Picking the right size air conditioner is the single most important decision in a Florida AC replacement, and it is the one homeowners most often get wrong. AC capacity is measured in tons, where one ton equals 12,000 BTU per hour of cooling. The common rule of thumb is one ton for every 400 to 500 square feet of conditioned space, but in coastal Brevard County that rule is only a starting point. Year-round heat, daily humidity, and salt-laden air change the math, and a unit that is even half a ton too big can leave your home cool but clammy.
The reason bigger is not better comes down to how AC removes moisture. A correctly sized system runs in longer, steadier cycles that pull humidity out of the air the whole time it runs. An oversized unit blasts the thermostat down fast, shuts off, and never runs long enough to dehumidify, so the house feels cold and damp at the same time. In a humid climate like Melbourne and the rest of Brevard, that is the most common comfort complaint we are called out to fix, and it almost always traces back to a system that was sized by square footage alone. This guide shows the tonnage ranges by home size, the factors a proper load calculation adds, and why a Manual J is worth insisting on.
Start with the square-footage rule, then adjust
As a first estimate, divide your conditioned square footage by 400 to 500. A 1,200 square foot home lands around 2.5 to 3 tons, a 1,600 square foot home around 3 to 3.5 tons, a 2,000 square foot home around 4 to 5 tons, and a 2,400 square foot home around 5 tons. Florida sits at the higher-capacity end of that range because of the cooling load, so we generally use 400 to 450 square feet per ton here rather than the 600 figure used in cooler states.
Why Florida humidity changes the sizing math
Sizing is not only about lowering temperature, it is about removing moisture. Brevard's humidity means the system has to do heavy latent cooling, not just sensible cooling. A unit sized purely on temperature can be too large for the dehumidification job, which is why right-sizing in Florida leans toward longer run times and steady cycling rather than maximum tonnage.
Why an oversized AC is a real problem
An oversized system short-cycles: it cools the air fast, satisfies the thermostat, and shuts off before it has wrung the humidity out. The result is a cold, clammy house, higher electric bills from frequent starts, more wear on the compressor, and a shorter equipment life. Oversizing is one of the most common and most expensive AC mistakes in Brevard County homes.
Why an undersized AC is also a problem
An undersized unit runs constantly, never quite reaches the set temperature on the hottest Brevard afternoons, and drives the electric bill up while it loses the battle. It also wears out early from running nonstop. The goal is the right size, not the biggest size, and not a unit chosen to save a few hundred dollars up front.
The Manual J load calculation is the real answer
A proper sizing uses an ACCA Manual J load calculation, the industry standard. It accounts for square footage, ceiling height, insulation levels, window area and orientation, sun exposure, air leakage, occupancy, and your local Brevard climate data. Synergie AC Repair & Installation runs a load calculation before quoting a replacement, so the tonnage matches your actual home and not a generic chart.
SEER2 and brand do not change the tonnage you need
Efficiency rating and brand are separate from sizing. You still need the correct tonnage whether you choose a Daikin, Goodman, York, Lennox, or Mitsubishi system, and whether it is a 15 or an 18 SEER2 unit. For zoned homes, additions, or rooms the central system struggles to reach, a Mitsubishi or Daikin ductless mini-split is sized per zone instead of for the whole house.
- Conditioned square footage: the starting point, divided by roughly 400 to 450 square feet per ton in Florida's climate.
- Ceiling height: vaulted or high ceilings add cooling volume that a flat square-footage figure misses.
- Insulation and air sealing: a tight, well-insulated Brevard home needs less tonnage than a leaky one of the same size.
- Window area and orientation: large or west- and south-facing glass adds solar heat gain and pushes tonnage up.
- Sun exposure and shade: an unshaded coastal home carries a higher load than one shaded by mature trees.
- Humidity and latent load: Brevard's moisture means the system is sized to dehumidify, not just to lower temperature.
- Occupancy and use: more people, kitchens, and heat-producing equipment raise the required capacity.