AC Running Nonstop but Your Florida House Feels Humid? The Oversizing Problem

The thermostat reads 75. The AC has been running since breakfast — or worse, kicking on and off in short bursts — and the house still feels like a damp towel. In Florida, this specific misery usually is not broken equipment. It is a system doing exactly what it was sized to do, and sized wrong.

Florida cooling is two jobs, not one

An air conditioner in Florida has to do two things: drop the temperature (the sensible load) and wring moisture out of the air (the latent load). Florida racks up 3,409 cooling degree days a year against just 566 heating degree days, so cooling is essentially the whole job — and humidity is the defining engineering constraint. Latent load is as important as temperature here, which is why proper sizing and dehumidification matter more than raw efficiency numbers.

Temperature drops fast. Moisture removal is slow. Dehumidification only happens while the indoor coil is cold and air is moving across it for a sustained stretch — condensation takes runtime.

The oversizing trap

Here is the failure mode: an oversized system reaches the thermostat setpoint too fast to dehumidify. It blasts the air down to 75 in a few minutes, satisfies the thermostat, and shuts off — before it has pulled meaningful moisture out of the air. Then it does it again. And again. That is short-cycling, and the result is a house that hits its target temperature and still feels clammy.

The human response makes it worse. The house feels sticky, so you lower the setpoint. Now the air is colder, but cold-and-damp still feels clammy — just at a lower temperature, with a higher electric bill.

If a contractor suggests going up a size “to be safe,” understand what you are buying: in a humid climate, extra capacity is not headroom. It is the reason your house will feel like a basement.

Bigger also costs more up front

Oversizing is not just a comfort mistake; you pay extra for it. Typical installed replacement ranges:

• 2 tons: $4,000-$8,500
• 2.5 tons: $4,500-$9,500
• 3 tons: $5,000-$11,000
• 3.5 tons: $5,500-$12,000
• 4 tons: $6,000-$13,500
• 5 tons: $7,000-$15,000

Jumping from a correct 3-ton to an unnecessary 4-ton adds roughly a thousand dollars at the bottom of the range and $2,500 at the top — for worse comfort. And a high SEER2 rating does not rescue a wrong-size unit: 16-17 SEER2 equipment carries about a 15% price premium and 18+ SEER2 about 35% over code-minimum 14.3 SEER2, but efficiency tiers do nothing about latent load if the unit never runs long enough to dehumidify.

Rule out the cheap problems first

Before concluding your system is oversized, spend $75-$200 on a diagnostic. Several cheaper culprits produce humid-house symptoms:

• Low refrigerant. A leaking system loses both capacity and dehumidification. Leak detection and repair runs $200-$1,500.
• Clogged condensate drain. All the moisture your coil removes leaves through the drain line, and Florida humidity keeps drain lines busy. Clearing runs $75-$250.
• Leaky ducts. The Florida Solar Energy Center studied this in Florida homes and found return leaks averaging 10% of air handler flow — humid attic and garage air pulled straight into your system. Duct repair cut air-conditioning energy use by 18%, at an average cost of $200 per home in 1990 dollars (roughly $490 today), with a simple payback under two years. If your ducts are pulling in outside moisture, no condenser size fixes that.

What to ask a contractor

When you do replace, the single most important question is: will you perform a load calculation on my house? Ask for Manual J by name. A real load calculation works room by room from your actual windows, insulation, orientation, and air leakage — not from square footage, and not from whatever tonnage the old unit happened to be. Matching the old unit assumes the original installer sized it correctly, and the clammy house you are living in is evidence against that.

Two red flags: a tonnage quoted over the phone before anyone has seen the house, and any version of “we will just put in the same size.” Also ask directly how the proposed system will handle latent load — a contractor who can talk fluently about humidity in a Florida install is the one you want.

Where this meets repair-versus-replace

If your system is mechanically healthy and merely oversized, replacement is an expensive comfort fix — weigh it against the unit’s age. But if an oversized unit is also facing a major repair — a compressor out of warranty runs $1,200-$2,800, an evaporator coil out of warranty $650-$2,500 — replacement solves two problems with one check, and this time you get to size it correctly.

Remember that a changeout requires a mechanical permit everywhere in Florida, with fees typically $75-$400 depending on jurisdiction (approximate; set locally). And the rebates point in the right direction: FPL pays $200 instant at SEER2 15.2 or higher, TECO pays $40 at SEER2 15.2 or $550 at 16.2, JEA pays $200, and OUC pays $45-$1,150 by tonnage and SEER2 tier — all rewards for choosing efficient equipment, correctly sized, rather than simply more of it.

Right-sized beats supersized in Florida, every time. The load calculation is how you get there.