If you’re shopping in 2025 and beyond, you’ll see both SEER and SEER2 referenced in brochures and online tools. That’s because the underlying test procedure for rating air conditioners changed in the United States, and those changes ripple into the Canadian equipment market.
SEER2—Seasonal Energy Efficiency Ratio 2—is a newer, test‑based metric that uses updated U.S. Department of Energy “M1” procedures. The SEER2 technical overview explains that the new tests dramatically increase the external static pressure (the resistance the fan must push air against) by a factor of five compared with the old SEER tests, specifically to better reflect real‑world ductwork and installation conditions, as explained in the SEER2 program’s About page. Because the test is tougher, the numeric SEER2 rating for the same piece of equipment will usually be lower than its legacy SEER rating, even though the actual efficiency of the hardware hasn’t changed.
The same source notes that starting January 1, 2023, all new central air conditioners and heat pumps sold in the U.S. have to comply with these M1‑tested efficiency requirements, prompting manufacturers to redesign coils, fans, and matched air handlers, as described on the SEER2 program’s About page. For Canadian homeowners, the implication is straightforward:
There isn’t a single exact conversion between SEER and SEER2 because it depends on the specific system, but for typical residential central AC and heat pumps, industry comparisons often show SEER2 ratings landing roughly 4–7% lower than their SEER equivalents. The important thing for homeowners is the pattern, not the precise mapping:
These ranges are illustrative, not regulatory; always rely on the manufacturer’s published SEER and SEER2 values for any specific model.
When comparing two new systems side by side, make sure you’re looking at the same rating scale (SEER vs SEER2). If one quote lists SEER2 and another lists SEER, ask your contractor to provide the matching rating so you’re not comparing apples and oranges.
