We use cookies and similar technologies — including Google Analytics and Google AdSense — to measure traffic and serve relevant ads.
By clicking Accept you consent to our use of these technologies.
See our Privacy Policy for details.
Shopping for a new AC, heat pump, or furnace? The efficiency rating is the biggest driver of long-term operating cost — but the acronyms are confusing. This guide explains what each number means, the 2024 federal minimums, and how to pick the right tier for your climate.
SEER2
Cooling Efficiency
Central AC & Heat Pumps Min: 13.4 | Good: 16+ | Best: 20+ Higher = cheaper to cool
HSPF2
Heat Pump Heating
Heat Pumps only Min: 7.5 | Good: 9+ | Best: 11+ Higher = cheaper to heat
AFUE
Furnace Efficiency
Gas & Oil Furnaces Min: 80% | Good: 90%+ | Best: 96–98% Higher = less fuel wasted
SEER2 — Seasonal Energy Efficiency Ratio
SEER2 measures how much cooling an AC or heat pump delivers per watt-hour of electricity over an entire cooling season. Higher SEER2 = less electricity used per hour of cooling.
The "2" suffix arrived in January 2023 when the DOE updated the test procedure to better reflect real-world duct conditions. SEER2 ratings run about 4–5% lower than old SEER on the same equipment. A "16 SEER" unit now appears as roughly "15.2 SEER2" — they're the same machine.
Rule of thumb: Every 2-point increase in SEER2 saves roughly 10–12% on your cooling electricity bill. Going from 14 to 18 SEER2 on a typical 3-ton system can save $80–$150/year depending on rates and climate.
What SEER2 to buy?
Mild climate (Zones 1–3): 14–15 SEER2 is fine. Payback on premium units is too long.
Moderate climate (Zone 4): 16–17 SEER2 offers a 5–8 year payback for most homes.
Hot/humid climate (Zones 5–7): 18–20 SEER2 makes financial sense — high usage means faster payback.
HSPF2 — Heating Seasonal Performance Factor
HSPF2 applies only to heat pumps and measures heating output per watt-hour of electricity over a full heating season. It is the heat pump equivalent of AFUE. The federal minimum is 7.5 HSPF2 for split systems.
Target 9.0+ HSPF2 for a good efficiency-to-cost balance. Cold-climate heat pumps designed for sub-zero temperatures sometimes rate lower in HSPF2 but still outperform electric resistance heating (baseline: ~3.4 HSPF2).
Key fact: Even a minimum-efficiency heat pump (7.5 HSPF2) delivers 2–3x more heat per watt than a standard electric resistance heater, and often beats a high-efficiency gas furnace when electricity is under $0.18/kWh.
AFUE — Annual Fuel Utilization Efficiency
AFUE measures what percentage of a furnace's fuel becomes useful heat. An 80% AFUE furnace wastes 20 cents of every gas dollar up the flue. A 96% AFUE condensing furnace wastes only 4 cents.
Is upgrading from 80% to 96% AFUE worth it?
Cold climates: Absolutely. In Minneapolis with 1,200+ furnace hours/year, payback can be 4–6 years.
Mild climates: Less clear. In Phoenix at 400 furnace hours/year, payback may stretch to 10–15 years.
Gas price matters: At $2.50+/therm, high-efficiency furnaces earn back the premium in 3–5 years.
Comparison Table
Rating
Applies To
What It Measures
2024 Min
Efficient
High-Efficiency
SEER2
AC, Heat Pump
Cooling output / electricity (seasonal)
13.4
16–17
20+
HSPF2
Heat Pump
Heating output / electricity (seasonal)
7.5
9–10
11+
AFUE
Gas Furnace
Heat delivered / fuel burned
80%
90–94%
96–98%
EER2
Window / Mini-Split
Cooling output / electricity (steady-state)
9.8
12–14
16+
Frequently Asked Questions
What is a good SEER2 rating for an air conditioner?
The federal minimum is 13.4 SEER2. A rating of 16–18 SEER2 is efficient; 20+ is high-efficiency. In hot climates like the South, 18+ SEER2 can offer faster payback due to high cooling hours.
What is the difference between SEER and SEER2?
SEER2 uses the updated M1 test procedure (January 2023) that applies higher external static pressure — a tougher, more realistic test. SEER2 runs roughly 4–5% lower than equivalent SEER on the same unit. Always compare units using the same rating standard.
What AFUE rating should I look for in a furnace?
The federal minimum is 80% AFUE (90%+ required in northern states). High-efficiency condensing furnaces reach 95–98% AFUE. Upgrading from 80% to 96% AFUE can cut heating fuel costs by ~17% annually, with a typical payback of 5–8 years.
What does HSPF2 mean for a heat pump?
HSPF2 measures heat pump heating efficiency over a full season — the higher the number, the less electricity used per BTU of heat. The minimum is 7.5; efficient models reach 10–12 HSPF2. Cold-climate heat pumps for sub-zero temps sometimes have lower HSPF2 ratings but are still your best option for extreme cold.
Ready to size your system?
Use our free calculators to find the right tonnage, CFM, and duct size for your home.