Homeowner wants me to just replace his 3-ton with a 4-ton because 'bigger is better' in Florida.

Stop. Don't install a 4-ton without a load calculation.

Why it matters: Oversizing causes short-cycling, poor humidity control, higher energy bills, and premature equipment failure. In Florida's humid climate, proper dehumidification is critical—oversized units can't run long enough to remove moisture, leading to mold and discomfort.

Code requirement: Per ACCA Manual J (required by Florida Building Code, Section M1601.3), you must perform a load calculation before equipment replacement. Installing without one violates code and voids warranties.

Key Manual J inputs that drive sizing:

• Orientation & solar exposure (windows, overhangs, shading)
• Insulation levels (attic, walls, floors)
• Air leakage (infiltration rates)
• Internal gains (occupancy, appliances, lighting)
• Design temperatures (outdoor 95°F/78°F wet bulb, indoor 75°F/50% RH)
• Ductwork location (attic ducts add significant load)

What to tell the homeowner: "I understand you want maximum cooling, but a 4-ton unit will actually make your home less comfortable and cost more to run. Let me perform a proper Manual J load calculation using your home's specific characteristics—insulation, windows, orientation, and occupancy. This ensures we size the system correctly for optimal comfort and efficiency. It's also required by Florida code."

Bottom line: Do the load calc. It protects you legally and gives the homeowner the right system for their actual needs.

Don't do it. Oversizing in Florida creates comfort, health, and durability disasters. You need a Manual J load calculation (ACCA Standard, required by FBC Energy Conservation §R403.7 / IRC §M1401.3).

Why 4-ton fails in FL:

1. Short-cycling: Satisfies thermostat in 5–7 mins. Coil never gets cold enough to wring out humidity → mold growth, clammy 75°F.
2. Duct destruction: Existing ducts sized for 1200 CFM (3-ton). 4-ton needs 1600 CFM. Static pressure spikes → noise, coil freeze, blower motor death, leaked conditioned air into attic.
3. Short equipment life: Compressor starts 3–4x more often.

Manual J Inputs That Actually Drive the Number (get these wrong = garbage output):

• Orientation & Shade: Exact window azimuth, overhang depth, trees, neighbor buildings. West-facing glass in FL is the #1 load driver.
• Envelope Reality: Measured window U-value/SHGC (not "double pane"), actual wall/ceiling R-value (pull insulation back), blower door test (ACH50). Guessing "tight" vs "leaky" swings load 15–25%.
• Internal Gains: Real occupancy, appliance schedules, duct leakage location & volume (Manual D), ventilation rate (ERV/HRV vs exhaust only).
• Design Temps: FBC Table R301.2(1) – Use 99%/1% outdoor design temps for the specific city (e.g., Miami 92°F/47°F vs Tallahassee 94°F/28°F), not "Florida average."

Your move: "I'll run the Manual J (required for permit). If it confirms 3-ton, we fix ducts/airflow. If it says 3.5, we do 3.5 with variable capacity. I won't install a 4-ton on guesswork – it violates code and my license."