EER to SEER Conversion: Complete Guide with Formula and Chart

EER vs SEER: Understanding the Difference

Before diving into conversions, it's important to understand what each rating measures and why both exist. Both are important metrics covered in our SEER Rating Chart.

What Is EER?

EER (Energy Efficiency Ratio) measures an air conditioner's efficiency at a specific operating condition: when the outdoor temperature is exactly 95°F, the indoor temperature is 80°F, and relative humidity is 50%. This represents a peak cooling scenario on a hot summer day.

The EER formula is straightforward:

For example, an AC unit that produces 36,000 BTU/hour of cooling while drawing 3,000 watts has an EER of 12 (36,000 ÷ 3,000 = 12).

What Is SEER?

SEER (Seasonal Energy Efficiency Ratio) measures efficiency across an entire cooling season, accounting for varying outdoor temperatures from 65°F to 104°F. This provides a more realistic picture of how the unit performs throughout summer, not just on the hottest days.

The SEER formula is conceptually similar but uses seasonal totals:

Because air conditioners operate more efficiently at lower outdoor temperatures, SEER ratings are typically higher than EER ratings for the same unit. The AC runs less hard when it's 75°F outside compared to when it's 95°F.

Why Both Ratings Exist

Each rating serves a different purpose:

• EER: Best for evaluating performance in consistently hot climates where the AC often runs at peak conditions (Arizona, Nevada, Texas Gulf Coast)
• SEER: Best for evaluating average seasonal performance in climates with varying summer temperatures (most of the US)

Federal regulations from the U.S. Department of Energy use SEER for minimum efficiency standards, but EER remains important for commercial applications and hot-climate residential decisions.

The EER to SEER Conversion Formula

While there's no exact mathematical conversion between EER and SEER (because they measure different things), there's a widely-used approximation based on typical residential AC performance:

This means SEER is approximately 12% higher than EER for most residential central air conditioners. The conversion works in both directions:

• EER to SEER: Multiply EER by 1.12
• SEER to EER: Divide SEER by 1.12 (or multiply by 0.893)

Example Conversions

Converting EER to SEER:

• EER 10 → SEER ≈ 10 × 1.12 = 11.2
• EER 12 → SEER ≈ 12 × 1.12 = 13.4
• EER 14 → SEER ≈ 14 × 1.12 = 15.7

Converting SEER to EER:

• SEER 14 → EER ≈ 14 ÷ 1.12 = 12.5
• SEER 16 → EER ≈ 16 ÷ 1.12 = 14.3
• SEER 20 → EER ≈ 20 ÷ 1.12 = 17.9

Limitations of the 1.12 Factor

The 1.12 conversion factor is an approximation that works well for most residential split-system air conditioners. However, the actual relationship varies based on:

• Compressor type: Variable-speed units may have different EER/SEER relationships than single-stage units
• Unit size: Larger units may have slightly different efficiency curves
• Design specifics: Different manufacturers optimize differently
• Operating conditions: Actual installed conditions affect real-world performance

For precise values, always refer to the manufacturer's published specifications, which list both EER and SEER for each model.

EER to SEER Conversion Chart

The following chart provides quick reference conversions between EER and SEER ratings. These are approximate values based on the 1.12 conversion factor.

Note: These are approximate conversions. Actual manufacturer specifications may vary. For precise ratings, consult product documentation.

Comprehensive EER to SEER & SEER2 Conversion Table

The following expanded table includes SEER2 equivalents (using the 1.07 factor) and estimated annual operating costs for a 3-ton system running 1,500 hours at $0.15/kWh, helping you compare efficiency across all three rating systems.

*Estimated annual cost based on 3-ton system, 1,500 cooling hours/year, $0.15/kWh. Actual costs vary by usage, climate, and electricity rates. For precise ratings, consult the AHRI Directory.

SEER to EER Conversion Chart

For convenience, here's the reverse conversion chart from SEER to EER:

Use Our EER to SEER Converter

For quick and accurate conversions, use our EER to SEER Converter. Simply enter your known value and select the conversion direction. The calculator instantly provides the converted rating plus additional context about what that efficiency level means.

The converter handles both directions:

• Enter an EER value to get the equivalent SEER
• Enter a SEER value to get the equivalent EER

This is particularly useful when comparing window AC units (which often emphasize EER) with central AC systems (which emphasize SEER).

When to Use EER vs SEER

Understanding when each rating is more relevant helps you make better equipment decisions.

