How to Convert EER to COP: Complete Guide 2026

Converting between Energy Efficiency Ratio (EER) and Coefficient of Performance (COP) is essential for HVAC professionals and homeowners comparing equipment efficiency across different regional standards.

The conversion is simple: to convert EER to COP, divide the EER value by 3.413. To convert COP to EER, multiply the COP value by 3.413.

This guide will walk you through everything you need to know about these conversions, from basic definitions to practical applications in real-world scenarios. For more energy efficiency guides, check our comprehensive resources.

Understanding these conversions helps you make informed decisions when purchasing HVAC equipment, calculating energy savings, or comparing products from different regions that use different efficiency standards.

Understanding EER and COP

Before diving into conversions, it’s essential to understand what EER and COP actually measure and how they differ from each other.

What is EER (Energy Efficiency Ratio)?

EER (Energy Efficiency Ratio) measures cooling efficiency as the ratio of cooling output in BTU/h to electrical input in watts. Higher EER means more efficient cooling. This metric is primarily used in the United States and is calculated using the formula: EER = BTU/h ÷ Watts.

For example, an air conditioner with 12,000 BTU/h cooling capacity that consumes 1,200 watts has an EER of 10.0. This rating is tested at specific conditions (95°F outdoor temperature, 80°F indoor temperature, 50% relative humidity), making it a standardized measure for comparing equipment. When evaluating air conditioner efficiency ratings, EER provides a consistent benchmark.

What is COP (Coefficient of Performance)?

COP (Coefficient of Performance) measures energy efficiency as the ratio of heating or cooling output to power input. Higher COP indicates better efficiency. Unlike EER, COP is a unitless ratio that’s commonly used in Europe and other regions outside the United States.

COP is calculated as: COP = Output Energy ÷ Input Energy. For cooling systems, COP represents how many units of cooling energy are produced for each unit of electrical energy consumed. For heating systems, it measures heating output relative to energy input. Heat pumps typically have both heating and cooling COP ratings, which is important when evaluating heat pump efficiency.

Key Differences Between EER and COP

The main difference lies in their units and regional usage. EER uses BTU/watts while COP is unitless. EER is standard in the US market, while COP dominates in European and international markets. This creates the need for conversions when comparing equipment across regions.

Another difference is testing conditions. EER is tested at specific standardized conditions, while COP testing may vary by region and standard. This makes direct comparisons challenging without proper conversions.

EER to COP Conversion Formulas

The conversion between EER and COP is straightforward once you understand the mathematical relationship. The constant 3.413 is the conversion factor between BTU/h and watts (1 watt = 3.413 BTU/h).

EER to COP Formula

To convert EER to COP, use this simple formula: COP = EER ÷ 3.413.

Quick Summary: Divide your EER value by 3.413 to get the equivalent COP. For example, EER 10.0 = COP 2.93.

For example, if you have an air conditioner with EER 10.0: COP = 10.0 ÷ 3.413 = 2.93.

This means the equipment produces 2.93 units of cooling energy for every unit of electrical energy consumed.

COP to EER Formula

To convert COP to EER, reverse the calculation: EER = COP × 3.413.

For example, if you have equipment with COP 3.0: EER = 3.0 × 3.413 = 10.24.

This conversion is useful when comparing European equipment (rated in COP) with American equipment (rated in EER).

Step-by-Step Conversion Process

Identify your starting value: Determine whether you’re converting from EER to COP or COP to EER.
Apply the correct formula: Use division for EER to COP (÷ 3.413) or multiplication for COP to EER (× 3.413).
Round appropriately: Most efficiency ratings are expressed to two decimal places.
Verify your result: Check that your converted value makes sense in the context of typical efficiency ranges.

Conversion Factor: 3.413 is the exact conversion between watts and BTU/h. This constant ensures accurate conversions between EER and COP ratings.

Practical Conversion Examples

Understanding how these conversions apply to real-world equipment helps solidify your knowledge and provides practical reference points for future calculations.

Residential Air Conditioner Example

A typical residential central air conditioner has an EER rating of 11.0. To find the equivalent COP: COP = 11.0 ÷ 3.413 = 3.22.

This means the unit produces 3.22 units of cooling for each unit of electricity consumed. If this same unit were sold in Europe, it would be marketed with a COP rating of 3.22 rather than an EER of 11.0.

Commercial Chiller Example

A commercial water-cooled chiller might have an EER of 15.2. Converting to COP: COP = 15.2 ÷ 3.413 = 4.45.

High-efficiency commercial equipment typically achieves higher EER and COP values than residential equipment due to larger size, more advanced components, and optimized operating conditions.

