Coil Swap Check

The Efficiency Number on Your Quote Belongs to a Pair

No manufacturer publishes one efficiency figure for an outdoor unit — they publish a range that depends on the indoor unit it is matched with. And the scale itself changed.

Every quote carries an efficiency number, and it is usually presented as a property of the box going outside. It is not. It is a property of two boxes together, and the manufacturers say so on the same page they print it.

The sheets publish a range, not a figure

Open the standard features table on a Carrier product data sheet and the row is labelled plainly: SEER2 (Range depending on indoor combination).

On the 26SCA5 that range is 14.3 to 17.0 at 1.5 and 2 tons, 14.3 to 16.5 through 3.5 tons, and 13.8 to 15.5 at 4. On the older R-410A 24SCA4 it is 13.4 to 16.0 at the small sizes, falling to 13.4 to 15.0 at 5 tons.

Read the top of those ranges and you have the number that appears in advertising. Read the bottom and you have what the same outdoor unit does on a less favourable pairing. Both are the same unit.

The ceiling moves with capacity, and not in the direction you would guess

On the 24SCA4 the highest figure the family can reach falls as the unit gets bigger: 16.0 at 1.5 through 2.5 tons, 15.5 at 3, 15.2 at 4 and 15.0 at 5. The largest unit in the family has the lowest ceiling in it.

That matters when a system is sized up for comfort. The bigger unit is not simply a bigger version of the smaller one’s rating.

Heating and cooling do not move together

A heat pump carries two ratings and they behave differently. Carrier publishes the 27SCA5 at 14.3 to 16.0 SEER2 in cooling — a spread of nearly two points — against 7.5 to 7.8 HSPF2 in heating, a spread of three tenths.

The indoor unit you choose moves the cooling number substantially and the heating number barely at all.

The scale changed, so old and new numbers are not comparable

This is the one that costs people money in the wrong direction.

Sheets from around 2020 rate equipment in SEER, EER and HSPF. Carrier’s 25VNA4 is published as up to 24 SEER, 15 EER and 13 HSPF, with no “2” on any of them. Sheets from 2022 onward — the 24SCA4’s included, and it is still an R-410A unit — rate the same kind of equipment in SEER2, EER2 and HSPF2.

The second set is measured under a different test procedure and the numbers come out lower for the same machine. So a homeowner reading “24 SEER” off an old sheet and “17 SEER2” off a quote will conclude they are being downgraded, and they may not be. The two figures are not on one scale and cannot be subtracted from each other.

If you want to compare, compare like with like: the SEER2 of what you are being quoted against the SEER2 of an alternative quote.

A certified rating can depend on a part

There is one more layer, and it appears in the accessory notes rather than the headline. Carrier’s 26SCA5 sheet records that some certified combinations of that unit and an indoor unit call for a time-delay relay to reach their published rating — 30 seconds for a MicroChannel indoor unit, 90 for a round tube plate fin one.

The rating on the page assumes the system was built the way it was tested. That is another reason the honest question is not “what SEER2 is this unit” but “which pair is this number from, and is that pair certified”.

What to take from this

The number is real. It just describes a system, not a box — and if the indoor half of that system is your existing coil, which is the situation this whole site is about, then the number on the quote was measured on something else entirely.

The brand rules say whether your coil can stay at all. If it cannot, the pair being quoted is a new pair, and its rating is the one to ask for.

Questions people ask

Is 24 SEER better than 17 SEER2?

You cannot tell from those two numbers, because they are not measured the same way. Sheets printed before about 2022 rate equipment in SEER; current ones rate it in SEER2. A unit whose sheet says 24 SEER and a quote that says 17 SEER2 are being described on two different scales, and putting them side by side tells you nothing.

Why does the same outdoor unit have several efficiency numbers?

Because the rating belongs to the outdoor unit and the indoor unit together. Carrier publishes the 26SCA5 as 14.3 to 17.0 SEER2 at its smaller sizes — a spread of nearly three points, decided by what it is paired with.

What should I ask my installer?

Which indoor unit the quoted figure was taken from, and whether that exact pair is certified. The number is only real for the pair it was measured on.

Sources

This is a starting point, not an approval. Everything here is read from published manufacturer documents and dated, but only the licensed contractor who signs your installation can approve a specific system for your home and your local code. Take the citations on this page to them and ask.