Formula & Calculator
SEER to EER Conversion (Air Conditioner Efficiency)
This calculator helps you convert Seasonal Energy Efficiency Ratio (SEER) to Energy Efficiency Ratio (EER) for air conditioners and heat pumps. SEER measures cooling efficiency over an entire cooling season, while EER measures efficiency at a specific outdoor temperature (typically 35°C). The conversion is important when comparing AC units or estimating performance under peak load conditions. The tool provides a simple linear conversion and a more accurate quadratic formula based on industry standards (AHRI).
Common SEER → EER Reference (Quadratic)
| SEER | EER (Quadratic) | EER (Linear) | Efficiency Category |
|---|
Interpretation
Understanding the difference between SEER and EER is important for anyone buying, selling, or operating air conditioning equipment.
SEER (Seasonal Energy Efficiency Ratio) – measures cooling output divided by total electric energy input over a typical cooling season. It is a weighted average that reflects varying outdoor temperatures. In the United States, the minimum SEER for new units is 13 or 14, with high-efficiency units reaching 20 or more.
EER (Energy Efficiency Ratio) – measures cooling output divided by power input at a specific set of conditions: outdoor temperature of 95°F (35°C), indoor temperature of 80°F (27°C), and 50% relative humidity. It is a snapshot of performance under peak load.
The approximate relationship is: EER ≈ SEER × 0.875. However, this linear relationship breaks down for very high SEER values, because high-SEER units often use advanced compressors and heat exchangers that do not scale linearly. The quadratic formula provided in this calculator: EER = -0.02 × SEER² + 1.12 × SEER - 0.5, is a better fit for modern equipment.
When comparing units, remember that a higher SEER means lower operating costs over the entire season, but a higher EER means better performance on the hottest days. If you live in a very hot climate, you may want to prioritise EER over SEER. In milder climates, SEER is more important.
This calculator helps you quickly convert between these ratings so you can evaluate both seasonal and peak performance, making your HVAC decisions more informed.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| SEER | Seasonal Energy Efficiency Ratio | Btu/Wh |
| EER | Energy Efficiency Ratio | Btu/Wh |
| Conversion Factor | Approximate multiplier | 0.875 (linear) or quadratic formula |
What it means
SEER and EER are both measures of air conditioner efficiency, but they are calculated under different conditions. SEER is an average over an entire cooling season, accounting for varying outdoor temperatures. EER is a single-point measurement at a high outdoor temperature (35°C). Because of this, SEER values are typically higher than EER values for the same unit. The conversion between them helps you understand how your air conditioner will perform on the hottest days of the year. This calculator gives you two conversion methods: a simple linear rule of thumb and a more accurate quadratic formula based on industry data. The linear method is quick and easy, while the quadratic method better reflects real-world performance for modern high-SEER units. Use this tool to make better comparisons and decisions for your cooling needs.
Worked example
Example 1 – Mid‑Efficiency AC (SEER 16)
Real‑World| Parameter | Value |
|---|---|
| SEER | 16.0 |
| Conversion Method | Quadratic (Precise) |
| Formula | EER = −0.02·SEER² + 1.12·SEER − 0.5 |
Example 2 – High‑Efficiency AC (SEER 22)
Premium| Parameter | Value |
|---|---|
| SEER | 22.0 |
| Linear Method | EER = 22 × 0.875 = 19.25 |
| Quadratic Method | EER = −0.02·22² + 1.12·22 − 0.5 = 15.66 |
Common mistakes
- Assuming SEER and EER are the same – they are not; SEER is always higher than EER.
- Using the wrong conversion factor – the 0.875 factor is an approximation; actual conversion depends on the specific unit and test conditions.
- Forgetting that SEER is a seasonal average, while EER is a fixed-temperature rating.
- Using the linear formula for all units – the quadratic formula is more accurate for very high SEER units.
- Not checking the manufacturer's data for the exact EER rating, which is always the most reliable.
