What size AC do I need for my Florida home?

You're shopping for a new AC. The first contractor walks through your home for ten minutes and announces "you need a 4-ton." The second contractor measures rooms and says "definitely a 4-ton." The third contractor doesn't measure at all and says "5-ton, definitely 5-ton." Who's right?

Probably none of them. Sizing an AC for a Florida home properly is more involved than any of those approaches, and the consequences of getting it wrong are expensive in three different ways: higher install cost (wasted capacity), worse comfort (humidity problems), and shorter equipment life (short-cycling).

This post explains how AC sizing actually works, why the rules of thumb you'll find online get it wrong for Florida homes specifically, and what to ask any contractor who's quoting you a system.

The "1 ton per 600 sq ft" myth

If you Google "what size AC do I need," you'll find dozens of articles offering a square-footage rule of thumb. The most common version: 1 ton of cooling per 600 square feet in Florida.

That rule of thumb works about as often as a stopped clock tells the right time, occasionally, by accident. Here's what it ignores:

• Ceiling height. A 2,000 sq ft home with 8' ceilings has 16,000 cubic feet of air to cool. A 2,000 sq ft home with 12' ceilings has 24,000. The rule of thumb gives both the same AC.
• Insulation R-value. A new home with R-30 attic insulation needs roughly 30% less cooling than the same home with R-13.
• Window area and orientation. South- and west-facing glass adds enormous cooling load. A wall of windows facing west in a Florida home can require 0.5-1 ton of dedicated capacity by itself.
• Air infiltration. Older homes with single-pane windows and unsealed doors leak air constantly. Newer tightly-built homes don't.
• Occupancy. Each person in the home adds about 250 BTU/hour of heat load.
• Heat-generating equipment. Big TVs, gaming PCs, kitchens with gas stoves, sunrooms with Florida tile, all add load.
• Ductwork. Leaky or undersized ducts can lose 20-30% of the AC's capacity before air reaches the rooms.

Two homes that are both 2,000 sq ft can need ACs that differ by an entire ton. The square-footage rule of thumb has no way to account for that.

What proper sizing actually involves

The correct way to size a residential AC is a Manual J load calculation, that's the industry standard developed by ACCA (Air Conditioning Contractors of America), and it accounts for all the variables above. A proper Manual J takes about 60-90 minutes on-site, room by room, plus another 30 minutes back at the office to compile the results.

The output is a specific BTU requirement for your home (something like "this home needs 33,400 BTU/hr at design conditions"). That number tells us exactly which AC size matches your home. Anything more, anything less, and you're sized wrong.

Most Florida HVAC contractors don't do Manual J calcs because they take time and the math is real. They eyeball it. They use the "rule of thumb." They match what the previous unit was. Sometimes they upsize "just to be safe," which is the opposite of safe in Florida humidity.

Why oversizing is the worst mistake in Florida specifically

You'd think a too-big AC would just cool too well, who cares? In Florida, oversizing creates a specific, painful problem: your home gets cold without getting comfortable.

Here's why. AC does two jobs simultaneously: it cools the air, and it removes humidity. Cooling happens fast. Dehumidification requires the system to run for extended periods, the longer it runs, the more water condenses on the indoor coil and drains away. Long, slow run cycles are how Florida homes get below 50% relative humidity, where they actually feel comfortable.

An oversized AC drops the air temperature to the thermostat setpoint quickly, then shuts off. It hasn't run long enough to pull water out of the air. So you end up with the house at 72° but 60% humidity, which feels clammy and gross. Most Floridians are familiar with this feeling: they crank the thermostat down to 68° trying to "feel cooler," but the real problem is humidity, and lower thermostat setpoints just make it worse (and triple the FPL bill).

The shorter answer: a properly-sized AC running longer cycles will keep your home more comfortable at 76° than an oversized AC at 72°. And it'll cost you less to run.

What about ductwork?

Even a perfectly-sized AC won't perform if the duct system can't deliver the air properly. Common Florida duct problems:

• Undersized return ducts. Common in older Palm Beach homes. The system can't pull enough air across the coil, leading to freeze-ups and short-cycling.
• Leaky ducts in the attic. Florida attics get to 130°+ in summer. Leaky ducts are pumping cold air into a hot attic, you're paying to cool the attic.
• Poor airflow balancing. Some rooms get all the cold air; others none.

A proper install includes a duct static pressure test as part of the load calculation. If the ducts can't handle the new equipment, the contractor should tell you that upfront, and either include duct modifications in the quote or recommend a smaller system.

Florida-specific sizing rules of thumb (the better version)

If you absolutely want a quick estimate before a contractor visits, here's a more honest version of the rule of thumb for typical Florida homes:

• 1,000-1,500 sq ft: usually 2 to 2.5 tons
• 1,500-2,000 sq ft: usually 2.5 to 3 tons
• 2,000-2,500 sq ft: usually 3 to 3.5 tons
• 2,500-3,000 sq ft: usually 3.5 to 4 tons
• 3,000-4,000 sq ft: usually 4 to 5 tons (often split into 2 systems)
• 4,000+ sq ft: nearly always 2 separate systems, sized individually

Important caveat: these are starting points only. A 1,800 sq ft home with vaulted ceilings, a wall of west-facing windows, and old single-pane glass might need 3.5 tons. A tightly-built 2,200 sq ft home with high-R insulation and good shading might need only 2.5. The right answer is the load calculation, not the rule of thumb.

What to do next

If you're shopping for a new AC, three things to insist on from any contractor:

1. An on-site visit before the quote. A real load calculation requires walking the home, measuring rooms, looking at insulation. Quotes-by-phone are guesses.
2. A Manual J calculation, in writing. Ask for the load calc report. Reputable contractors will hand you a copy.
3. Honest discussion of duct condition. If your existing ducts are part of the problem, you need to know that before the install, not after.

We do all three on every install. Free on-site quote, written Manual J calc, written duct assessment, and a fixed quote within 48 hours. (561) 503-3003 or request a quote. Palm Beach, Martin, and Broward Counties.