Efficiency Standards & Performance Metrics
Understand SEER2, EER, COP, HSPF2, and the ton of refrigeration - the efficiency ratings and performance metrics tested on the EPA 608 exam.
- State the minimum SEER2 ratings for residential AC systems by region as of 2023
- Explain what SEER2 measures and how it differs from the original SEER
- Calculate EER using the standard formula
- Define one ton of refrigeration in BTU/hr
- Explain the Coefficient of Performance (COP) and typical values for air-source heat pumps
- Describe what HSPF2 measures for heating performance
Lección 1
SEER2, EER & Cooling Efficiency Ratings
The Evolution from SEER to SEER2
For decades, the Seasonal Energy Efficiency Ratio (SEER) was the primary metric used to rate the cooling efficiency of residential air conditioners and heat pumps. In January 2023, the U.S. Department of Energy (DOE) transitioned to a new testing standard called SEER2. Understanding both what SEER2 measures and why the change was made is essential for any HVAC technician.
What Is SEER2?
SEER2 (Seasonal Energy Efficiency Ratio 2) measures the seasonal cooling efficiency of an air conditioning system under updated M1 test conditions. It represents the total cooling output in BTU during a typical cooling season divided by the total electrical energy input in watt-hours during that same period.
The formula is:
SEER2 = Total Cooling Output (BTU) / Total Electrical Input (Watt-hours) over an entire cooling season
SEER2 is a seasonal rating, meaning it accounts for the fact that outdoor temperatures vary throughout the cooling season. The system does not always run at full capacity on the hottest day of the year. On milder days, it runs at part load or cycles on and off. SEER2 captures this real-world variation by testing at multiple outdoor temperature conditions and weighting the results to reflect a typical season.
The M1 Test Procedure
The key difference between SEER and SEER2 is the test procedure. The original SEER used a test setup with minimal external static pressure on the ductwork - essentially an idealized, low-resistance installation. The updated M1 test procedure adds a higher external static pressure to simulate more realistic field conditions with actual ductwork, filters, and fittings attached.
Because the M1 test conditions add more realistic resistance (static pressure) to the system, SEER2 numbers are typically slightly lower than the old SEER numbers for the same piece of equipment. A system that was rated 14 SEER under the old test might rate around 13.4 SEER2 under the new test. The equipment did not get less efficient - the test just became more realistic.
Minimum SEER2 Requirements by Region (2023)
As of January 1, 2023, the DOE established new minimum efficiency standards for residential central air conditioners and heat pumps. These minimums vary by geographic region:
| Region | Minimum SEER2 |
|---|---|
| North (states in the northern climate zone) | 13.4 SEER2 |
| South (states in the southern climate zone, including the Southeast and Southwest) | 14.3 SEER2 |
The southern region has a higher minimum because cooling demand is greater in hot climates. Systems in the South run more hours per year, so higher efficiency standards yield more significant energy savings over the equipment's lifetime.
The DOE defines the boundary between North and South regions. Generally, states like Alabama, Arizona, Arkansas, California (in part), Florida, Georgia, Hawaii, Louisiana, Mississippi, Nevada, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia (in part) fall in the South region. Northern states include the remainder.
For the exam, remember: 13.4 SEER2 (North) and 14.3 SEER2 (South) are the minimum residential AC efficiency standards as of 2023.
What Is EER?
While SEER2 measures seasonal efficiency across varying conditions, EER (Energy Efficiency Ratio) measures efficiency at a single set of specific conditions. It provides a snapshot of how efficiently the system operates at peak load.
The EER formula is straightforward:
EER = BTU/hr of cooling output / Watts of electrical input
For example, if an air conditioner produces 36,000 BTU/hr of cooling and consumes 3,000 watts of electricity:
EER = 36,000 / 3,000 = 12.0 EER
The standard ARI (now AHRI) conditions for EER testing are:
- Outdoor temperature: 95 degrees F
- Indoor dry-bulb: 80 degrees F
- Indoor wet-bulb: 67 degrees F
EER is useful for comparing equipment performance under peak conditions. A system with a higher EER will use less electricity on the hottest days of the year when the electrical grid is most stressed.
Key Differences Between SEER2 and EER
| Feature | SEER2 | EER |
|---|---|---|
| What it measures | Seasonal (whole-season) efficiency | Efficiency at one specific condition |
| Test conditions | Multiple outdoor temps, weighted average, M1 static pressure | Single outdoor temp (95°F), standard conditions |
| Units | BTU / Watt-hour (seasonal totals) | BTU/hr / Watts (instantaneous) |
| Best used for | Comparing annual operating costs | Comparing peak-load performance |
SEER2 - Seasonal Efficiency
Measures total cooling output over an entire season divided by total energy used. Tested under the M1 procedure with realistic static pressure. Best for comparing annual operating costs across equipment.
EER - Peak-Load Efficiency
Measures cooling output at one specific outdoor condition (95°F). A snapshot of performance on the hottest day. Best for comparing how equipment handles extreme heat loads.
HSPF2 - Heating Efficiency
Measures total heating output over an entire heating season divided by total energy used. Accounts for defrost cycles and supplemental heat. The heating counterpart to SEER2.
Why Both Ratings Matter
SEER2 is the better predictor of annual energy costs because it accounts for the full range of operating conditions throughout the season. However, EER matters in hot climates where the system runs at or near full capacity for extended periods. A system with a high SEER2 but mediocre EER may not perform well in extreme heat. Utility companies in hot climates sometimes offer rebates based on EER rather than SEER2.