EER (Energy Efficiency Ratio): What It Means for HVAC Efficiency

What Is Energy Efficiency Ratio (EER)?

EER tells you how efficiently an air conditioner or heat pump is cooling at a specific operating condition, it’s a snapshot of efficiency at a fixed moment in time. It does not capture the full picture of efficiency for the unit. Think of it like the MPG rating for a car but only at highway speed. Just as a car's highway MPG doesn't tell you everything about fuel usage at everyday city driving speeds, EER doesn't capture how the equipment performs across all conditions throughout the year or season.  

For that, you'd look at other efficiency ratings like SEER/SEER2 or IEER/IEER2, depending on the equipment. 

What EER Measures: Cooling Output vs. Electrical Input

EER measures an air conditioner's efficiency by comparing its cooling output to the electrical power it consumes:

EER = Cooling Capacity (BTU/hr) ÷ Power Input (Watts)

The higher the EER, the more cooling you get for each watt of electricity drawn.

Why EER Is a "Single-Point" Efficiency Rating 

Unlike SEER or SEER2, which average efficiency across many operating conditions over an entire cooling season, EER is measured at one specific condition and at full load. This makes EER a good indicator of how equipment will behave on the hottest days of the year when demand is highest. 

What Types of Equipment Use EER 

EER is most commonly used with: 

• Packaged rooftop units (RTUs) 

• Split-system air conditioners 

• Unitary cooling equipment 

• Heat pumps (in cooling mode) 

• Larger commercial HVAC equipment (above 65,000 BTU/hr, where SEER2 does not apply) 

 

How EER Is Calculated 

The Formula 

EER = Cooling Capacity (BTU/hr) ÷ Power Input (Watts) 

Units Explained 

• BTU/hr (British Thermal Units per hour): the rate at which the unit removes heat from the space 

• Watts: the rate of electrical power consumed by the unit 

• A result of 11 means 11 BTU/hr of cooling for every 1 watt consumed. 

Step-by-Step Example 

Given: A rooftop unit with a cooling capacity of 120,000 BTU/hr and a rated power input of 11,000 watts at the standard test conditions. 

EER = 120,000 BTU/hr ÷ 11,000 W = 10.9 

This unit has an EER of 10.9 at the rating point. 

What You Need to Calculate EER 

• Cooling capacity in BTU/hr (sometimes listed in tons, 1 ton = 12,000 BTU/hr) 

• Power input in watts at the rated condition (not running amps alone) 

• Confirm both values are at the same rating condition (same outdoor temp, indoor conditions, and configuration) 

• Utilize AHRI’s testing conditions for the rating 

Common Calculation Mistakes 

• Mixing units: If power is listed in kilowatts (kW), convert to watts first: multiply by 1,000. Do not divide BTU/hr by kW directly. 

• Mismatched conditions: Make sure both capacity and power draw are from the same test point. Mixing a full-load capacity with a part-load power draw (or vice versa) produces a meaningless result.  

• Using nameplate amps: Running amperage alone is not sufficient. You need actual watt draw. 

 

EER Rating Test Conditions  

Standard Rating Conditions 

EER is measured under a standardized set of conditions established by AHRI (Air-Conditioning, Heating, and Refrigeration Institute) and ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers), and regulated by the DOE. The rating conditions are: 

• Outdoor air: 95°F dry-bulb 

• Indoor return air: 80°F dry-bulb / 67°F wet-bulb 

• Full-load operation 

These conditions represent a hot summer peak and are designed to make comparisons between manufacturers possible. 

Why Outdoor Temperature and Indoor Conditions Matter 

EER is temperature-sensitive. A unit rated with an EER of 11 under standard conditions will not achieve that same efficiency if your outdoor temperature is 105°F or your indoor return air temperature is different from the test point.  

How Airflow, Static Pressure, and Installation Affect Real-World Efficiency 

The rated EER assumes a specific airflow rate across the coil and a defined external static pressure. Things like undersized ductwork, dirty filters, or restrictive economizers can measurably reduce actual efficiency compared to the published rating. 

