Quick answer
EER2 is the energy efficiency ratio of an air conditioner or heat pump at one hot, steady condition: the cooling it delivers in BTU per hour divided by the electric power it draws in watts, with 95°F outside, tested under the federal Appendix M1 procedure in force since 2023.
Where SEER2 averages a whole season, EER2 is a snapshot of the hardest hour. It replaced the older EER, which used lower duct resistance.
Quick facts
The key facts about EER2, with sources:
- Outdoor test temperature
- 95°F dry bulb 1
- Test procedure
- 10 CFR 430 Appendix M1, from 1 January 2023 2
- Where it is a legal minimum
- Southwest only: Arizona, California, Nevada, New Mexico 1
- Southwest floor, split AC under 45,000 BTU/h
- 11.7 EER2 if SEER2 is below 15.2; 9.8 EER2 if SEER2 is 15.2 or more 1
- Replaced
- EER (2015–2022 Southwest floor 12.2 EER for small split AC) 1
Key takeaways
- EER2 tells you how efficient a system is on a very hot afternoon, running flat out.
- It is tested at 95°F outside. SEER2, by contrast, averages many cooler conditions 1.
- Only the four Southwest states make EER2 a legal minimum for new central air conditioners 1.
- Two units with the same SEER2 can have quite different EER2. In a hot desert climate the higher EER2 usually wins.
- The old rating, EER, used an easier duct test. Do not compare an old EER with a new EER2.
What EER2 measures
EER2 is the simplest of the cooling ratings. The lab holds the outdoor side at 95°F and runs the system at full capacity.
It measures the cooling delivered, in BTU per hour, and the electric power used, in watts. Divide one by the other and you have EER2.
A 12 EER2 unit moves 12 BTU per hour of heat for each watt.
The federal rule defines the figure "at a standard rating of 95°F dry bulb outdoor temperature" 1. Under the Appendix M1 test, the indoor fan also works against realistic duct resistance: 0.50 inches of water column for a conventional ducted system 2.
The name is old. Engineers used energy efficiency ratio, or EER, for decades. The "2" was added in 2023 when DOE switched every central air conditioner and heat pump to the M1 test.
EER vs EER2: what changed in 2023
The math did not change. The test conditions did. Under the old Appendix M test, a ducted system pushed air against only 0.10 to 0.20 inches of resistance, depending on its size.
Appendix M1 raised that to 0.50 inches for a conventional ducted system 2. A harder-working fan draws more watts, so the same unit earns a lower number as EER2 than it did as EER.
The Southwest floor moved with it. From 2015 to 2022, a split air conditioner under 45,000 BTU/h in Arizona, California, Nevada or New Mexico needed 12.2 EER. Since 1 January 2023 it needs 11.7 EER2 1. The figure looks lower, but it is measured under a stricter test.
There is one twist. The 2023 rule gives systems rated 15.2 SEER2 or higher a lower EER2 floor, 9.8 1. Many high-SEER2 units use variable-speed compressors that shine at part load but lose some ground at full blast. The rule lets them in, as long as their seasonal rating is high.
One EER2 test point, step by step
- Outdoor room held at 95°F → indoor room held at standard return-air conditions
- System runs at full cooling capacity → no cycling, no part load
- Indoor fan pushes against M1 duct resistance → fan watts counted
- Cooling output (BTU/h) ÷ total watts → EER2, rounded to 0.025
Southwest EER2 minimums for new central air conditioners
| Product | Certified SEER2 below 15.2 | Certified SEER2 15.2 or higher |
|---|---|---|
| Split AC, under 45,000 BTU/h | 11.7 EER2 | 9.8 EER2 |
| Split AC, 45,000 BTU/h and up | 11.2 EER2 | 9.8 EER2 |
| Packaged (single-package) AC | 10.6 EER2 | 10.6 EER2 |
Which rating matters on which kind of day
| Rating | The day it describes | What it captures | Blind spot |
|---|---|---|---|
| EER2 (this page) | A 95°F afternoon, system at full speed | Peak cooling efficiency and the load on the grid | Says nothing about mild days, part load or heating |
| SEER2 | A whole summer of warm and mild days | Seasonal average cooling efficiency | Can hide weak performance in extreme heat |
| HSPF2 | A whole winter in a moderate climate | Seasonal heat pump heating efficiency | Weak guide for long stretches below 17°F |
| AFUE | A year of furnace or boiler heating | Share of fuel turned into heat at the unit | No cooling; ignores duct loss and blower power |
Example: two units, same SEER2, different EER2
Two 3-ton systems (36,000 BTU/h) both rate 16 SEER2. Unit A lists 13.0 EER2; Unit B lists 10.0 EER2. These are example ratings, not specific products. Check real pairs in the AHRI Directory 5. Power draw at 95°F = capacity ÷ EER2.
| At 95°F, full load | Unit A (13.0 EER2) | Unit B (10.0 EER2) |
|---|---|---|
| Power draw | 36,000 ÷ 13.0 = 2,769 W | 36,000 ÷ 10.0 = 3,600 W |
| Per 100 peak hours | 277 kWh | 360 kWh |
| Energy cost per 100 peak hours at 18.31¢/kWh (US average, July 2026) | about $50.70 | about $65.92 |
On paper the two units tie for the season. On the hottest afternoons Unit B draws about 830 watts more.
