SEER2, HSPF2 and EER2: What Efficiency Ratings Actually Mean

Efficiency ratings answer one question: how much heating or cooling do you get per unit of electricity? SEER2 rates cooling over a simulated season, HSPF2 rates heating over a simulated season, and EER2 rates cooling at one hot, steady condition. Higher is better in every case — but in Western Washington's mild climate the heating number matters far more, and chasing the very top of the scale rarely pays for itself.

What changed in 2023 — SEER versus SEER2?

In January 2023, the U.S. Department of Energy replaced the old test procedure with the "M1" standard. The biggest change is that equipment is now tested against higher external static pressure — a fancy way of saying the test finally accounts for the resistance of real-world ductwork instead of an idealized lab setup. Same equipment, tougher test, so the numbers dropped: a unit's SEER2 rating reads a bit lower than its old SEER rating would have. HSPF became HSPF2 and EER became EER2 under the same change. The practical takeaway: never compare a SEER number to a SEER2 number directly. If you're comparing quotes or an old unit to a new one, make sure both figures use the same standard.

What does each rating actually measure?

Rating	What it measures	When it matters most
SEER2	Total cooling delivered over a simulated season divided by total electricity used — an average across mild and hot days	Long, hot cooling seasons with lots of part-load running
EER2	Cooling efficiency at one fixed, hot outdoor condition — a steady-state stress test	Sustained heat waves; peak-demand performance
HSPF2	Total heating delivered over a simulated season divided by total electricity used	Anywhere heating dominates the year — like here

A useful mental model: SEER2 is average fuel economy over a season of mixed driving; EER2 is fuel economy holding 70 on a hot day with the AC maxed.

Why does the Pacific Northwest change the math?

Most efficiency marketing is written for Phoenix and Houston, where air conditioners run brutally long seasons and every SEER2 point compounds. The South Sound is close to the opposite. Our summers have grown hotter and cooling is no longer optional, but the cooling season here is still short — a heat pump in Lakewood or Olympia spends the bulk of its annual runtime heating through our long, mild, damp winters.

That flips the priority order. HSPF2 is the number to study first, because it describes the mode your system will live in most of the year. Conveniently, our winters are gentle on heat pumps: modern units keep strong efficiency in the 35-to-50-degree weather that dominates a Puget Sound winter. It's widely accepted that a heat pump in a climate like this delivers heat using roughly a third of the electricity that electric resistance heating would need — a big reason heat pumps have become so popular across Pierce, King, and Thurston counties.

Where do diminishing returns kick in?

Each step up the efficiency ladder saves less than the one before it, because the savings apply to a shrinking energy bill. Moving from an old, worn-out system to a modern mid-efficiency heat pump captures most of the available savings; moving from mid-tier to top-tier captures a much smaller slice — and in a short cooling season like ours, ultra-high SEER2 has limited runway to pay you back. Top-tier equipment often earns its keep through comfort features (variable-speed operation, quieter running, better humidity control) rather than raw efficiency arithmetic. Buy those features because you want them, not because the SEER2 badge is bigger.

Do ratings affect rebates?

Yes — most utility and government incentive programs set minimum SEER2, EER2, or HSPF2 floors that equipment must meet to qualify, and some tiers step up with efficiency or cold-climate certification. Those thresholds change program to program and year to year, so verify current requirements before you buy.

Picking the right number for your house

The right efficiency tier depends on your home's heat loss, your ductwork, your utility's incentives, and how long you plan to stay. A heat pump consultation can run those numbers for your actual house — not a Phoenix marketing brochure — and show where the sensible stopping point is.