When EER Matters More

Focus on EER in these situations:

• Consistently hot climates: Phoenix, Las Vegas, Palm Springs, and similar desert locations where outdoor temperatures frequently exceed 95°F
• Window air conditioners: Window units are often rated by EER (or CEER) rather than SEER. Search for rated models at the ENERGY STAR room AC product finder
• Commercial applications: Commercial buildings often use EER for equipment comparisons
• Peak demand concerns: If you're worried about performance on the hottest days specifically
• Utility demand charges: Commercial customers with demand charges care about peak power draw

When SEER Matters More

Focus on SEER in these situations:

• Most residential applications: SEER is the standard for comparing central AC systems. See our savings calculator guide for how SEER affects your energy costs.
• Variable climates: If summer temperatures fluctuate significantly (most of the US)
• Seasonal cost estimates: SEER better predicts your total cooling season electricity use
• Meeting regulations: Federal minimum standards are expressed in SEER
• Rebate programs: Most utility rebates specify SEER thresholds

Consider Both When Possible

The most complete evaluation considers both ratings. A high SEER with a relatively low EER suggests the unit excels at moderate conditions but may struggle on the hottest days. Conversely, a high EER with modest SEER indicates strong peak performance but less efficiency during mild weather.

Variable-speed units typically perform well on both metrics because they can modulate output to match conditions efficiently.

Alternative Conversion Formulas

While the 1.12 multiplier is most common, you may encounter other conversion approaches:

DOE Simplified Formula

The Department of Energy has published guidelines suggesting:

This quadratic formula accounts for diminishing returns at higher efficiency levels. However, the difference from the simple 1.12 multiplier is typically less than 0.5 SEER points for residential units, so the simple formula is adequate for most purposes.

Manufacturer-Specific Ratios

Some manufacturers provide specific EER/SEER ratios for their product lines. These may range from 1.10 to 1.15 depending on the technology used. When comparing units within a single manufacturer's lineup, their published specifications are more accurate than generic formulas.

IEER for Commercial Equipment

Commercial air conditioning equipment uses IEER (Integrated Energy Efficiency Ratio), which accounts for part-load performance. IEER is calculated differently than SEER and shouldn't be directly converted using the 1.12 factor. IEER typically falls between EER and SEER in numerical value.

EER and SEER for Different Equipment Types

Different types of cooling equipment have characteristic EER/SEER relationships:

Central Air Conditioners

Traditional split-system central ACs closely follow the 1.12 conversion factor. Most residential units today range from:

• EER: 11-16
• SEER: 14-26

Heat Pumps

Heat pumps have similar EER/SEER ratios to central ACs for their cooling mode. However, they also have heating efficiency ratings (HSPF and COP) that don't relate to EER/SEER.

Window Air Conditioners

Window units are typically rated using CEER (Combined Energy Efficiency Ratio), which includes standby power consumption. CEER is similar to EER but slightly lower due to standby losses. For conversion purposes, treat CEER like EER.

Ductless Mini-Splits

Mini-split systems often achieve very high SEER ratings (20-33+) due to their variable-speed inverter compressors. Their EER/SEER ratio may be slightly higher than 1.12 because inverter technology performs exceptionally well at part-load conditions that SEER emphasizes.

Packaged Units

Packaged units (rooftop or through-wall) containing all components in one cabinet tend to have lower efficiency than split systems. Their EER/SEER ratio is typically close to the 1.12 standard.

Historical Context of EER and SEER

Understanding the history of these ratings provides context for older equipment:

The Era of EER Only (Pre-1979)

Before SEER was introduced, only EER was used to rate air conditioners. Units from this era often had EER ratings of 5-8, equivalent to about 6-9 SEER by modern standards.

Introduction of SEER (1979)

The Department of Energy introduced SEER as a more representative measure of seasonal performance. Both ratings have been used in parallel since then, with SEER becoming the primary metric for regulatory purposes.

Minimum Standards Evolution

Federal minimum SEER requirements have increased over time:

• 1992: 10 SEER minimum (≈ 9 EER)
• 2006: 13 SEER minimum (≈ 11.6 EER)
• 2015: 13-14 SEER by region (≈ 11.6-12.5 EER)
• 2023: 14-15 SEER by region (≈ 12.5-13.4 EER)

SEER2 Introduction (2023)

In 2023, SEER2 testing standards were introduced, using more rigorous conditions that better represent real-world installations. Our guide on SEER vs SEER2 Explained covers this transition in detail. SEER2 ratings are approximately 4.5% lower than equivalent SEER ratings. When converting from EER, you can use:

Practical Applications of EER/SEER Conversion

Here are real-world scenarios where converting between EER and SEER proves useful:

Comparing Window AC to Central AC

You might be deciding between a high-efficiency window unit (rated by EER) and upgrading to central air (rated by SEER). Converting to a common metric allows fair comparison of efficiency. Use our SEER recommendation guide to determine the right efficiency for your home.

