This is the same lesson as choosing a brand — the rating sets the ceiling, but the installer determines how close you get to it. Treat SEER2 and HSPF2 as necessary comparison tools, not guarantees, and invest in a quality installation (load calculation, duct sealing, correct charge) to actually realize the efficiency you paid for.

The cost-versus-efficiency tradeoff

Higher ratings cost more upfront, so the question is how much efficiency to buy. A useful framework: estimate the annual running-cost saving from a higher tier, compare it to the extra equipment cost, and look at the simple payback. In a high-rate state with a demanding climate, paying up for SEER2 18 / HSPF2 9 can pay back in a handful of years; in a mild climate with cheap power, the premium tier may never pay back.

Also weigh comfort: higher-efficiency units almost always use variable-speed inverter compressors, which deliver steadier temperatures, better humidity control and quieter operation — benefits beyond the energy savings. For many buyers those comfort gains justify a mid-to-high tier even when the pure payback is modest.

How to use these numbers when shopping

Put it all together with a simple shopping routine:

1. Set targets for your climate — e.g., SEER2 18+/EER2 strong in the hot South; HSPF2 9+ and good 5°F capacity in the cold North.
2. Confirm CEE-tier eligibility for the 30% credit on the specific model.
3. Compare SEER2 and HSPF2 together, not in isolation.
4. Insist on a quality installation so you actually achieve the rated numbers.