Buyer's guide

How to choose a central air conditioner

The number that ends most AC regret isn't on the SEER2 sticker — it's the tonnage. Here's what actually separates a good install from a clammy one.

The single biggest mistake, and it isn't the brand

Read enough owner threads about central air and one problem shows up more than any other: the house never quite dehumidifies, the thermostat is set to 78°F just to keep the unit from running constantly, and the air feels cold and clammy at the same time. That isn't a refrigerant problem or a bad compressor. It's almost always an oversized unit.

An air conditioner that's too big for the house satisfies the thermostat fast and shuts off — which sounds like a good thing until you understand that dehumidification only happens while the unit is running. Air has to pass over a cold coil again and again to wring the moisture out of it. A short, powerful cycle cools the air quickly and stops before it has done that work. One building-science consultant who writes about exactly this problem put a number on it after replacing his own AC: he'd sized correctly at 1.5 tons on paper, and still "chickened out and put in a 2 ton unit instead" — his own words, describing the exact impulse that oversizes most systems in America. If a professional who knows better second-guesses his own math, you can guess how it goes for everyone else.

So before you look at a single spec sheet: ask the contractor whether they're sizing from a Manual J load calculation, or matching whatever tonnage is already on the house. "We always put a 3-ton on a house this size" is not an answer. It's a shortcut that produces exactly the short-cycling, clammy-house outcome the owner threads are full of.

SEER2 tells you the average day. EER2 tells you the day you'll actually notice.

SEER2 is the number every retailer prints in bold, and it's a real, useful figure — it's the mandatory federal efficiency rating, and every unit sold in the US has to clear a regional minimum (13.4 in most of the country, 14.3 in the Southeast). But SEER2 is a seasonal average, weighted across a lot of mild days. It's measured, in part, around 82°F outdoor.

EER2 is a different number: efficiency at a single, hard operating point — 95°F outdoor. That's the day your AC actually has to earn its keep. DOE cares about this distinction enough to require it: in Arizona, Nevada, New Mexico and California, federal rules layer an additional EER2 minimum on top of the SEER2 floor, specifically because — in DOE's own words — those climates "experience more high-temperature days requiring air conditioners to work harder."

If you live somewhere with a real, sustained summer — not just a handful of hot days but weeks of it — look at EER2, not just SEER2. Plenty of manufacturers don't even publish it clearly, which itself tells you something about how many buyers know to ask.

The "ENERGY STAR" advice you'll read online is now wrong

Here's a live one: EPA discontinued the ENERGY STAR certification program for central air conditioners on February 1, 2026. If you're reading an article — including older versions of guides on this exact topic — that tells you to "look for the ENERGY STAR label" on a central AC, that advice is stale. There is no such label being issued anymore for this category. EPA's own stated reason was that continuing to badge cooling-only equipment risked undercutting its parallel push toward heat pumps, which both heat and cool.

What to do instead: skip the label entirely and look at the actual SEER2/EER2 numbers, which is what the label was only ever a proxy for anyway — the old ENERGY STAR bar was roughly 13% above the federal minimum, nothing more exotic than that.

Before choosing equipment, settle the indoor-unit electrical question

An air handler is not automatically a 240-volt appliance. Some current full-size air handlers are sold in both 115-volt and 208/240-volt versions. Rheem's RH2TZ technical data, for example, lists 115-volt blower-only models through 60,000 BTU/h (nominal 5-ton airflow) on a 15-amp circuit, as well as 208/240-volt versions of the same sizes. So an existing 120-volt circuit does not, by itself, force an electrical upgrade.

But that is not the same as saying a nearby receptacle is adequate. The exact air-handler nameplate and installation instructions control: ask for its voltage, minimum circuit ampacity (MCA), maximum overcurrent protection (MOCP), and whether the manufacturer requires a dedicated circuit and service disconnect. Have the contractor identify the existing breaker and wire, not merely confirm that the old unit's plug fits.

The important fork is auxiliary electric heat. Rheem's 115-volt RH2TZ variants are blower-only; its electric heat kits are 208/240-volt. A cooling-only installation can therefore be a legitimate 115-volt job, while an air handler with resistance backup heat normally turns into a new 240-volt circuit and panel-capacity question. Do not pay to upgrade the circuit in the abstract, and do not constrain the whole equipment choice merely to preserve an old receptacle. Put both versions on the quote and compare the complete installed systems.

One more compatibility trap: Rheem and Ruud share a corporate parent, but a familiar badge is not proof that an indoor and outdoor unit are a rated pair. Require the AHRI reference number for the exact condenser, coil/air handler, metering device and furnace or heat-kit combination.

Two-stage and variable-speed compressors: comfort first, payback second

A single-stage compressor is on or off — full blast or nothing. If the load calc is slightly off, or the house's needs change with the seasons, a single-stage unit has no way to adjust. It just short-cycles harder.

A two-stage or variable-speed (inverter) compressor can throttle down and run longer at partial output. That's a direct countermeasure to the oversizing problem above — a unit that can back off to 40% capacity on a mild day behaves, in practice, like a smaller and better-matched system even when the tonnage on paper is identical. It's also quieter and produces steadier indoor temperatures, but the dehumidification benefit is the one worth paying for. EPA makes the same narrower claim: variable-capacity equipment can compensate better for some oversizing; it does not make a load calculation optional.