Example: A window unit rated EER 12 compares to a central AC rated approximately 13.4 SEER. If the central AC you're considering is 16 SEER, it's about 19% more efficient at seasonal average conditions.

Evaluating International Equipment

Equipment manufactured for markets outside the US may use EER or other metrics. Converting to SEER helps compare with domestic options and understand regulatory compliance.

Understanding Older Specifications

Older equipment documentation may emphasize EER. Converting to SEER helps compare legacy equipment to modern options and estimate potential savings from upgrading.

Commercial to Residential Comparison

If you're familiar with commercial HVAC (which uses EER) and transitioning to residential decisions (which use SEER), conversion helps translate your knowledge.

Energy Cost Implications

Understanding EER and SEER helps predict energy costs in different scenarios:

Using EER for Peak Day Costs

To estimate electricity cost on a very hot day when your AC runs continuously:

Example: A 36,000 BTU unit with EER 12, running 12 hours:

Peak Day kWh = (36,000 × 12) ÷ (12 × 1,000) = 36 kWh

At $0.15/kWh, that's $5.40 for one hot day's cooling.

Using SEER for Seasonal Costs

To estimate total cooling season electricity cost:

Example: Same 36,000 BTU unit with SEER 13.4 (equivalent to EER 12), running 1,500 hours per season:

Seasonal kWh = (36,000 × 1,500) ÷ (13.4 × 1,000) = 4,030 kWh

At $0.15/kWh, that's $604 for the cooling season.

Upgrade Savings Example

Upgrading from EER 10 (≈ 11.2 SEER) to EER 14 (≈ 15.7 SEER) for the same 3-ton system:

• Old annual cost: (36,000 × 1,500) ÷ (11.2 × 1,000) × $0.15 = $723
• New annual cost: (36,000 × 1,500) ÷ (15.7 × 1,000) × $0.15 = $516
• Annual savings: $207

Frequently Asked Questions

Is a higher EER always better?

Higher EER means better peak efficiency, but it doesn't guarantee lower total energy costs. SEER is usually more relevant for total seasonal costs. However, in consistently hot climates where the AC often runs at peak conditions, EER becomes more predictive of actual performance.

Why is my unit's actual EER/SEER ratio different from 1.12?

The 1.12 factor is an industry average. Individual units may vary based on compressor technology, refrigerant type, and design optimization. Variable-speed units, in particular, may have higher ratios because they excel at the part-load conditions that SEER emphasizes.

Can I use EER to qualify for SEER-based rebates?

Generally, no. Utility rebates and federal tax credits specify SEER thresholds and require documentation of the actual SEER rating, not a converted estimate. However, if a unit meets a SEER threshold, it will have a proportionally high EER as well.

Does EER or SEER matter for heat pump heating mode?

Neither. EER and SEER only measure cooling efficiency. Heating efficiency is measured by HSPF (Heating Seasonal Performance Factor) or COP (Coefficient of Performance).

Are SEER2 and EER2 related?

Yes. The 2023 testing standard updates apply to both metrics, resulting in SEER2 and EER2. The relationship between them is similar to SEER/EER, but the absolute numbers are slightly lower due to more stringent testing conditions.

Conclusion

Converting between EER and SEER allows you to compare different equipment specifications and understand air conditioner efficiency from multiple perspectives. While the 1.12 conversion factor provides a good approximation, remember that:

• EER measures peak efficiency at 95°F outdoor temperature
• SEER measures seasonal average efficiency across varying temperatures
• SEER is typically about 12% higher than EER for the same unit
• Both ratings matter - EER for hot climates, SEER for seasonal costs
• For precise values, always consult manufacturer specifications
• Variable-speed units may have different EER/SEER relationships

Use our EER to SEER Converter for quick conversions, and our SEER Calculator to estimate energy savings when upgrading to a more efficient system. For further reading, explore our SEER Rating Chart for a full efficiency reference, the HVAC Efficiency Calculator Guide for all efficiency metrics, and our Heat Pump SEER Ratings guide if you are considering a heat pump.

Sources & References

• U.S. Department of Energy - Central Air Conditioning - Federal standards explaining EER and SEER metrics
• AHRI Directory - Official certification database with both EER and SEER ratings for all certified equipment
• ENERGY STAR - EPA and DOE program for identifying high-efficiency cooling products
• ASHRAE - American Society of Heating, Refrigerating and Air-Conditioning Engineers, developers of testing standards
• EIA Electricity Monthly - U.S. electricity consumption and pricing data for cost calculations