Residential HVAC Ratings explained
SEER, SEER2, HSPF2, AFUE — What the Numbers Mean
Four ratings. One rule: higher means more efficient. Here's which applies to which equipment.
The Four Ratings
SEER2 — Cooling efficiency for AC units and heat pumps. The current standard as of 2023. Higher = less electricity per degree of cooling. Think of it as MPG for your air conditioner.
HSPF2 — Heating efficiency for heat pumps only. Does not apply to gas furnaces. Same concept as SEER2 but for the heating season.
AFUE — Gas furnace efficiency, expressed as a percentage. 80% AFUE means 80 cents of every gas dollar becomes heat. 20 cents exits the flue.
SEER — The old cooling standard, replaced by SEER2 in January 2023. Still on existing equipment. Subtract roughly 5% to compare fairly against a SEER2 quote.
Why the "2" Was Added
In 2023, the Department of Energy updated the testing method for air conditioners and heat pumps. The new test simulates higher resistance in real ductwork — so the ratings are roughly 5% lower than the old numbers for equivalent equipment. The equipment didn't get worse. The test got more honest.
A 16 SEER unit is roughly equivalent to a 15.2 SEER2 — not a 16 SEER2. If you're comparing an old quote to a new one, that gap matters.
Current Federal Minimums 3 ton or less— Southeast (2023)
| Equipment | Rating | Minimum |
|---|---|---|
| Split-system AC (single-stage) | SEER2 | 14.3 |
| Packaged / other AC units | SEER2 | 15.0 |
| Heat pump heating | HSPF2 | 7.5 |
| Gas furnace | AFUE | 80% |
Anything at 4 ton or larger, for our climate zone are 13.8.
Sources:
U.S. Department of Energy — Consumer Central Air Conditioners and Heat Pumps (standards overview, current): energy.gov/eere/buildings/consumer-central-air-conditioners-and-heat-pumps
Federal Register — Energy Conservation Standards for Residential Central Air Conditioners and Heat Pumps (Direct Final Rule, effective January 1, 2023): federalregister.gov/documents/2017/01/06/2016-29992
AHRI — 2023 Energy Efficiency Standards overview (SEER2/HSPF2): ahrinet.org/2023-energy-efficiency-standards
AHRI — Residential Heat Pumps (HSPF2 minimum standards): ahrinet.org/advocacy/residential-heat-pumps
U.S. DOE — Furnaces and Boilers (AFUE standards): energy.gov/energysaver/furnaces-and-boilers
What Ratings Don't Tell You
A rating is a ceiling, not a guarantee. It measures the equipment under controlled conditions — not your ductwork, your insulation, or how the system is sized for your home. A high-efficiency system in a leaky house will underperform a standard system in a tight one every time.
That's the subject of Part 2 — where we run the numbers on whether paying for a higher rating actually pencils out.