SEER2, AFUE, and HSPF2 explained
Every HVAC quote is studded with acronyms, and they are not interchangeable: one rates cooling, another heating, another a furnace's fuel use. Here is what SEER2, EER2, HSPF2, and AFUE mean in plain English, the current minimums, and where a higher rating is worth the money.
Key takeaways
- SEER2 rates cooling efficiency over a season for air conditioners and heat pumps; higher is better.
- EER2 rates cooling efficiency at peak conditions; it matters most in very hot climates.
- HSPF2 rates a heat pump's heating efficiency; higher is better.
- AFUE rates a furnace as the percent of fuel turned into heat; 80% is standard, 90% to 98% is high-efficiency condensing.
- The '2' versions (effective 2023) come from a tougher test, so do not compare a SEER2 number against an old SEER number.
Cooling: SEER2 and EER2
SEER2 (Seasonal Energy Efficiency Ratio 2) measures cooling efficiency across a whole season and applies to both central air conditioners and heat pumps. Higher means lower cooling bills. EER2 measures efficiency at a single peak-heat condition, so it is the number to weigh if you live where summers are brutal. As of 2023, the federal minimum SEER2 is about 13.4 in northern states and about 14.3 in the South; ENERGY STAR models sit above the minimum.
Heating: HSPF2 and AFUE
A federal rule will raise the minimum for most new gas furnaces to 95% AFUE starting in late 2028, a level today's condensing furnaces already meet.
- HSPF2: the Heating Seasonal Performance Factor 2 rates how efficiently a heat pump heats over a season. Higher is better; the current federal minimum for a split-system heat pump is 7.5.
- AFUE: Annual Fuel Utilization Efficiency rates a furnace or boiler as the percentage of fuel it turns into usable heat. An 80% AFUE furnace wastes 20% up the flue; a high-efficiency condensing furnace reaches 90% to 98%.
Why the numbers changed in 2023
You may see both old and new ratings while shopping. Starting in 2023, testing moved to a tougher procedure (the '2' in SEER2, EER2, and HSPF2) that uses higher static pressure to better mimic real home ductwork. The result: a SEER2 number is a little lower than the old SEER number for the same equipment, so never compare a SEER2 rating against an old SEER rating directly.
What's worth paying for
- In a hot climate, a higher SEER2 (and a strong EER2) pays back through lower summer bills; in a mild one, the minimum-efficiency unit may be the rational buy.
- For a heat pump in a cold climate, weigh HSPF2 and look for a cold-climate-rated model.
- For a furnace, a 90%-plus condensing unit saves fuel every winter and is where the standard is heading anyway.
- Right-sizing with a Manual J load calculation matters more than chasing the highest rating on an oversized system.
Frequently asked questions
What is a good SEER2 rating?
What does AFUE mean on a furnace?
Why is SEER2 lower than the old SEER number?
See the numbers for your town
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Cost figures in this guide are modeled national ranges for general planning, not quotes. Local pricing varies, always get an on-site assessment from a licensed pro before you commit. Evergreen guide