EER2 (Energy Efficiency Ratio 2) is a seasonal energy efficiency metric that measures the cooling performance of air conditioning equipment by calculating the ratio of cooling output in Btu/h to electrical power input in watts under updated testing procedures. It applies primarily to single-package air conditioners and heat pumps with cooling capacities below 65,000 Btu/h that use single-phase power. EER2 replaced the legacy EER rating to provide a more accurate representation of real-world energy performance across varying load conditions rather than relying on a single full-load test point.
Technical Details and Testing Conditions
EER2 is calculated using testing procedures aligned with the Integrated Energy Efficiency Ratio (IEER) methodology, which evaluates equipment performance at multiple part-load operating points. The standard rating conditions include a 95°F outdoor dry-bulb temperature and indoor conditions of 80°F dry bulb and 67°F wet bulb. By incorporating part-load data into the efficiency calculation, EER2 captures how units perform during typical cycling patterns, not just at peak demand. A higher EER2 value indicates greater energy efficiency. EER2 values are generally lower numerically than legacy EER ratings for the same piece of equipment due to the differences in test methodology, so the two metrics should not be compared directly.
Applications and Equipment Scope
EER2 is used to rate the following categories of commercial and residential equipment:
- Single-package air conditioners under 65,000 Btu/h
- Single-package heat pumps under 65,000 Btu/h (cooling mode)
- Central air conditioning systems where EER-based compliance was previously required
The metric is particularly relevant for building owners, engineers, and contractors evaluating packaged rooftop units, light commercial systems, and certain residential applications where equipment selection must meet both performance needs and regulatory thresholds.
Related Standards and Regulatory Context
The U.S. Department of Energy (DOE) adopted EER2 as part of its updated minimum efficiency standards that took effect on January 1, 2023. These regulations align with AHRI 210/240 testing standards and require manufacturers to publish EER2 ratings on all applicable equipment. Minimum EER2 requirements vary by equipment type, capacity range, and geographic region. For example, the DOE established different minimum thresholds for equipment installed in northern versus southern climate zones. ENERGY STAR certification programs have also updated their criteria to reference EER2 values. It is important to note that local building codes and utility rebate programs may specify EER2 minimums that exceed federal baselines.
Practical Significance
For HVAC professionals, understanding EER2 is essential for code compliance, accurate equipment specification, and meaningful efficiency comparisons between products. Because EER2 numbers are not interchangeable with legacy EER numbers, specifiers must ensure they are referencing the correct metric when reviewing submittals, verifying code compliance, or comparing units from different manufacturers. When evaluating lifecycle operating costs, EER2 provides a more reliable basis for energy consumption estimates because it accounts for the part-load conditions that dominate most cooling seasons. Pairing EER2 analysis with SEER2 and HSPF2 ratings gives a comprehensive picture of year-round system efficiency.