Whether it is worth the price is house-specific. Treat the inverter premium as a comfort, humidity and noise purchase first. Count energy savings only from the AHRI-rated matched systems actually quoted, using local electricity prices and realistic cooling hours. In a hot-humid climate, a house with temperature swings, or a system that must cover a wide load range, the comfort case can be strong. In a mild/dry climate or a house with a tightly sized single- or two-stage alternative, energy savings alone may not repay a large premium.

Do not accept “variable speed” as the whole specification. Ask for minimum and maximum cooling capacity (or turndown ratio), SEER2 and EER2 for the exact matched pair, the parts warranty on the inverter/control boards, surge-protection requirements, and whether the installing company can commission and diagnose that communicating system. A good two-stage quote can be the sane middle option when the inverter premium is high or local service support is thin.

This matters especially when replacing a nominal 5-ton system in a roughly 2,300-square-foot house. That size may be justified by climate, glass, leakage, insulation and duct losses, but square footage alone cannot prove it. Twenty-one years of satisfactory operation does not prove the old tonnage was right either. Before deciding whether an inverter can “fix” that size, require a room-by-room Manual J and the contractor's Manual S equipment selection. A correctly downsized system can be a bigger improvement than changing compressor technology.

The refrigerant question nobody on the review sites asks

As of 2025, new central air equipment has to use a refrigerant with a global warming potential under 700 — which rules out R-410A, the refrigerant that's dominated the market for two decades. Its replacements, R-454B and R-32, are mildly flammable (classified A2L under industry safety standards), which is a genuinely new consideration for a residential comfort appliance.

Two things follow from this:

If you're offered a unit still running R-410A, it's pre-2025 inventory, not new engineering. It's still legal to install — a federal deadline that would have banned installing old R-410A stock was reversed in May 2026 after industry pushback over stranded inventory — but understand the trade: R-410A production is being phased down under the AIM Act, so parts and refill costs for it will keep climbing over the 12-18 years you'll own this thing.

If you're getting an A2L unit (R-454B or R-32, which by now is most new equipment), ask your installer directly whether they're trained and equipped for A2L-specific brazing, charging and leak detection. The exact installer-safety rulebook for these refrigerants was still being finalized by EPA as of this writing — which means "this is what we've always done" is not, this year, a reassuring answer.

We checked sixteen of the highest-ranking pages for "best central air conditioner" — buying guides, brand rankings, model reviews — while researching this category. Exactly one mentioned refrigerant type at all. It's real information almost nobody is giving you.

Warranty: read the shortest number, not the longest one

Manufacturers lead with the compressor warranty because it's usually the longest number on the page — 10, sometimes 12 years. But the compressor isn't the only thing that fails. On an inverter system, the control board is at least as common a point of failure, and boards are covered under the parts warranty, which is frequently shorter than the compressor term.

A "12-year warranty" that's 12 years on the compressor and 5 years on parts is, for practical purposes, a 5-year warranty on the thing most likely to actually need it. Ask for both numbers, not just the one on the box. And ask about the registration deadline — most manufacturers require you to register within 60-90 days of install to get the full term stated on the brochure; miss it and you're quietly downgraded to a much shorter base warranty, and it's the installer's job (not yours) to do it, which is exactly why it gets missed.

What real owners actually report going wrong

Reading a wide sample of trade forums, building-science communities and owner reviews turns up a consistent pattern behind the failures that show up well before a unit's expected life is up: refrigerant leaks from cracking coils, compressors that die at 2-4 years instead of 12-plus, and — separately — installation errors (an incorrect refrigerant charge is a genuinely common one) that get blamed on "a bad unit" when the actual cause is a bad install. One Texas owner's account is representative of how these two causes get tangled together: a technician who charges "off pressure" instead of by weight can produce a system reading nearly 550 PSI against a normal 325-350 range — a mistake with nothing to do with which brand was on the box.

None of this means central air is unreliable. It means the two biggest determinants of whether you're happy with yours in five years are (1) whether it was sized correctly and (2) whether it was commissioned correctly — both contractor decisions, neither one a spec you can shop for.

What to actually ask before you sign anything

• Are you sizing this from a Manual J, or matching what's already there?
• What voltage, MCA and MOCP does the exact indoor unit require; is the existing branch circuit

compliant; and does adding electric heat change the answer?

• What's the AHRI reference number for this exact indoor/outdoor combination?
• What's the EER2, not just the SEER2 — especially if you're somewhere with real summer heat?
• Single-stage, two-stage, or inverter — what are the minimum and maximum capacities, what is

the installed-price premium, and what local-price energy savings justify it?

• What refrigerant, and if it's an A2L (R-454B or R-32), what's your team's training for it?
• What's the parts warranty term, separate from the compressor term — and does it require

registration, and by when?

• Get three quotes. Installed pricing for identical equipment varies more by contractor than

by brand, the same rule that holds for every other system in the house.

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