SEER2 Ratings Explained

SEER2 stands for Seasonal Energy Efficiency Ratio 2. It measures how efficiently an air conditioning system converts electricity into cooling over an entire cooling season. The rating is calculated by dividing the total cooling output in BTUs over a season by the total electrical energy input in watt-hours over the same season. A higher SEER2 number means the system uses less electricity to produce the same amount of cooling. SEER2 replaced the original SEER metric in January 2023. The key difference is that SEER2 is tested under conditions that better reflect real-world installation, specifically using higher static pressure in the duct system.

The original SEER test used an unrealistically low duct pressure that inflated efficiency numbers. SEER2 testing uses a more realistic pressure drop, which means SEER2 numbers are approximately 5 to 10 percent lower than the equivalent SEER numbers for the same equipment. A system that was rated 16 SEER under the old standard might be rated 15.2 SEER2 under the new standard, even though the system itself has not changed. This is important to understand when comparing older efficiency ratings you may find online with current SEER2 ratings. The minimum SEER2 standard varies by region. For Nashville and the entire Southeast region, the minimum is 14.3 SEER2, equivalent to approximately 15 SEER under the old system.

No new air conditioning system installed in Nashville can have a SEER2 rating below 14.3.

The SEER2 rating is closely related to the compressor type because the compressor technology determines how efficiently the system operates across varying conditions. Single-stage systems have compressors that are either fully on or fully off. They operate at maximum capacity every time they run, regardless of whether the outdoor temperature is 85 degrees or 105 degrees. They cycle on and off frequently, especially on milder days when the full cooling capacity quickly satisfies the thermostat. Single-stage systems are the least expensive and typically rated at 14.3 to 16 SEER2. Two-stage systems have compressors with two operating speeds, typically 70 percent and 100 percent capacity.

On moderately warm days, the system runs at the lower, more efficient stage for longer periods, providing better dehumidification and more even temperatures. It ramps up to full capacity only on the hottest days. Two-stage systems typically rate at 16 to 19 SEER2 and represent the sweet spot of efficiency and value for most Nashville homeowners. Variable-speed or inverter-driven systems can operate at any capacity from approximately 25 percent to 100 percent. They continuously adjust output to match the exact cooling demand, running at lower, more efficient speeds most of the time. This produces the most consistent temperatures, the best humidity control, the quietest operation, and the highest SEER2 ratings, typically 20 to 24+ SEER2.

Variable-speed systems cost more upfront but provide the best comfort and the lowest operating costs. The key insight is that SEER2 is a seasonal average. A variable-speed system achieves a high SEER2 because it runs at efficient low speeds most of the time, not because it is more efficient at full capacity. If you live in Nashville and set your thermostat to 75 degrees, a variable-speed system might run at 40 percent capacity for 18 hours on a 90-degree day instead of cycling on and off every 15 minutes at full blast.

SEER2 is the primary cooling efficiency rating, but you may encounter other ratings that measure different aspects of system performance. EER2, or Energy Efficiency Ratio 2, measures efficiency at a single outdoor temperature, typically 95 degrees, rather than across a range of seasonal temperatures. EER2 is a better indicator of peak-demand performance, which is relevant for Nashville because we experience many days above 95 degrees. A system with a high SEER2 but mediocre EER2 may be efficient at moderate temperatures but less efficient on the hottest days. HSPF2, or Heating Seasonal Performance Factor 2, measures heating efficiency for heat pump systems.

It is the heating equivalent of SEER2 and is important if you are considering a heat pump for year-round heating and cooling. Higher HSPF2 means less electricity used for heating. The minimum HSPF2 for the Southeast region is 7.5. AFUE, or Annual Fuel Utilization Efficiency, measures gas furnace efficiency as a percentage. An 80 percent AFUE furnace converts 80 percent of the gas it burns into heat, with 20 percent lost up the flue. High-efficiency furnaces achieve 96 to 98 percent AFUE. This rating is relevant if you have a gas furnace paired with your AC system. CEE tiers are efficiency levels defined by the Consortium for Energy Efficiency.

Higher CEE tiers qualify for additional rebates from some utilities. We identify the CEE tier of recommended equipment and check for any applicable rebate programs during your consultation.