EER, SEER, SEER2 — what each rating actually measures
EER — Energy Efficiency Ratio
EER measures how efficiently an air conditioner operates at a single fixed condition: 95°F
outdoor, 80°F indoor dry-bulb, 50% relative humidity. It is calculated as:
EER = BTU/hr of cooling ÷ watts of electricity consumed
An EER of 10 means the unit delivers 10 BTU of cooling per watt of electricity at peak conditions.
EER is most useful for comparing units that will primarily operate at hot peak conditions, such as
window ACs in hot climates or packaged rooftop units. The higher the EER, the more efficient the unit
at its rated peak.
SEER — Seasonal Energy Efficiency Ratio (pre-2023)
SEER improves on EER by measuring efficiency across a full cooling season — a mix of hot days,
mild days, and part-load operation. It is defined as total BTU of cooling delivered divided by total
watt-hours consumed across the season. The test conditions assume outdoor temperatures from 65°F
to 104°F and static pressure of 0.1 in. water gauge on the air handler side.
SEER was the DOE standard from 1992 through 2022.
SEER2 — Current DOE Standard (2023 & beyond)
SEER2 uses the same seasonal averaging concept as SEER but updates the test conditions to better
reflect real installed performance. The key change is raising the static pressure from 0.1 in. to
0.5 in. water gauge, which accounts for real ductwork resistance. This makes SEER2
numbers approximately 4–5% lower than SEER for the same equipment. A unit
rated SEER 16 under the old standard is approximately SEER2 15.2 under the new standard.
All new central AC and heat pump equipment manufactured for sale in the US since January 1, 2023
is rated in SEER2.
COP — Coefficient of Performance
COP is a dimensionless ratio used internationally and in engineering contexts. For cooling,
COP = BTU/hr of cooling ÷ 3.412 ÷ watts = SEER2 ÷ 3.412. A SEER2 16 unit has a
seasonal COP of about 4.69 — meaning it delivers 4.69 units of cooling energy for every unit
of electrical energy consumed across the season.
kW/ton — Commercial Efficiency Metric
kW/ton measures how many kilowatts of electricity a unit consumes per ton of cooling capacity.
Lower is more efficient. It is commonly used for commercial chillers and large HVAC equipment.
kW/ton = 12 ÷ EER (since 1 ton = 12,000 BTU/hr and EER = BTU/hr per watt).
A residential unit with EER 12 draws approximately 1.0 kW/ton at peak conditions.
Efficiency conversion reference table
| SEER2 |
SEER (approx.) |
EER (approx.) |
COP (seasonal) |
kW/ton (peak) |
DOE Grade |
| 13.4 | 14.1 | 12.6 | 3.93 | 0.95 | Minimum (North) |
| 14.3 | 15.1 | 13.5 | 4.19 | 0.89 | Minimum (South) |
| 15 | 15.8 | 14.1 | 4.40 | 0.85 | Good |
| 16 | 16.8 | 15.0 | 4.69 | 0.80 | Good |
| 18 | 18.9 | 16.9 | 5.28 | 0.71 | High-efficiency |
| 20 | 21.1 | 18.8 | 5.86 | 0.64 | High-efficiency |
| 22 | 23.2 | 20.7 | 6.45 | 0.58 | Premium |
| 26 | 27.4 | 24.5 | 7.62 | 0.49 | Top-tier premium |
SEER ≈ SEER2 ÷ 0.95. EER ≈ SEER2 ÷ (1.12 × 0.95). COP = SEER2 ÷ 3.412.
kW/ton at peak = 12 ÷ EER. Values are approximations; actual ratings depend on equipment design.
2023 DOE minimum efficiency standards
The U.S. Department of Energy's updated minimum efficiency standards took effect on
January 1, 2023 for all new residential central air conditioners and air-source
heat pumps manufactured for sale. Equipment manufactured before that date can still be installed
under the old SEER minimums.
| Equipment Type |
Region |
Minimum SEER2 |
Former SEER Minimum |
| Central split-system AC (≤ 45,000 BTU/hr) |
North (Zones 4–8) |
13.4 SEER2 |
13 SEER |
| Central split-system AC (≤ 45,000 BTU/hr) |
South & Southwest (Zones 1–3) |
14.3 SEER2 |
14 SEER |
| Central split-system heat pump |
All regions |
14.3 SEER2 |
14 SEER |
| Single-package central AC |
All regions |
13.4 SEER2 |
14 SEER |
| Window AC (< 8,000 BTU/hr) |
All regions |
EER 10.9 (not SEER2) |
EER 10.7 |
| Portable AC (single-duct) |
All regions |
CEER 8.0 (not SEER2) |
CEER 8.0 |
ENERGY STAR certification requires higher efficiency than the federal minimum:
ENERGY STAR Central AC requires SEER2 ≥ 15.2 (North) or SEER2 ≥ 15.2 (South).
ENERGY STAR Heat Pump requires SEER2 ≥ 15.2 and HSPF2 ≥ 7.5.
What SEER2 rating should you buy?
