Most Florida ACs are 30% too big — and humidity is why.

There isn't one — and that's the whole point. The industry's bad habit is 500 square feet per ton for Florida homes, which almost always oversizes. An airtight 2,000 sqft home with modern double-pane windows and R-38 attic insulation might need 2 tons. A 1960s 2,000 sqft block home with single-pane jalousies and R-11 ceiling insulation might need 3.5 tons. The real number comes from a Manual J load calculation that accounts for every window, wall, ceiling, orientation, infiltration rate, occupancy, and internal-gain source. If a contractor quotes a system size from just the square footage, they're guessing — and in Florida that guess almost always lands too big.

Three reasons, in decreasing order of defensibility. First, genuine climate concern — 95°F design days with 80% humidity are no joke, and an undersized system can't hold setpoint during the worst hour of the worst day. Second, complaint avoidance — a slightly oversized system cools fast and impresses the homeowner on day one; an undersized system that struggles on extreme days generates callbacks. Third, and most commonly, the rule-of-thumb that's handed down through the trade has never been corrected. Most contractors have never run a Manual J; they use 500 sqft/ton and add a half-ton 'for Florida.' The result is a system 30–50% larger than the actual design load.

Three things, all serious in Florida. First, short cycling — an oversized system hits setpoint too fast, shuts off, warms back up in 20 minutes, and cycles again. That rapid cycling wears the compressor faster and drives up the utility bill. Second, poor humidity control — Florida's actual cooling load is roughly 40% latent (dehumidification) and 60% sensible (temperature). A short-cycling oversized system never runs long enough to dehumidify properly, so you get 75°F rooms at 62% RH that feel clammy. Third, comfort complaints — rooms far from the thermostat stay warmer because the system cuts off before air reaches them. The oversized system delivers worse comfort than a right-sized one.

Four signs, any two of which are diagnostic. One: indoor humidity stays above 55% even with the AC running normal cycles — a right-sized system in Florida pulls to 48–52%. Two: cycle times are under 10 minutes on a 90°F afternoon — a right-sized system runs 20–45 minutes at design load. Three: rooms far from the thermostat stay 3–5°F warmer than the thermostat room. Four: you hear the compressor cycling on and off more than 3 times an hour. Any of these individually could be another problem (low refrigerant, leaky ducts, dirty filter) — but two or more together are the oversizing fingerprint.

Manual J (published by ACCA — the Air Conditioning Contractors of America) is the residential HVAC load calculation standard. A full Manual J analysis computes the home's design heat gain — in BTU/hour — broken out by source: solar gain through each window (by orientation, glass type, shading), conductive gain through walls and ceilings (by R-value), infiltration (by measured or estimated air changes per hour), internal gains (occupants, appliances, lights), and ventilation. The output is two numbers: sensible load and latent load, both in BTU/hr. Divide by 12,000 to convert to tons. A 2,500 sqft Florida home typically calculates to 2.5–3 tons under Manual J, not the 4 tons a contractor's rule-of-thumb would specify.

If it's a $150–$300 service, yes — it's the single highest-ROI dollar you'll spend in the replacement process because it affects equipment size and every subsequent cost. A properly sized 2.5-ton system vs a 4-ton system on the same home: roughly $2,000 less in equipment cost, 20% less in electricity over the system's life, and qualitatively better comfort and humidity control. The catch: real Manual J takes 60–90 minutes of contractor time with a laptop and real software (Wrightsoft, Elite RHVAC, CoolCalc). A 'Manual J' that's actually just a sqft calculation entered into software for appearances isn't worth paying for. Ask the contractor to walk you through the inputs.

Yes — and a contractor who only runs Manual J is doing a third of the job. Manual S is the equipment selection step: it takes the Manual J load and finds a specific AHRI-certified equipment match that delivers close to the calculated load without going over. A Manual S match is critical because a 3-ton nameplate system doesn't deliver 3 tons at every condition — it varies by indoor and outdoor temperature. Manual D is the duct design calculation: it sizes each duct run for the correct airflow to each room based on Manual J room-by-room loads. Skipping Manual D is the primary reason a right-sized system still delivers unbalanced comfort. Any quote over $12,000 should include J, S, and D — it's professional standard.

Hugely. In a dry climate like Phoenix, a 3-ton AC removes maybe 5% of its cooling capacity as dehumidification. In Florida, that same 3-ton system spends 30–40% of its runtime on latent load — pulling water out of the air rather than cooling it. Two practical implications. First, Florida-appropriate sizing favors running the equipment closer to continuous at design conditions rather than cycling — which means slightly undersizing a unit on paper can deliver better real-world humidity control. Second, variable-speed (inverter) equipment handles the latent/sensible balance dramatically better than single-stage equipment because it can match its capacity to the actual load instead of cycling off.

Yes — CoolCalc.com offers a free homeowner-accessible ACCA-approved Manual J tool, and the Department of Energy's BEopt and EnergyGauge are professional-grade calculators that a technically-minded homeowner can run. The inputs require some measurement: window areas by orientation, wall R-values (or construction age proxy), attic R-value, square footage by room, typical occupancy. You'll come out with a BTU/hr load that you can compare against what a contractor is quoting. If your DIY Manual J says 2.5 tons and a contractor is quoting 4 tons, that's a conversation worth having — and a reason to get a second quote.

We don't default — we calculate. Every quote runs a full Manual J from the public property record (square footage, construction year, window count from the tax assessor's record) plus photo confirmation of roof orientation and window types. For atypical homes — additions, high ceilings, glass walls, unusual occupancy — we flag the configuration during the assessment and request the additional inputs needed for accurate sizing. The result: our tier cards show the right size for your specific home, not a one-size-fits-all default. This is a material part of why our effective cost beats the typical 'here's a 4-ton system' quote on the same house.