About SEER2
“SEER2” stands for Seasonal Energy Efficiency Ratio 2. Specifically, SEER2 is the total heat removed from the conditioned space during the annual cooling season. The new M1 testing procedure 
will increase systems' external static pressure by a factor of five to better reflect field conditions of installed equipment. With this change, new nomenclature will be used to denote M1 ratings (including EER2 and HSPF2 ).
M1 Testing Requirements
To meet new testing requirements, manufacturers are redesigning system components. In fact, all air conditioning and heat pump systems must be renovated by January 1, 2023, even if they meet current SEER ratings. In addition, matching components such as furnaces and air handlers will be redesigned to meet changes in the airflow setpoint. Depending on your region, additional field install equipment, such as Thermal Expansion Valves (TXVs), may also be required.
M1 Testing Procedures
The goal of new SEER2 testing procedures is to better represent external conditions seen in the field. Current SEER testing does not accurately emulate the influence of ductwork and external static pressure on HVAC products. Because of this, it is not often representative of real-world applications. By increasing systems’ external static pressure from current SEER (0.1 in. of water) to SEER2 (0.5 in. of water), new M1 testing procedures more accurately reflect current field conditions.