Higher SEER2 equipment costs more upfront but uses less electricity. The right efficiency tier
depends on how many hours per year you cool, your electricity rate, and the premium you pay for
a more efficient unit.
| Climate Zone |
Cooling Hrs/yr |
Sweet-Spot SEER2 |
Why |
| Zone 1–2 (Miami, Phoenix, Houston) |
1,800–2,200 |
18–22 |
Long cooling seasons make every efficiency point pay back quickly. High-efficiency units often pay back their premium in 4–6 years. |
| Zone 3 (Atlanta, Dallas, LA) |
1,200–1,600 |
16–20 |
Good ROI on efficiency. SEER2 18–20 typically pays back in 5–8 years at average electricity rates. |
| Zone 4 (NYC, DC, Seattle) |
800–1,100 |
15–18 |
Moderate payback. Going above SEER2 18 often has a payback over 10 years unless electricity rates are above 20¢/kWh. |
| Zone 5 (Chicago, Boston, Denver) |
500–800 |
14–16 |
Fewer cooling hours reduce the annual savings from higher efficiency. The minimum-compliant 13.4 SEER2 is often the best financial choice. |
| Zone 6–7 (Minneapolis, Duluth) |
300–500 |
13.4–15 |
Very short cooling seasons mean almost no payback on premium efficiency. Spend the money on heating efficiency (HSPF2) instead. |
Payback estimates assume a $150–$300 premium per SEER2 point above minimum and electricity at
16¢/kWh for a 3-ton system. Higher electricity rates or larger systems improve the payback
calculation. Use the “Old vs new savings” tab above with your own numbers.
Frequently asked questions
What is the difference between EER, SEER, and SEER2?
EER measures efficiency at one fixed peak condition (95°F outdoor). SEER
measures seasonal average efficiency at 0.1 in. static pressure (old standard). SEER2
measures seasonal average efficiency at 0.5 in. static pressure, better matching real duct installations
(current 2023 DOE standard). SEER2 values are about 4–5% lower than the same equipment’s
SEER rating.
How do I convert my old SEER rating to SEER2?
Use: SEER2 = SEER × 0.95. A unit rated SEER 16 is approximately SEER2 15.2.
This conversion applies to central split-system AC and heat pumps. Mini splits, window ACs, and
packaged units use different test procedures and their conversion factors may vary.
Does SEER2 replace EER entirely?
No. EER is still used for window ACs, PTACs, and some commercial equipment where peak-load efficiency
matters more than seasonal average efficiency. CEER (Combined Energy Efficiency Ratio) is used for
portable ACs. SEER2 replaced SEER only for central split-system AC and heat pump equipment.
Is a 16 SEER2 mini split better than a 16 SEER2 central AC?
They’re tested to the same standard, but mini splits typically achieve much higher real-world
efficiency because they have no duct losses (ducts typically waste 15–25% of conditioned air).
A 16 SEER2 mini split often outperforms a 20 SEER2 central AC system in a home with leaky ductwork.
What is the most efficient AC you can buy in 2026?
Top residential mini splits (Mitsubishi Hyper Heat, Daikin, LG Art Cool) reach SEER2 ratings of
22–28 for single-zone units. Whole-home variable-speed central AC systems top out around
SEER2 20–24. Geothermal heat pumps have effective EER of 15–30 but are tested under
a separate standard (EER at 59°F ground temperature).
How do you convert EER to SEER?
The commonly used approximation is SEER ≈ EER × 1.12 for central AC systems.
This is an estimate — actual SEER depends on part-load performance. To convert to SEER2, use
SEER2 ≈ SEER × 0.95. So EER 10 converts to approximately
SEER 11.2, or SEER2 10.6. Use the conversion calculator above for
instant results across all five metrics.
What is the minimum SEER2 required by DOE in 2023?
The 2023 DOE minimum SEER2 requirements are 13.4 SEER2 for central split-system
AC in the North (IECC Zones 4–8) and 14.3 SEER2 for the South and Southwest
(Zones 1–3). Heat pumps require 14.3 SEER2 in all regions. Window and portable ACs use
different standards (EER and CEER respectively) — see the compliance table above.
How much money does a higher SEER2 save per year?
Upgrading from SEER2 13 to SEER2 20 saves roughly 35% on cooling electricity costs. For a 3-ton
central AC in a Zone 3 climate running 1,400 hours/year at 16¢/kWh, that's approximately
$130–$180 per year. Savings are proportional to system capacity, annual
cooling hours, and electricity rate. Use the Old vs new savings tab
with your exact numbers.
How do you convert SEER2 to COP or kW per ton?
COP = SEER2 ÷ 3.412 — the ratio of BTU output to watt input across the
cooling season. kW/ton = 12 ÷ EER — since 1 ton = 12,000 BTU/hr and
EER = BTU/hr per watt. A SEER2 16 unit has a seasonal COP of approximately 4.69 and draws
roughly 0.92–1.00 kW per ton at peak conditions. See the
efficiency conversion table above for a full reference.
Does a higher SEER2 also mean better heating efficiency?
Not directly. For heat pumps, heating efficiency is measured separately as HSPF2 (Heating Seasonal
Performance Factor 2). A unit with a high SEER2 does not automatically have a high HSPF2, though
variable-speed compressor designs that produce high SEER2 ratings tend to also produce good HSPF2
ratings. If you’re buying a heat pump for a cold climate, check both SEER2 and HSPF2.