- One formula sets every savings claim:
new cost = current cost × (current rating ÷ new rating). - Convert before comparing: nameplate SEER × 0.95 ≈ SEER2; HSPF × 0.85 ≈ HSPF2 (2023 DOE test procedure, split systems).
- 2026 federal minimums: 13.4 SEER2 (North) / 14.3 SEER2 (South & Southwest); 15–16 SEER2 is the value sweet spot for most homes.
- Worked examples: SEER2 9 → 16.5 cuts cooling energy ~45%; AFUE 80% → 96% cuts gas use ~17%.
The one formula behind every savings claim
Heating and cooling energy cost scales inversely with efficiency. Whatever your current system costs to run, a new one costs:
Go from an effective SEER2 of 9 to a new 16.5 SEER2 unit and cooling energy drops to 9 ÷ 16.5 ≈ 55% of today's — a 45% cut. From an 80% AFUE furnace to 96%, gas use falls to 80 ÷ 96 ≈ 83% — a 17% cut. The ratio is the whole story; everything else (climate, rates, hours) just sets how many dollars the percentage applies to.
The three ratings
| Rating | Applies to | Measures | Typical range |
|---|---|---|---|
| SEER2 | AC & heat pump cooling | Cooling delivered per unit of electricity over a season (BTU/Wh) | 13.4 (2023 minimum, North) to 20+ (premium) |
| EER2 | AC & heat pump cooling | Same, but at a single hot-day condition (95°F) — matters most in desert climates | ~9–14 |
| HSPF2 | Heat pump heating | Heat delivered per unit of electricity over a heating season (BTU/Wh) | 7.5 (minimum) to 10+ (cold-climate models) |
| AFUE | Gas furnaces | Share of the fuel's energy that becomes heat in the home | 80% (standard) or 90–98.5% (condensing) |
SEER vs. SEER2 — why the numbers changed in 2023
In 2023 the Department of Energy replaced SEER with SEER2, tested under higher external static pressure that better matches real ductwork. Same machine, tougher test: a nameplate SEER converts to SEER2 at roughly ×0.95 for split systems (HSPF to HSPF2 at roughly ×0.85). So a SEER 14 unit is about 13.3 SEER2. When comparing your old unit to new quotes, convert first — otherwise you'll understate the upgrade by comparing a flattering old test to a strict new one. Our calculators do this conversion automatically.
What a rating can't tell you
Ratings are lab seasonal averages. Three things move real-world results: installation quality (refrigerant charge, airflow, and duct sealing can cost 10–25% of rated efficiency — the best unit badly installed underperforms a mid-tier unit done right); sizing (oversized systems short-cycle, losing efficiency and dehumidification — insist on a Manual J load calculation, not a rule of thumb); and climate match (dry-heat climates should weight EER2; cold climates should look at a heat pump's capacity and COP at 5°F, not just HSPF2).
Is a higher tier worth it? Diminishing returns, quantified
Because savings follow the ratio, each step up saves less than the one before. From SEER2 9 to 15.2 cuts cooling energy ~41%; 15.2 to 17.5 cuts only ~13 points more; 17.5 to 20 adds ~7. Premium tiers often carry price jumps that outrun those slices — except where variable-speed comfort, humidity control, or rebate tiers change the equation. This is exactly what the calculators' side-by-side option cards are for: put the actual quotes in and let the payback years rank themselves.
Frequently asked questions
What is a good SEER2 rating in 2026?
The federal minimum is 13.4 SEER2 (North) or 14.3 (South/Southwest). 15–16 SEER2 is the value sweet spot for most homes; 17–20+ makes sense in hot climates, high-rate areas, or where rebates target premium tiers. The right answer is the tier whose payback fits your horizon — run your numbers.
How do I convert SEER to SEER2?
For common split systems, multiply SEER by about 0.95 (SEER 14 ≈ 13.3 SEER2). HSPF converts to HSPF2 at about ×0.85. Package units use slightly different factors. It's an approximation of the stricter 2023 test procedure, good enough for savings math.
Is a 96% furnace worth it over an 80% one?
Gas use falls by the ratio 80÷96, about 17%. Worth it depends on your heating load and gas price: at 900 therms/yr and $1.50/therm that's ~$225/yr against a price premium of $1,500–$3,000 — often a reasonable payback in cold climates, rarely in mild ones. Condensing furnaces also need a condensate drain and new venting, which is part of the quote.
Does HSPF2 tell me if a heat pump works in cold climates?
Only partly. HSPF2 is a seasonal average on a national profile. For cold climates, check the unit's rated heating capacity and COP at 17°F and 5°F (cold-climate models hold 70–100% of capacity at 5°F) and how backup heat is handled. ENERGY STAR's cold-climate designation is a useful screen.