SEER Vs SEER2 Rating: What’s The Difference? (+ Implications)

Starting in 2023, a lot of people started asking us what is the difference between SEER and SEER2 ratings. This surge in interest in the SEER2 rating is understandable. From 1st January 2023, all new HVAC units started listing SEER2 rating on their specs sheets.

Here’s why we see a lot of these SEER vs SEER2 rating questions:

  • We are used to SEER rating. The legislature introducing the SEER rating was passed in 1987, and we started using it in 1992.
  • SEER2 rating is mostly unfamiliar to us. This is the new SEER rating; the legislature was introduced in 2016, and it became a policy we are going to use from 1st January 2023 on. Here is the original 268-page SEER2 document titled ‘Energy Conservation Program: Energy Conservation Standards for Residential Central Air Conditioners and Heat Pumps’. To understand the SEER2 rating and how it relates to the SEER rating, we have to boil down the differences specified in this document.

Now, both SEER and SEER2 are energy efficiency ratings for HVAC units (primarily air conditioners and heat pumps).

seer2 vs seer in heat pumps and air conditioners
The main determinant of a heat pump or AC efficiency is the outdoor units that houses the all-important compressor.

A lot of questions we are going to address started arising around this new 2023 SEER rating, including:

“Are SEER and SEER2 the same?”

“What is SEER2 in HVAC?”

“Why is SEER2 lower than SEER?”

Quick example we see in 2023 HVAC specs sheets: A 14 SEER heat pump is now a 13.4 SEER2 heat pump.

We immediately see that SEER and SEER2 are not the same. Clearly, the new SEER2 rating is lower than the now old SEER rating. Why is that? Shouldn’t both be measuring the energy efficiency which doesn’t changes? Is the SEER2 a 2.0 version of the SEER rating?

Let’s clear this thing up in the simplest manner possible:

Seasonal Energy Efficiency Rating (Calculation + Measurement)

SEER stands for Seasonal Energy Efficiency Rating. Similarly, SEER2 stands for Seasonal Energy Efficiency Rating 2. The goal of introducing the SEER rating was to determine the efficiency of an HVAC unit (cooling mode) in real-time conditions.

The premise for SEER rating (SEER2 has the same premise) is that an HVAC unit runs:

  • At 100% load 1% of the time. This is referred to as the 100% Energy Efficiency Rating or EER100%.
  • At 75% load 42% of the time. This is the EER75%.
  • At 50% load 45% of the time. This is the EER50%.
  • At 25% load 12% of the time. This is the EER25%.

The difference between SEER and SEER2 rating is not the calculation. The math here is the same. The difference is in measuring these partial and full energy efficiency ratings (EER100%, EER75%, EER50%, EER25%).

Namely, the US Department of Energy figured out that the test conditions at which we measure these EER ratings for SEER rating calculation are a bit off. They figured out that the external pressure when measuring EER ratings was too high and didn’t reflect real-time conditions as closely as possible.

To fix this, the DOE has introduced this new SEER2 rating. Here is the only difference between SEER and SEER2 ratings:

  • SEER measurements are made at 0.1 inches of water column external pressure.
  • SEER2 measurements are made at 0.5 inches of water column external pressure.

As we can see, in the new SEER2 rating, the external pressure – the pressure an HVAC unit works against – is 5 times higher (0.5 in. WC) than for the SEER rating (0.1 in. WC). In the document, it is also apparent that DOE considered 0.3 in. WC for SEER2 rating as well, but decided to go with 0.5 in. WC.

Now, this may seem like change is just one test condition, but it does have considerable implications. Namely, the measured EER ratings at 25%, 50%, 75%, and 100% load are now lower. Consequently, the calculated SEER2 rating is thus lower than the SEER rating.

Let’s look at how SEER and SEER2 ratings compare:

SEER Vs SEER2 Comparison

Prior to 2023, we were comparing 14 SEER vs 15 SEER, 14 SEER vs 16 SEER, 16 SEER vs 20 SEER ratings, and so on. The introduction of the SEER2 rating made these comparisons a bit more complex.

Here is the numerical comparison of the SEER vs SEER2 rating from the original 2016 document:

SEER Rating: SEER2 Rating: Percentage Difference:
14 SEER 13.4 SEER2 SEER2 is 4.3% lower than SEER
14.5 SEER 13.8 SEER2 SEER2 is 4.8% lower than SEER
15 SEER 14.3 SEER2 SEER2 is 4.7% lower than SEER

We can clearly see that the SEER2 rating is (numerically) about 4.5% lower than the SEER rating. You can check the full SEER to SEER2 conversion from 12 SEER to 30 SEER here.

Example: When comparing two different heat pumps or air conditioners, we now have to compare 13.4 SEER2 vs 14.3 SEER2 instead of 14 SEER vs 15 SEER.

In short, the SEER and SEER2 measure the seasonal energy efficiency of heat pumps or AC units. The new SEER2 will give us a more realistic efficiency, but it will take some time for us to get used to comparing SEER2 ratings instead of familiar SEER ratings.

2 thoughts on “SEER Vs SEER2 Rating: What’s The Difference? (+ Implications)”

    • Hi Paul, thanks for the heads up. You are correct, we made a mistake, and fixed it now. SEER2 is measured at 0.5 in. WC and SEER is measured at 0.1 in. WC. Thank you again.


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