Sizing

AC sizing and Manual J in Oviedo, Florida

Oviedo's median home has 2,006 sq ft under air, which a rule of thumb sizes at 4 tons and a real Manual J load calculation often sizes at 3 to 3.5. The City of Oviedo requires that ACCA Manual J-2016 calculation with the changeout permit, so in this city a properly sized system is a document you can ask to see.

The arithmetic

Why bigger is the expensive mistake in Oviedo

The rule of thumb people use is one ton per 500 square feet. Applied to Oviedo’s median 2,006 sq ft that gives 4 tons; applied generously it gives 5. A real load calculation on the same house commonly lands lower, and the difference between the two is the difference between a house that is comfortable and a house that is cold and clammy at 74°F.

Here is why, and it is specific to this climate. Central Florida summer air carries sustained dewpoints in the seventies. A large share of the work an air conditioner does here is latent — condensing water out of the air — rather than sensible. Dehumidifying takes run time. An oversized system satisfies the thermostat quickly, shuts off, and never runs long enough to pull the water out. You get 74°F at 60% relative humidity, which feels worse than 76°F at 48% and grows things.

Climate zone: Florida Energy Conservation Code 2023, Chapter 3 — climate zones. Design temperatures commonly cited for Seminole County Manual J work are 93°F summer and 38°F winter.

The inputs

What a Manual J actually measures

What a load calculation looks at, and why it varies across this city
Input	Why it moves the answer in Oviedo
Conditioned floor area and ceiling height	Median 2,006 sq ft citywide, but the top-20 subdivisions run from 1,268 sq ft in Alafaya Woods Unit B to 4,255 in Oviedo Gardens. One city, a 3.4× spread. Kingsbridge alone spans roughly 1,400 to 8,300 sq ft.
Window area, orientation and glazing	Single-pane aluminium in the 1985–96 stock, code-compliant glazing in Live Oak Reserve and later. Often the largest single line.
Insulation	1980s attic insulation that has settled is not what the original build specified.
Duct location and leakage	Attic ducts in a vented attic reaching 130°F. In Alafaya Woods and Twin Rivers the trunk is often original.
Pools and screened decks	4,831 Oviedo parcels have a pool — 39.4% of the stock. A screened deck beside the house adds evaporative moisture load.
Two-system houses	Kingsbridge and Remington Park have genuinely two-system homes; the larger late-80s houses were commonly built with one oversized straight-cool system on a single thermostat, which is exactly the case a real Manual J re-opens.

Seminole County Property Appraiser CAMA extract, Parcels.csv dated 5 September 2026.

What to ask

Four questions that separate the quotes

What to ask for, and what a good answer looks like:

“Can I see the load calculation you filed with the City?” A real one has your address on it and the inputs listed. “It is a four ton, same as what is there” is a transcription, and in Oviedo it is also an incomplete permit application.
“What is the existing external static pressure?” A measured number in inches of water column. If the ducts cannot pass the airflow, the tonnage on the sticker is fiction.
“What is the sensible heat ratio of the proposed equipment?” In a latent-load climate this matters as much as tonnage. A variable-capacity system that runs long at part load is often the better answer than a larger single-stage one.
“Was the old system oversized?” If it was, matching it repeats the mistake with a newer warranty on it.

Being sold a bigger system than the one you have?

Ask for the load calculation before you ask for the price. In this climate the smaller correct answer is usually the more comfortable one.

Call (321) 415-3018 Send the address and build year

The question this page answers

How do I know my AC is sized properly?

In Oviedo you have a document to point at. The City’s HVAC Change Out Permit Application Guidelines require a copy of the equipment sizing calculations — ACCA Manual J-2016, or another approved heating and cooling calculation methodology for residential work — uploaded with the application. Ask your contractor for the Manual J they filed. If it does not exist, the application was incomplete.

Why it matters more here than in a dry climate: Oviedo is IECC Climate Zone 2A, hot-humid. The dominant load is latent — moisture, not temperature. An oversized system satisfies the thermostat fast, shuts off before it has pulled the humidity down, and leaves the house cold and clammy. Bigger is not a safety margin here; it is the defect.

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