The transition from SEER (Seasonal Energy Efficiency Ratio) to SEER2 represents an update in the methodology for measuring the efficiency of air conditioning and heat pump systems. Both are metrics that homeowners, especially in varied climates like Philadelphia, should understand when considering HVAC upgrades or replacements. Here’s a breakdown of the differences and what they mean for you.

SEER: The Original Efficiency Standard

SEER measures the cooling output of an air conditioner or heat pump over a typical cooling season, divided by the energy it consumes in Watt-Hours. It's calculated using a constant indoor temperature and a range of outdoor temperatures from 60°F to 100°F. This rating provides a baseline indication of a unit's efficiency under optimal conditions.

SEER2: A More Stringent and Realistic Measure

SEER2, which stands for Seasonal Energy Efficiency Ratio 2, is a new standard that was introduced to provide a more accurate reflection of operational efficiency under typical field conditions rather than laboratory conditions. SEER2 ratings are generally lower than SEER ratings for the same unit because the testing conditions are more stringent:

  1. Higher External Static Pressure: SEER2 tests HVAC systems at a higher external static pressure to better mimic real-world, installed conditions. This addresses the efficiency drops that occur due to factors like ductwork resistance.

  2. Adjusted Temperature Ranges: The temperature ranges used for SEER2 calculations are slightly adjusted to better reflect average seasonal temperatures during the cooling season.

  3. Fan Energy Consumption: SEER2 includes the energy used by the blower fan in the efficiency calculation, which is a significant factor in overall energy use.

Impact of SEER vs. SEER2 on Homeowners

For homeowners in Philadelphia, understanding the shift from SEER to SEER2 is crucial when comparing new HVAC systems:

  • Lower SEER2 Ratings: When comparing new systems, note that a unit with a SEER2 rating will have a lower number than what its SEER rating would suggest. However, this doesn't mean it's less efficient; it's just measured more rigorously.

  • Regulatory Compliance: As of January 2023, new federal regulations require HVAC systems to meet SEER2 standards. In the Northern U.S., including Pennsylvania, the minimum SEER2 ratings for air conditioners are slightly lower than the SEER ratings. For example, what used to be a minimum SEER of 14 might now be around a SEER2 of 13.4.

  • Consider Total Cost of Ownership: While SEER2-rated units might be more expensive due to enhanced technology, they potentially offer greater energy savings over time due to their more realistic performance metrics.


When upgrading or installing new HVAC units in Philadelphia, consider both the SEER and SEER2 ratings. Although SEER2 represents a more stringent and realistic measure of efficiency, the choice between different models and types should also consider other factors like unit size, your home’s insulation, and overall HVAC system design. Consulting with a knowledgeable HVAC provider like McCorry Comfort can help ensure that your new system is not only compliant with current standards but also tailored to your specific needs for maximum comfort and efficiency.