EER vs SEER vs SEER2

Glossary By Jessica Navarro

In this article, we'll uncover the following topics:

What is EER?

EER (Energy Efficiency Ratio) is a measure of how efficiently an air conditioner operates at a specific outdoor temperature – typically 35°C (95°F).

EER = Cooling capacity (BTU/hr) ÷ Power input (watts)

A higher EER means greater efficiency. For example, an enclosure air conditioner with an EER of 10 delivers 10 BTU/hr of cooling for every watt of electricity consumed. (Read more on how to calculate BTUs for enclosure cooling)

What is SEER?

SEER (Seasonal Energy Efficiency Ratio) is an average efficiency measurement over a full cooling season, based on a range of outside temperatures and part-load conditions.

SEER = Total seasonal cooling output ÷ Total seasonal energy input

SEER provides a more realistic picture of performance in climates where temperatures vary. It’s the standard rating used for residential HVAC units, but it’s also applicable to larger telecom or industrial cooling systems.

What is SEER2?

SEER2 is the updated version of SEER, introduced by the U.S. Department of Energy (DOE) in 2023 to reflect stricter, real-world testing procedures. It accounts for:

External static pressure
Duct losses
System installation variables

As a result, SEER2 ratings are generally lower than SEER, even for the same system — but they offer a more realistic picture of actual energy performance.

SEER2 = Updated Seasonal Output ÷ Updated Seasonal Energy Input
(testing includes 5x more external static pressure than SEER)

Factor	EER	SEER	SEER2
Comparison table: EER vs SEER vs SEER2
Measurement type	Fixed temp (typically 35°C/95°F)	Seasonal average (13°C–35°C)	Seasonal, with added system pressure
Use case	Industrial, enclosures, telecom	Residential, seasonal use	Regulatory & real-world comparison
Test condition	100% full-load	Partial-load, lab settings	Partial-load + duct pressure losses
Energy profile	Peak performance only	Average seasonal performance	Realistic seasonal performance
Typical values	9–12	13–20+	11.7–16+ (approx. 4.75% lower than SEER)
Ideal for	Hot, consistent climates	Variable climates	Compliance, realistic performance

SEER2 is now required on most new AC systems sold in the U.S. and is being adopted globally as a more accurate benchmark for efficiency.

In many technical applications (like cabinet cooling systems or off grid telecom sites) both EER and SEER provide useful perspectives on how a system will perform under real-world electrical loads and outdoor conditions.

Why energy efficiency ratios matter in industrial cooling

The energy efficiency of an air conditioner plays a major role in both cooling performance and operating cost. Understanding EER and SEER and how each is calculated helps you choose the right cooling system for your application, whether it’s an electrical enclosure, outdoor telecom cabinet, or building HVAC system.

Choosing the right ratio ensures:

Lower energy bills
Smaller carbon footprint
Extended backup power runtime
Regulatory compliance in U.S., EU, and other regions

In cabinet cooling systems, where uptime is mission-critical, small gains in efficiency translate to long-term operational savings and improved sustainability. And in remote or off grid environments, higher EER systems can even prolong battery runtime or reduce generator usage.

Frequently asked questions (FAQ)

For constant-load or high-temperature environments (e.g., industrial enclosures), focus on EER.
For seasonal systems, consider SEER and SEER2.
For compliance and real-world insights, SEER2 is now the most relevant.

An EER of 9–12 is typical for industrial units, while premium systems may exceed 12.
For residential or seasonal systems, a SEER rating of 14-16 is standard, while 18+ is considered high efficiency.
A SEER2 of 13.4 or higher (in the U.S. South) meets current federal requirements. High-efficiency models may range from 14.3 to 16+, depending on system type.

SEER2 uses stricter testing, simulating real-world duct losses and pressure, so values appear lower, but they’re more accurate.

Some do, especially if they’re designed for telecom shelters or climate-sensitive regions. But EER is more common for enclosure and cabinet cooling systems.

There’s no exact formula, but SEER ≈ EER × 1.1 to 1.2 is a rough rule of thumb, depending on usage and part-load conditions.

Not always. A high EER is useful in hot, continuous-load applications, but other factors like airflow design, maintenance access, and NEMA/IP ratings may also affect overall system performance.

Often yes – but the upfront cost is usually offset by long-term energy savings, especially in systems that run 24/7 or in off grid power setups.