Why Comparing EER Across Different Configurations Can Be Misleading 

EER ratings apply to the specific unit configuration tested; for example, with or without an economizer or hot gas reheat. Comparing EER values from different equipment types, different configuration options, or different test conditions is an apples-to-oranges exercise. Always confirm that comparison units were rated under identical conditions before comparing them.  

EER vs. EER2 (The Updated Standard) 

What EER2 Is 

EER2 is the updated version of the EER metric, introduced as part of a larger effort (alongside SEER2) to better reflect real-world conditions. EER2 uses updated test procedures that include a higher external static pressure that more accurately represents how equipment performs once it’s in the field, not just in a lab. 

Why the Industry Moved to EER2 

Legacy EER test procedures used relatively low external static pressure values that didn’t reflect typical real-world conditions. Equipment rated under those conditions appeared more efficient than it would be in actual operation. EER2 corrects this by testing at more realistic conditions. 

Why EER2 Values May Look Different Than Legacy EER 

Because EER2 applies more realistic (and more demanding) test conditions, the published number is generally lower than legacy EER for the same piece of equipment. This is not a sign that equipment has gotten less efficient, it’s simply a more accurate representation of what the unit will deliver. 

Reading Spec Sheets That List EER vs. EER2 

Some products, particularly legacy or carry-over equipment still sold during the transition period may show both EER and EER2 values. When comparing equipment, always compare like for like: EER to EER, or EER2 to EER2. Never compare an EER value from one product against an EER2 value from another. 

Do You Need to “Convert” EER to EER2? 

There is no simple, universally accurate conversion factor between EER and EER2. The correct approach is to use manufacturer-published EER2 values whenever available, and to compare equipment under the same rating standard. 

What Is a Good EER (or EER2) Rating? 

"Good" is relative and depends on equipment type, climate, operating hours, and local utility rates. The industry accepts an EER of 12 or higher to be a high efficiency unit. 

Is a Higher EER Better? 

A higher EER means the system delivers more cooling per watt of electricity at the rating condition, which could translate to lower operating costs when the equipment is running at, or near, those rated conditions. 

The practical tradeoff is first cost vs. operating cost. Higher-EER equipment typically carries a higher purchase price.  

When is EER/EER2 not the most relevant metric for unit selection? If the unit runs only a few hours per day or spends most of its time at low part-load (common in more milder climates), the Seasonal Energy Efficiency Ratio (SEER/SEER2) or Integrated Energy Efficiency Ratio (IEER/IEER2) will provide a more accurate expectation of efficiency than EER/EER2.   

EER/EER2 vs. SEER/SEER2 vs IEER/IEER2 

Metric	What It Measures	Best Used For
EER / EER2	Efficiency at a single, specific peak condition (95°F OA)	Hot climates, peak-load applications, demand charge analysis
SEER / SEER2	Seasonal average efficiency across a range of conditions	Year-round energy cost comparisons, mild-to-moderate climates, residential and light commercial <65,000 BTU/hr
IEER / IEER2	Integrated Energy Efficiency Ratio; similar to SEER in that it measures efficiency across different loads	IEER measures efficiency across a range of operating loads, similar to SEER, but applies to commercial equipment rated above 65,000 BTU/hr

In hot climates where the system frequently operates at high capacity, EER/EER2 is often the more meaningful metric. In milder climates where the system runs at low loads for much of the season, SEER/SEER2 or IEER/IEER2 paints a more accurate picture of annual operating costs. 

Use both metrics together: EER/EER2 tells you how the unit will perform on the hottest days; SEER/SEER2 or IEER/IEER2 tells you the overall energy story across the season. Neither metric alone is sufficient for all decisions. 

Common comparison mistake: Do not compare EER/EER2 values from one product against SEER/SEER2 or IEER/IEER2 values from another. These metrics measure different things under different conditions. Always compare like with like.   