Heat Pump Example (Cooling Mode)

A heat pump rated at COP 3.5 in cooling mode converts to EER: EER = 3.5 × 3.413 = 11.95.

This conversion is particularly useful when comparing heat pumps from different regions or when trying to understand the equivalent efficiency rating in a different standard.

Energy Savings Calculation Example

When comparing two air conditioners with EER ratings of 10.0 and 12.0, their equivalent COP ratings would be 2.93 and 3.51 respectively. This 0.58 difference in COP represents approximately 18% better efficiency for the higher-rated unit.

For a homeowner running their AC 1,000 hours per year, this efficiency difference could result in significant energy savings. With electricity at $0.15 per kWh, the more efficient unit could save approximately $100-150 annually, depending on cooling load and usage patterns.

Interactive Conversion Calculator

For quick conversions without manual calculations, use this simple reference table for common EER and COP values:

EER Rating	COP Equivalent	Efficiency Level
8.0	2.34	Minimum standard
9.0	2.64	Basic efficiency
10.0	2.93	Good efficiency
11.0	3.22	High efficiency
12.0	3.52	Very high efficiency
13.0	3.81	Premium efficiency
14.0	4.10	Exceptional efficiency
15.0	4.39	Best available

✅ Pro Tip: When comparing equipment, remember that higher EER or COP ratings always indicate better efficiency, regardless of which metric is used.

This table provides quick reference points for common efficiency ratings. For values not shown in the table, use the conversion formulas: COP = EER ÷ 3.413 or EER = COP × 3.413.

Related Efficiency Metrics

While EER and COP are fundamental efficiency metrics, several other ratings are commonly used in the HVAC industry. Understanding these related metrics provides a more complete picture of equipment performance.

SEER (Seasonal Energy Efficiency Ratio)

SEER measures cooling efficiency over an entire cooling season rather than at specific test conditions. SEER values are typically higher than EER values for the same equipment (SEER 14 ≈ EER 11-12). This metric is important for understanding real-world efficiency in residential applications.

kW/ton (Kilowatts per Ton)

This metric expresses power consumption per ton of cooling capacity. To convert from kW/ton to COP: COP = 3.517 ÷ (kW/ton). This conversion is useful for commercial applications where kW/ton is commonly used.

HSPF (Heating Seasonal Performance Factor)

HSPF measures the heating efficiency of heat pumps over an entire heating season. While not directly convertible to EER or COP, HSPF provides similar information for heating performance that COP provides for cooling.

⚠️ Important: Regional efficiency standards vary significantly. The US primarily uses EER and SEER, Europe uses COP and seasonal COP, while other regions may have their own standards.

For more information on specific equipment efficiency, check out our guides on Most Energy Efficient Window ACs and Energy Efficient Water Heaters.

Frequently Asked Questions

Can you convert EER to COP?

Yes, you can convert EER to COP by dividing the EER value by 3.413. For example, an EER of 10.0 converts to a COP of 2.93 (10.0 ÷ 3.413 = 2.93).

Is EER equal to COP?

No, EER and COP are not equal but they measure the same concept (energy efficiency) using different units. EER uses BTU/watts while COP is unitless. The conversion factor between them is 3.413.

What is the relationship between EER and COP?

EER and COP are directly related through the conversion factor 3.413. To convert EER to COP, divide by 3.413. To convert COP to EER, multiply by 3.413. This conversion accounts for the difference between BTU/h and watts.

How to calculate EER from COP?

To calculate EER from COP, multiply the COP value by 3.413. For example, equipment with COP 3.0 would have an EER of 10.24 (3.0 × 3.413 = 10.24).

Why do different regions use different efficiency metrics?

Regional preferences for EER versus COP stem from historical development of standards and measurement systems. The US uses EER with imperial units (BTU), while Europe and other regions use COP with metric units. This creates the need for conversions when comparing equipment internationally.

Final Recommendations

Understanding EER to COP conversions is essential for anyone working with HVAC equipment across different regional standards or comparing products from international markets.

The key takeaway is simple: use the conversion factor 3.413 to convert between these metrics. Divide EER by 3.413 to get COP, or multiply COP by 3.413 to get EER. This mathematical relationship provides accurate conversions for all types of cooling and heating equipment.

When comparing equipment, remember that higher ratings always indicate better efficiency, regardless of which metric is used. Focus on the efficiency difference between options rather than the absolute values, as the relative performance is what matters for energy savings.

For residential applications in the US, focus on EER and SEER ratings. For international equipment or commercial applications, understanding COP becomes increasingly important. Having the ability to convert between these metrics opens up more options when selecting equipment and ensures you’re making informed efficiency comparisons.