Part of our guide to Repair or Replace? How to Decide on an Ageing Air Conditioner
The number on the sticker is real and it is routinely oversold. It measures something specific, and whether paying more for a bigger one makes sense depends almost entirely on where you live.
SEER2 is cooling efficiency across a season — output divided by electricity used. Minimums are set by region and are higher in the south, where cooling runs longer. Going above the minimum pays back only where you run the system many hours a year; in a short cooling season the premium frequently never returns. And SEER says nothing about heating.
What the number means
SEER is a ratio: cooling delivered over a season, divided by the electricity consumed to deliver it. A higher number means more cooling per unit of electricity.
The important thing is that the savings are not linear. Going from a low rating to a moderate one is a much larger proportional improvement than going from a high one to a higher one, because you are dividing by a bigger number each time. The jump from 14 to 16 saves considerably more than the jump from 20 to 22.
That is the arithmetic the upsell tends to skip.
SEER2, and why old numbers do not compare
Since 2023 the US rates equipment as SEER2, tested under higher external static pressure to better represent a real ducted system rather than a laboratory bench.
The consequence catches people out: the same physical unit scores lower under SEER2 than under old SEER. A number that looks like a downgrade next to a decade-old system may be the same or better equipment measured more honestly.
So when comparing against an old unit's rating, or an old article, check which metric is being quoted. They are not interchangeable.
Minimums depend on where you live
The US sets regional minimum efficiency standards. Southern and southwestern states carry higher minimums than northern states, because the cooling season is longer and the energy at stake is greater.
Two practical consequences:
- Your installer must meet your region's minimum, so the floor is not negotiable
- Equipment legal to install in a northern state may not be legal in a southern one
Whether a higher rating repays its premium is arithmetic with three inputs, and you have all three:
1. The price difference between the two units, from your quotes. 2. Your electricity rate, from your bill. 3. Roughly how many hours a year you actually cool.
The third is what decides it. In a climate that runs air conditioning most of the year, a high-efficiency unit can repay the premium comfortably within its lifespan. In a climate with a six-week cooling season, the same premium may outlast the equipment. Nobody can give you a national answer to this, and any article that quotes one is guessing on your behalf.
What matters more than the sticker
Correct sizing. An oversized system short-cycles: it cools the air quickly, shuts off before removing humidity, and leaves the house cold and clammy while wearing itself out. Sizing should come from a load calculation of your actual house — not square footage, not the size of the old unit.
Duct condition. Leaky or undersized ducts waste conditioned air into attics and crawlspaces. A high-efficiency unit on bad ducts underperforms an ordinary unit on good ones. This is also precisely what SEER2's testing change was designed to capture.
Installation quality. Refrigerant charge, airflow setup and commissioning affect delivered efficiency substantially. The rating is what the equipment can do; installation decides what it does.
Single-stage versus variable-speed. Variable-speed equipment runs longer at lower output, which dehumidifies better and holds temperature more steadily. For comfort, that often matters more than the headline number.
What to actually do
- Find your region's minimum — that is your floor
- Get quotes at the minimum and one step above, from the same installer
- Run the three-input calculation with your own rate and cooling hours
- Check for utility rebates, which frequently target higher-efficiency equipment and can change the answer
- Spend leftover budget on ducts and sizing before spending it on a bigger number
If you are also weighing what type of system to install, see heat pump vs central air. If you are deciding whether to replace at all, see repair or replace.
This is general information, not professional advice — see our disclaimer.
Frequently asked questions
What does SEER measure?
Seasonal cooling efficiency — cooling delivered across a season divided by electricity consumed. Higher is more efficient, and the scale is not linear in savings.
What changed with SEER2?
From 2023 the US switched to SEER2, tested against higher external static pressure to better reflect real ducted installations. The same unit scores lower under SEER2 than under old SEER, so the numbers are not comparable.
What is the minimum I can buy?
It depends on your region — the US sets different minimums for northern and southern states, with the south higher because cooling hours are longer. Your installer must meet your region's minimum.
Is a higher SEER always worth it?
No. The saving depends on how many hours you cool, your electricity rate, and the price gap between units. In a short cooling season the premium often never repays itself.
Does SEER affect heating?
No. SEER covers cooling only. Heat pump heating efficiency is rated by HSPF2, and a unit can be strong on one and ordinary on the other.
Sources
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