EER vs. COP 

What COP Is 

COP (Coefficient of Performance) is another efficiency ratio commonly used in in refrigeration and in HVAC heating applications (heat pumps in heating mode). COP is expressed as energy output divided by energy input, with both values in the same units (watts out per watt in). 

Converting Between EER and COP 

Because 1 watt = 3.412 BTU/hr, you can convert between EER and COP: 

COP = EER ÷ 3.412    |    EER = COP × 3.412 

Example: An EER of 10.2 equals a COP of approximately 2.99.  

When Spec Sheets Use COP Instead of EER 

You are most likely to encounter COP on spec sheets for heat pumps (particularly in heating mode), chillers tested under European or ISO standards, or equipment sold in international markets. 

EER in Commercial HVAC Selection 

Where EER Appears in Submittals and Product Literature 

EER/EER2 is typically found in the performance data tables of equipment submittals, product selection software output, AHRI certification data, and energy compliance documentation. It is often listed alongside SEER/SEER2 for smaller equipment and alongside IEER/IEER2 or IPLV  (Integrated Part-Load Value) for larger commercial units. 

Matching Apples-to-Apples 

When comparing EER/EER2 across equipment options, verify that all values are from the same configuration and rating. Utilize the AHRI certification database when accuracy is critical. 

Peak vs. Part-Load: Why You Should Also Consider Integrated Metrics 

Most commercial HVAC systems spend the majority of their operating hours at part load, not at the full-load peak captured by EER. For a more complete efficiency picture on larger commercial equipment, look at: 

• IEER (Integrated Energy Efficiency Ratio): a weighted average efficiency across multiple part-load conditions 

• IPLV (Integrated Part-Load Value): used for chillers and similar equipment 

EER captures the peak; IEER or IPLV captures the broader operating profile. 

How EER Relates to Demand Charges and Peak Pricing 

Demand charges (utility costs based on peak power) are directly influenced by what your equipment draws at its highest load point. A higher EER/EER2 unit will consume less energy at peak, reducing your demand charge exposure. In facilities with high demand charges, this can represent significant savings independent of total energy consumption. 

Checklist: What to Verify Before Choosing Equipment Based on EER 

• Are you comparing the same values, not mixing EER and EER2? 

• Is the configuration the same (with or without economizer, same refrigerant)? 

• Have you confirmed values against AHRI-certified data? 

• Have you also reviewed IEER2 or SEER2 for part-load and seasonal context? 

• Have you accounted for local utility rates? 

How to Improve Effective EER in the Field 

The nameplate EER/EER2 is the best-case scenario under ideal conditions. Here’s how to maximize it during design, installation, commissioning, and operation. 

Design Factors 

• Right-sizing: Oversized equipment short-cycles and operates inefficiently. An accurate load calculation ensures the unit can achieve its rated EER/EER2 at design conditions. 

• Ventilation strategy: Minimize unnecessary outdoor air load during peak conditions  

• Controls: Specify controls that allow the unit to run at or near design conditions rather than fighting against poorly calibrated setpoints. 

Installation Factors 

• Airflow setup: Ensure supply and return air paths are sized and balanced to match the unit’s rated airflow. Restriction reduces cooling capacity and raises power draw simultaneously. 

• Duct and static pressure: Excessive external static pressure forces the fan to work harder. 

• Economizer setup: Where applicable, ensure the economizer is properly configured. A stuck-open damper on a hot day dramatically increases load and reduces efficiency. 

Commissioning Factors 

• Sensor calibration: Temperature and pressure sensors that are out of calibration cause the controls to make incorrect decisions, running the unit harder than necessary. 

• Setpoints: Overly aggressive cooling setpoints force the unit to operate at peak capacity more often. Verify setpoints reflect actual occupant needs. 

• Sequences of operation: Confirm that control sequences enable the unit to stage properly and avoid unnecessary full-capacity operation during low-load periods. 

Maintenance Factors 

• Coils: Dirty condenser or evaporator coils reduce heat transfer efficiency and force the compressor to work harder, directly reducing effective EER/EER2. 

