What size AC system do I need in Lake Mary?
It comes from a Manual J load calculation on your house — orientation, glass area, insulation, duct location, infiltration. The median City of Lake Mary home is 2,176 sq ft, but square footage alone will not size a system, and in this market oversizing is the more common and more expensive error.
The Lake Mary variable that breaks rule-of-thumb sizing: the lanai
44.5% of improved residential parcels in the City of Lake Mary tax district have a pool — 2,378 of 5,343, the highest share of the seven Seminole County cities measured from the same appraiser extract. A pool house in this market is usually the house with the wide sliding-glass span onto the lanai, and glass is load. Two houses of identical square footage, one with a 20-foot slider facing west and one without, do not take the same equipment.
Ask for latent load to be broken out from sensible load on the printout. Sensible is temperature; latent is moisture. A system sized on sensible load alone in a humid, pool-heavy market is how you end up with a 74°F house that feels worse than a dry 76°F one. More on pool homes.
If the house has more than one system, each one gets sized separately. That is normal in Heathrow Woods, where homes run 4,147–7,240 sq ft and two or three air handlers is standard.
Square footage is an input, not an answer
The median improved residential parcel in the City of Lake Mary tax district is 2,176 sq ft. The rule of thumb a salesperson can do in their head — roughly 500 to 600 sq ft per ton — would put that house somewhere between three and a half and four and a half tons, which is a range wide enough to be useless and wrong at both ends for particular houses.
A Manual J load calculation takes the inputs that actually vary: orientation, glass area and shading, insulation levels, ceiling height, infiltration, whether the ducts are inside conditioned space or in a 120°F attic, and how many people live there. Two 2,176 sq ft Lake Mary houses on the same street, one facing west with a wall of lanai glass and one facing north under oaks, do not have the same load.
Ask for the printout. “The old one was a three-ton” is not a load calculation — it repeats whatever the last contractor guessed, which may itself have been a repeat of the guess before it.
Where sizing goes wrong in Lake Mary specifically
- Oversizing on pool homes. 44.5% of City of Lake Mary parcels have a pool, and pool homes carry the wide glass span and the high latent load. The instinct is to add capacity; the effect is short cycling and a cold, clammy house. Why that backfires ›
- Sizing one system for a house that needs two. Heathrow Woods homes run 4,147–7,240 sq ft, where two or three air handlers is normal. Each system needs its own calculation, and a single-tonnage quote for such a house is a warning sign.
- Sizing for ducts you are not keeping — or keeping ducts you sized past. A new higher-airflow system on an undersized 1988 return will not deliver its rating.
- Ignoring latent load entirely. If the calculation does not break moisture removal out from temperature, it has not described a Central Florida house.
The question, in the wording people ask it
What Size System Do I Need?
The only honest answer is that it comes from a Manual J load calculation on your house — orientation, glass area, insulation, duct location, infiltration. The median house in the City of Lake Mary tax district is 2,176 sq ft, but square footage alone will not size a system, and copying the tonnage off the old data plate just repeats whatever the last contractor guessed. In this market oversizing is the more common error: a system too large short-cycles and never runs long enough to pull humidity out of the house.
These questions are the verbatim wording used on live pages that rank for Lake Mary and Florida air-conditioning queries. They are evidence of how the question gets typed, not a capture of Google’s People Also Ask box.
Sources for this page
Researched 6 September 2026. Fees, rebate amounts and code minimums change — check the issuing authority before you rely on a figure.