- Confusing units – both are measured in Btu per watt-hour, but the test conditions differ.
- Applying the conversion backwards (converting EER to SEER with the same factor) – SEER ≈ EER × 1.14, not 0.875.
Applications
- Compare air conditioner efficiency ratings when shopping for a new unit.
- Estimate peak-load performance to size cooling systems properly.
- Understand how seasonal efficiency translates to real-world operation.
- Evaluate energy savings and operating costs for different AC models.
- Help HVAC technicians and engineers design efficient cooling systems.
- Convert SEER ratings from product labels to EER for technical specifications.
- Make informed decisions about upgrading or replacing existing units.
- Analyse the trade-off between seasonal efficiency and peak performance.
Frequently Asked Questions
SEER stands for Seasonal Energy Efficiency Ratio. It measures how efficiently an air conditioner or heat pump cools over an entire cooling season. It is calculated by dividing the total cooling output (in Btu) by the total energy input (in watt-hours) over a range of outdoor temperatures.
EER stands for Energy Efficiency Ratio. It measures cooling efficiency at a single, steady-state condition – typically 95°F (35°C) outdoor temperature. It is calculated as cooling output (Btu) divided by power input (watts) at that specific temperature.
Because SEER is averaged over a season with many moderate-temperature days, during which the unit operates more efficiently. EER is measured at a high temperature, where efficiency drops. Hence, SEER is usually about 10-20% higher than EER for the same unit.
A common rule of thumb is EER = SEER × 0.875. However, this is an approximation. More accurate conversions use quadratic formulas that depend on the specific SEER value, as high-SEER units have different performance characteristics.
Yes, roughly SEER = EER × 1.14. But this is also an approximation. The exact relationship varies by unit design and test conditions. Always check the manufacturer's data for precise ratings.
In very hot climates, EER is more important because the unit will spend more time operating at peak conditions. In milder climates, SEER is a better indicator of overall seasonal performance.
For new residential units, a SEER of 14-16 is standard, 18-20 is high efficiency, and above 20 is premium. The minimum required varies by region.
EER values typically range from 8 to 14 for residential units. Higher EER means better performance at peak temperatures. An EER of 12 or above is considered excellent.
Most modern units have a SEER rating. EER is often listed as well, especially in technical specifications. Some older units may only have EER.
The linear conversion (0.875) is a rough estimate. For units with SEER between 13 and 18, it works reasonably well. For very high SEER units (20+), the quadratic formula gives a better result.
Look at the manufacturer's data plate or technical specification sheet. The AHRI (Air-Conditioning, Heating, and Refrigeration Institute) directory also provides certified ratings.
Yes, the same principles apply to heat pumps in cooling mode. However, heat pumps also have heating efficiency ratings like HSPF, which are different.
Both are measured in British thermal units per watt-hour (Btu/Wh). This is a ratio of cooling output to energy input.
Yes, higher SEER means lower operating costs. However, higher SEER units cost more upfront, so you should consider the payback period based on your climate and usage.
Yes, the conversion principles apply to commercial units as well. However, commercial units often have different test conditions and may have separate IPLV (Integrated Part-Load Value) ratings.
SEER2 is a newer test procedure that better reflects real-world conditions, with slightly different testing parameters. SEER2 values are typically about 5% lower than SEER for the same unit.
The conversion factors may differ slightly for SEER2. As a rough guide, you can use the same formulas but note that SEER2 values are lower, so the resulting EER will also be slightly lower.
A quick rule: EER ≈ SEER × 0.9 (for SEER up to 18) and EER ≈ SEER × 0.85 (for higher SEER). But the calculator gives more accurate results.
Yes, duct losses can reduce the effective efficiency. Both SEER and EER are measured under ideal lab conditions; actual performance may be lower in real installations.
Yes, window units also have EER ratings (they often do not have SEER). You can use the calculator to estimate SEER from EER or vice versa, but note that window units are typically less efficient than central systems.