• Filters: Clogged filters increase static pressure and reduce airflow, compounding efficiency loss. 

• Refrigerant circuit: Low refrigerant charge can reduce capacity and efficiency. Verify charge per manufacturer specifications. 

• Belts and bearings (where applicable): Worn or misaligned drive components increase power consumption. 

Operational Best Practices 

• Scheduling: Avoid running cooling equipment at full capacity during peak utility periods where possible. Pre-cooling during off-peak hours can reduce demand charges. 

• Setback: Raising the cooling setpoint during unoccupied hours reduces full-load run time and peak demand exposure. 

• Monitoring: Use energy metering or building automation trend data to track actual system power draw and catch efficiency degradation early. 

 

Key Takeaways (Summary) 

Topic	Summary
What EER measures	EER (Energy Efficiency Ratio) is a rating that measures how efficient an air conditioner or heat pump unit is at specific conditions, by dividing its cooling capacity by its electrical input.
Higher EER = ?	A higher EER means the unit is more efficient at peak (full-load) cooling conditions, resulting in lower energy consumption and reduced operating costs during those peak periods.
When EER matters most	EER is most relevant in hot climates or applications where the system runs at, or near, full capacity for the majority of the time. It is the better indicator of peak-condition energy performance.
EER vs. EER2	The HVAC industry has moved to EER2, which uses updated test procedures to better represent real-world performance.
How to use EER alongside SEER2	SEER2 applies to equipment under 65,000 BTU/hr and measures seasonal average efficiency. Use SEER2 for year-round cost comparisons; use EER/EER2 when peak-load or hot-weather efficiency is the primary concern.

Frequently Asked Questions 

What does EER mean in HVAC? 

EER (Energy Efficiency Ratio) measures how efficiently an air conditioner or heat pump delivers cooling at a specific set of test conditions. It measured the cooling output divided by electrical power input. A higher EER means more cooling for the same electricity consumed. 

What is the EER formula? 

EER = Cooling Capacity (BTU/hr) ÷ Power Input (Watts) 

How do I calculate EER for an HVAC unit? 

You need two values from the equipment at the rating condition: (1) cooling capacity in BTU/hr, and (2) power draw in watts. Divide BTU/hr by watts. If power is listed in kilowatts (kW), multiply by 1,000 to convert to watts first. 

What is a good EER rating for an air conditioner? 

"Good" depends on equipment type and application, but higher is always better. For modern commercial equipment, values above 12 are considered high efficiency.  

Is a higher or lower EER better? 

Higher is better. A higher EER means the unit delivers more cooling per watt of electricity at the rating point. All else being equal, the unit with the higher EER will cost less to operate under the rated conditions. 

What’s the difference between EER and SEER? 

EER measures efficiency at a single, specific operating condition (95°F outdoor temperature). SEER measures seasonal average efficiency across a range of conditions over the entire cooling season. EER tells you about hot-weather peak performance; SEER gives you the full-season energy picture. 

What’s the difference between EER and COP? 

Both describe efficiency, but in different units. EER is expressed as BTU/hr per watt; COP is watts of output per watt of input. They describe the same performance but are used in different applications and regions. You can convert between them: COP = EER ÷ 3.412. 

Can I convert EER to EER2? 

There is no universally accurate conversion factor because EER2 uses a different test procedure (higher external static pressure) and the impact varies by equipment design. Use manufacturer-published EER2 values whenever available and always compare units under the same rating standard. 

What is EER used for and when should I pay attention to it? 

EER is most useful when you need to understand hot-weather or peak-load cooling efficiency. 

Why does my real-world efficiency differ from the rated EER? 

Rated EER is measured under controlled laboratory conditions. Real-world performance varies due to: 

• Outdoor and indoor conditions that differ from the standard test point 

• Airflow and static pressure differences from design assumptions 

• Controls and part-load operation (the unit rarely runs at exactly full load) 

• Installation quality, including duct design and economizer configuration 

• Maintenance status, things like dirty coils, clogged filters, or low refrigerant charge all reduce efficiency