In Phoenix or Las Vegas, where many summer hours sit near or above 95°F, that gap adds up and can strain a tight electrical panel. In Seattle it hardly matters. Price per kWh from EIA 4.
Where EER2 appears
- On the AHRI certificate, next to SEER2 and capacity, for each matched pair 5.
- On spec sheets, often in a performance table by outdoor temperature.
- On Southwest rebate and code paperwork, since the federal rule uses it there.
- On utility peak-demand programs, which care about watts on the hottest day.
- Rarely on the yellow EnergyGuide label, which leads with SEER2. Ask for it.
Sources: [5]
Why EER2 is worth checking
Strengths
- Shows how a unit copes with the heat that actually drives your bills in hot climates.
- Tells you the peak watts, which matters for panel size, generators and solar sizing.
- Simple: one test point, one ratio, easy to compare.
- Helps utilities and the grid, since peak demand is what strains power lines.
Limits
- Only one temperature. Most cooling hours in most states are cooler than 95°F.
- Undersells variable-speed systems, which save most at part load.
- Not a legal minimum outside the Southwest, so many quotes leave it out.
- Like SEER2, valid only for the listed outdoor and indoor pairing.
What EER2 cannot tell you
EER2 stops at 95°F. A desert roof can push the condenser into air well above that, and a unit’s efficiency keeps falling as it gets hotter. The spec sheet’s extended performance table is the place to see 105°F or 115°F behavior.
It also assumes a clean, correct install. NIST found duct leakage, refrigerant undercharge and low indoor airflow among the faults that most raise a heat pump’s yearly energy use 7. A label cannot show those.
And it says nothing about humidity. Full-load efficiency and moisture removal are different jobs. In humid Southeast summers, a unit that slows down and runs longer may feel better even with a lower EER2.
Sources: [7]
Cost drivers and what EER2 does to them
High EER2 usually comes from a large outdoor coil and an efficient fixed-speed or two-stage compressor. High SEER2 with low EER2 often points to a variable-speed design. Both add hardware, and hardware adds price.
EER2 also shapes hidden costs. Fewer peak watts can mean a smaller breaker, less risk of a panel upgrade and lower demand charges on time-of-use rates. See how panel capacity affects an HVAC job.
HyreHVAC does not print equipment prices until enough dated quotes support them. The HVAC cost calculator shows what moves the total.
How to use EER2 when comparing quotes
- Get the full model numbers for the outdoor unit and indoor coil or air handler.
- Ask for the AHRI reference number and confirm the EER2 and SEER2 listed there.
- If you live in AZ, CA, NV or NM, check that the pair meets the regional EER2 floor for its SEER2 band.
- If you have many hours above 95°F, ask for the extended performance table at 105°F and 115°F.
- Confirm the contractor did a load calculation, then sized ducts to match. EER2 assumes the airflow is right.
Install, electrical work and refrigerant charging are for licensed contractors. Refrigerant handling needs EPA Section 608 certification.
Keeping peak efficiency up
- A dirty outdoor coil hurts most on the hottest days. Hose off loose debris from outside, power off, or book a coil cleaning 8.
- Shade helps the air around the unit, but keep plants at least 2 feet away so air can flow.
- Replace the filter when dirty. A clogged filter cuts airflow and full-load efficiency.
- Have the charge and airflow checked each spring, before the first heat wave 8.
Sources: [8]
Signs the system is struggling in the heat
- The house cannot hold the set point on a 100°F day and the unit never shuts off.
- The breaker trips on the hottest afternoons.
- The outdoor fan runs but the copper lines feel warm, or the unit hums without starting.
- A sharp jump in summer bills after a repair.
- Call a licensed HVAC technician for any of these. Do not open electrical panels or touch refrigerant lines.
The rules behind EER2
DOE sets the Southwest EER2 floors in 10 CFR 430.32(c)(6)(i). They apply to split and packaged air conditioners installed on or after 1 January 2023 in Arizona, California, Nevada and New Mexico. A model rated below the level "cannot be installed in that region" 1.
EER2 is measured under Appendix M1, section 2, and rounded to the nearest 0.025 2. Manufacturers rate to AHRI 210/240 6.
ENERGY STAR asks split heat pumps for at least 11.0 EER2 and packaged heat pumps for 10.0, beside 15.2 SEER2 3. Full state lists are in our regional standards research.
EER and EER2 misconceptions
- Myth EER2 and SEER2 are the same number in different units.
- Reality No. EER2 is one hot test point; SEER2 averages a season. Expect them to differ, and read both.
- Myth A higher SEER2 always means a higher EER2.
- Reality Not always. Variable-speed units can have high SEER2 and a modest EER2.
