Sizing is the decision that determines whether you like your new air conditioner. Get it wrong and no amount of efficiency rating, brand reputation, or smart thermostat will fix the comfort problem.
The rules of thumb below are a starting point for budgeting. The actual specification should always come from a room-by-room Manual J load calculation.
Why Square Footage Alone Fails
Two identical 2,000 square foot homes on the same street can need a full ton of difference in capacity. Here is what changes the answer.
- Orientation — west-facing glass takes brutal afternoon sun load
- Window type — single-pane clear glass versus laminated low-E impact glass
- Ceiling height — vaulted ceilings add volume the tonnage table ignores
- Attic insulation depth and radiant barrier presence
- Roof color and material — a reflective metal roof lowers attic temperature substantially
- Shading from mature trees
- Air infiltration — a tight new build versus a 1970s block home
- Occupancy and appliance load, including kitchens and home offices
The Oversizing Trap
The instinct is to buy bigger for a Florida summer. It is the single most common and most damaging sizing error made here.
An oversized system hits the thermostat setpoint in a short burst and shuts off before the coil has been cold long enough to condense meaningful moisture out of the air. You end up with a house that is 74 degrees and 65 percent relative humidity — cold, damp, and prone to mold.
- Short cycling wears the compressor and shortens system life
- Poor dehumidification creates mold and dust mite conditions
- Larger temperature swings between cycles
- Higher equipment cost for worse comfort
The Undersizing Trap
The opposite error is less common but equally real. An undersized system runs continuously through August, never fully satisfies the thermostat, and drives up both the electric bill and the wear rate.
Some contractors intentionally undersize to win a bid on price. Ask for the load calculation output, not just a tonnage number.
Latent vs Sensible Load
Sensible load is temperature. Latent load is moisture. In Florida, latent load can represent 30 percent or more of the total cooling requirement — far higher than in dry climates.
Equipment is rated for both. A properly specified Florida system prioritizes a strong latent capacity ratio, which usually points toward two-stage or variable-speed equipment that runs longer at lower output.
Ductwork Is Part of the Sizing
A 4-ton system connected to duct designed for 3 tons will never deliver 4 tons of cooling. Return air is the most frequently undersized element in older Florida homes.
A complete replacement quote should include static pressure measurement and any duct modifications needed to support the new equipment. If it does not, you are buying capacity you will never receive.
Rough Tonnage Guide — Florida Climate
| Home Size | Typical Tonnage | BTU Capacity |
|---|---|---|
| 800 – 1,100 sq ft | 2.0 ton | 24,000 BTU |
| 1,100 – 1,400 sq ft | 2.5 ton | 30,000 BTU |
| 1,400 – 1,700 sq ft | 3.0 ton | 36,000 BTU |
| 1,700 – 2,100 sq ft | 3.5 ton | 42,000 BTU |
| 2,100 – 2,500 sq ft | 4.0 ton | 48,000 BTU |
| 2,500 – 3,200 sq ft | 5.0 ton | 60,000 BTU |
Frequently Asked Questions
- What size AC do I need for a 2,000 sq ft house in Florida?
- Most 2,000 square foot Florida homes need about 3.5 to 4 tons, but insulation, window type, ceiling height, and shading can shift that by a full ton. A Manual J load calculation is the only reliable answer.
- Is a bigger AC better?
- No. An oversized system cools the air quickly, shuts off, and never runs long enough to remove humidity. In Florida that produces a cold, clammy house, mold risk, and premature compressor wear from short cycling.
- What is a Manual J calculation?
- Manual J is the industry-standard room-by-room heat load calculation. It accounts for square footage, orientation, insulation, window specs, infiltration, occupancy, and appliance loads to size equipment correctly.
- Does impact glass change my AC sizing?
- Yes. Laminated insulated impact glass sharply reduces solar heat gain, which can lower the required tonnage. If you have upgraded windows, do not simply match your old system's size.
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