SEER And EER Rate The Same Machine On Different Days

Cooling equipment sold in the United States carries more than one efficiency figure, and they are not competing claims about the same thing. They describe different operating conditions.

One is a season and one is a moment

The steady-state rating expresses cooling delivered per unit of electrical input at a single specified outdoor condition, with the equipment running continuously.

The seasonal rating is a weighted calculation across a modeled cooling season, including a range of outdoor temperatures and the losses from cycling on and off.

Both are legitimate. They answer different questions, which is why a machine can look better on one and worse on the other than a competitor.

The seasonal figure contains a climate assumption

A seasonal rating weights performance by how many hours are expected at each outdoor temperature, using a modeled climate rather than yours.

In a place where the cooling season is long and hot, the hours near the design condition dominate, and steady-state performance at high outdoor temperature matters more.

In a mild climate with intermittent cooling, cycling losses and part-load behavior dominate, which is what the seasonal number captures well.

Variable capacity changes which figure applies

Single-stage equipment is either on at full capacity or off, so its part-load efficiency is dominated by starting and stopping.

Variable-speed equipment can run continuously at reduced output, matching the load rather than cycling, and it performs best at part load rather than at full.

Seasonal ratings reward this and steady-state ratings do not, which is why the gap between a machine's two numbers hints at how it modulates.

Installation moves the delivered efficiency

Ratings are established on matched equipment tested as a system. Field installations frequently pair components that were not tested together.

Duct leakage, refrigerant charge and airflow setup all move actual performance away from the rating, generally downward and sometimes substantially.

An efficiently rated system installed carelessly can consume more than a modest system installed properly, and no label captures that.

The ratings and the test methods change

Test procedures behind these figures have been revised over the years, including changes to the external static pressure the equipment is tested against.

That means ratings from different eras are not directly comparable, and a lower number under a newer procedure may describe the same machine as a higher one under an older test.

Comparing equipment therefore requires establishing which test version produced each figure, which is stated in the documentation rather than in the advertising.