- Myth EER2 only matters in Arizona.
- Reality It is only a legal minimum there, but anyone with long, hot summers or a tight panel benefits from checking it.
- Myth My old 12 EER unit beats a new 11.7 EER2 unit.
- Reality The tests differ. The newer one may draw the same power or less.
Why the desert Southwest uses EER2
DOE added the EER floor for Arizona, California, Nevada and New Mexico because hot, dry afternoons there drive peak demand on the grid.
Southeast states such as Florida, Georgia and Texas have a SEER2 floor but no EER2 floor 1.
If your area logs many cooling degree days, EER2 deserves a look even where it is not required.
When EER2 should change your choice
Use EER2 as a tie-breaker between units with similar seasonal ratings. A practical rule: if your summer has many hours near 95°F or above, or your panel is close to full, favor the higher EER2. If your summer is mild and humid, favor variable-speed comfort and SEER2 instead.
Next step: plug your hours into the SEER2 savings calculator, and check whether a new system fits your panel with a licensed electrician. Our heat pump shortlist lists rated pairs.
Questions about EER2
What is a good EER2 rating?
A good EER2 depends on your climate. In the Southwest, the legal floor for a small split air conditioner is 11.7 EER2, or 9.8 if its SEER2 is 15.2 or higher.
ENERGY STAR split heat pumps need 11.0 EER2. In hot, dry climates, 12 or more is a strong figure. In mild climates, EER2 matters less than SEER2.
What is the difference between EER2 and SEER2?
EER2 is measured at a single 95°F full-load test point, while SEER2 averages performance across a whole cooling season. EER2 shows how a unit copes with peak heat. SEER2 shows typical seasonal use. A system can score high on one and modest on the other, so read both when summers are hot.
Is EER the same as EER2?
They use the same formula but different tests. EER2 is measured under the Appendix M1 procedure that took effect on 1 January 2023, which makes the fan push against more duct resistance. That lowers the result. Old EER and new EER2 figures should not be compared directly.
Which states require a minimum EER2?
Arizona, California, Nevada and New Mexico. In those four states, new split and packaged central air conditioners installed since 1 January 2023 must meet an EER2 floor as well as a SEER2 floor. Other regions have SEER2 rules only. The rule is in 10 CFR 430.32(c)(6).
Why is the EER2 lower on my high-SEER2 unit?
High-SEER2 units often use variable-speed compressors. These run slowly and very efficiently most of the time, which boosts SEER2.
At full speed on a 95°F day they lose some of that edge, so EER2 can be lower.
DOE allows a 9.8 EER2 floor in the Southwest for units rated 15.2 SEER2 and up for that reason.
How do I calculate EER2?
Divide the cooling capacity in BTU per hour by the power draw in watts, both at the 95°F rating point. A 36,000 BTU/h unit drawing 3,000 watts is 12 EER2. You cannot measure the rated value at home, because it needs lab conditions. Use the AHRI listing for the official number.
Does EER2 matter for a heat pump?
Yes, for its cooling side. A heat pump has SEER2 and EER2 for cooling and HSPF2 for heating. The Southwest regional EER2 rule covers air conditioners only, but ENERGY STAR asks heat pumps for at least 11.0 EER2 for split systems. If you cool more than you heat, EER2 is worth checking.
Where can I find a unit’s EER2?
The AHRI Directory lists EER2 for each certified outdoor and indoor pairing. Most spec sheets show it too. The yellow EnergyGuide label usually leads with SEER2, so ask your contractor for the AHRI reference number if EER2 is not shown on the quote.
Does a higher EER2 lower my peak electricity bill?
It can. EER2 sets how many watts a unit draws at full load in hot weather. On a time-of-use or demand rate, fewer peak watts cost less. In our example, a 13.0 EER2 unit drew about 830 watts less than a 10.0 EER2 unit of the same size at 95°F.
Sources
- eCFR, 10 CFR 430.32 Energy and water conservation standards and their compliance dates (current text), retrieved .
- GovInfo, 10 CFR part 430 (2024 annual edition), subpart B appendices M and M1, retrieved .
- ENERGY STAR, Air-Source Heat Pumps key product criteria, retrieved .
- U.S. EIA, Electric Power Monthly, Table 5.6.A Average price of electricity by state, July 2026 and 2025, retrieved .
- AHRI Directory of Certified Product Performance, retrieved .
- AHRI Standard 210/240, Performance Rating of Unitary Air-conditioning and Air-source Heat Pump Equipment, retrieved .
- NIST Technical Note 1848, Sensitivity Analysis of Installation Faults on Heat Pump Performance (2014), retrieved .
- ENERGY STAR, Maintenance Checklist for heating and cooling, retrieved .
Expert review
Written by the HyreHVAC Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Regional EER2 floors and the 2015 EER floors read from the current eCFR text of 10 CFR 430.32; test conditions from Appendices M and M1; ENERGY STAR criteria from its key product criteria page. The two-unit example uses labelled hypothetical ratings.
Suggest a correction. We fix errors and say what changed.