What size HVAC do I need?
Published April 14, 2026 · 6 min read
For a typical well-insulated Florida home, expect roughly 1 ton per 600–700 sqft. Older, leaky, or heavily-shaded homes might land closer to 1 ton per 500 sqft. Modern, tight builds often need 1 ton per 800 sqft. The only way to know precisely is a Manual J load calculation.
Why the old “500 sqft per ton” rule is wrong
Florida HVAC contractors have been quoting “one ton per 500 square feet” for decades. It's simple, it's fast, and it's the reason half the homes in the state are clammy. The rule was born in the 1970s, when homes were leaky, insulation was thin, and windows were single-pane. It drastically oversizes modern homes built or retrofitted with any energy-efficiency upgrades.
An oversized system cycles on, blasts cold air for 6 minutes, hits the thermostat setpoint, and shuts off. Six minutes isn't enough time to pull meaningful humidity out of the air, so your house ends up cold and damp. You then turn the thermostat down to 68°F to compensate, which runs up your electric bill and makes the problem worse.
What Manual J actually calculates
Manual J is the industry-standard load calculation from the Air Conditioning Contractors of America (ACCA). It accounts for:
- Square footage and ceiling height (volume, not just area)
- Insulation R-values in walls, attic, and floor
- Window area, orientation, and glazing type (single/double/low-E)
- Air infiltration rate (tight vs leaky envelope)
- Number of occupants and typical internal heat loads
- Shade from trees, overhangs, and neighboring buildings
- Climate zone design temperatures (99% cooling dry-bulb)
The output is a BTU/hour load in 12,000-BTU increments (= 1 ton). A properly-done Manual J usually lands your sizing within ±0.25 ton. Anything more imprecise than that is a rule of thumb, not a calculation.
Typical Florida sizing by home type
| Home profile | Sqft per ton | 2000 sqft = ? tons |
|---|---|---|
| 1980s block home, original windows | 500 | 4.0 tons |
| 1990s/2000s home, updated windows | 600 | 3.5 tons |
| 2010s-era new build | 700 | 3.0 tons |
| 2020+ tight build, spray-foam | 800 | 2.5 tons |
These are starting points, not answers. A two-story home with a west-facing wall of windows needs more tonnage than a ranch-style home with the same sqft. A Manual J is the only way to know for sure.
How AIRA sizes your system
When you run our assessment, AIRA pulls your property from public records (year built, square footage, stories), asks about insulation upgrades and window replacements, maps the orientation of your main windows, and runs a real Manual J using ACCA's 8th-edition tables. The result is usually half a ton smaller than what a walk-in contractor would quote — which sounds like bad news until you realize that's exactly the difference between a clammy house and a comfortable one.
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Get a real sizing in 5 minutes
Manual J-level accuracy, explained in plain English.