A new air conditioner is a big purchase, and the quotes for one can disagree on the most basic number: how big it should be. If one quote matches the old unit, another goes up a size, and the last names a size after a quick walk around the house, which one is right for your Palm Beach Gardens home?
The right size is calculated for your house. It isn’t read off the square footage or copied from the old unit’s label. Below, we walk through how that calculation works, why the local climate and the state’s own rules change the answer, and what a sizing quote should show before you sign for an AC installation.
How Is the Right AC Size Worked Out for a Palm Beach Gardens Home?
In two steps: work out how much heat and moisture the house takes on during the kind of hot day the system is designed for, then choose equipment whose capacity matches that load. For new homes, Florida’s energy code spells out the method in Section R403.7.1 of the Florida Building Code, Energy Conservation, 8th Edition (2023), which the Florida Building Commission lists as effective December 31, 2023. That section has equipment sized with Manual S from the Air Conditioning Contractors of America (ACCA), based on loads calculated with Manual J or another approved calculation method.
The next section of the 8th Edition, R403.7.1.1, sets how close the match has to be for a cooling-only system in a new detached home. Its total capacity can’t be less than the calculated total load, and it must be “not more than 1.15 times greater than” that load, or the closest available size in the manufacturer’s product lines. For attached single- and multiple-family homes, such as townhomes and condominium units, one of the section’s exceptions allows a cooling capacity as low as 80 percent of the calculated total sensible load.
The 9th Edition (2026) of Florida’s energy conservation code takes effect December 31, 2026. The analysis of changes for that edition, posted on the Florida Building Commission’s website, says it revises R403.7.1 and R403.7.1.1, including how a cooling-only system’s capacity is chosen.
Capacity is sold in tons. One ton of cooling equals 12,000 BTU per hour, and home central air conditioners typically come in half-ton steps from 1.5 to 5 tons, as Carrier’s sizing guide lays out. The calculation gives a load in BTU per hour, and the equipment choice lands on one of those steps.
Two inputs make the calculation local to the Gardens: the outdoor design temperature for a home’s location, and the moisture a South Florida house has to shed. Both are covered below.
Why Does Square Footage Alone Get AC Sizing Wrong?
Because floor area is only one of the things that bring heat into a house. The usual rough estimate is about 20 BTUs per square foot of living space, and insulation and climate will alter that number, so it is a ballpark figure only.
By our arithmetic, that rule gives a 2,000-square-foot house 40,000 BTU per hour, which at 12,000 BTU per ton falls between the 3-ton and 3.5-ton steps. Yet a 2,000-square-foot house typically requires a 3-ton air conditioner (36,000 BTU per hour), high ceilings or poor insulation may call for a larger unit, and an HVAC professional can confirm the exact requirement. So the per-foot rule doesn’t even land on a standard size, and neither figure can tell you whether a 3-ton system will cool that particular house.
The University of Florida’s IFAS Extension (UF/IFAS) puts it plainly in its publication Energy Efficient Homes: Air Conditioning, revised in January 2025: to assure proper sizing, the load “must be calculated” and not “just estimated based on square feet.” It says load calculations rest on the exact area, orientation and type of construction of each part of the house’s outer shell, plus the heat given off by the lights, people and equipment inside.
For example, two Gardens houses with the same floor area can differ on each of those counts: which way the big windows face, how well the attic is insulated, how many people live there. A per-square-foot rule sees none of it.
What Does a Manual J Load Calculation Check in Palm Beach Gardens?
The house itself, piece by piece, and the weather it has to hold out against. The U.S. Department of Energy’s fact sheet on right-sizing equipment (January 2002) says Manual J works out the design loads from:
- the amount of wall, ceiling, window and floor area, and their insulation value;
- how much air leaks through the building’s shell and through the ducts;
- and, as factors that can also make a difference, the building’s orientation, its roof surface color and its occupancy.
Then comes the weather. For Palm Beach County, which takes in the Gardens, ENERGY STAR’s County-Level Design Temperature Reference Guide (2015) lists a 1% cooling design temperature of 91°F, the most a load calculation may use there for a home certified under the ENERGY STAR Certified Homes program. The same guide recommends the Manual J design temperature for the weather location closest to the home, so a calculation for a Gardens house should show which outdoor figure it used.
The result comes in two parts: a temperature load and a moisture load. In Palm Beach Gardens, the moisture part is where sizing gets interesting.
How Does Palm Beach Gardens Humidity Change the Size an AC Needs?
It gives the system a second job. Here, an air conditioner has to dry the air as well as cool it, and the drying takes a real share of the work. A 2007 report to the Florida Building Commission on energy efficiency and moisture control cites a reference comparison in which the latent (moisture) portion of the energy used to cool the same house over a season was 0% in Phoenix, Arizona, and 20% in Florida.
That is why the 8th Edition (2023) of Florida’s energy code checks moisture separately. For a new detached home, its section R403.7.1.1 says the equipment’s latent capacity “shall not be less than the calculated latent load.” So tonnage alone doesn’t settle the size: the moisture side has to be checked too.
Humidity also pushes the right size toward the calculated load, not past it. UF/IFAS says that sizing the air conditioner close to the actual cooling load provides better humidity control than an oversized unit with the same performance characteristics, because more of the run time is spent with the coil at its coldest, allowing more condensate to form and drain away. Bigger is not the humid-climate fix.
Efficiency ratings are a separate question, and our guide to what a SEER2 rating means for a Palm Beach Gardens replacement covers them.
What Goes Wrong When an AC Is Oversized for a Palm Beach Gardens House?
It cools the rooms before it dries them. UF/IFAS says an over-sized air conditioner will cool your home too quickly to remove moisture very effectively, and that the result is a home that is cool but “clammy.” The quick on-and-off runs that come with too much capacity are short cycling, which our Jupiter guide to why an AC keeps short cycling covers, including what the repeated starts do to the equipment. An undersized system fails the other way: it runs continuously, struggling to reach your set temperature.
Can a Replacement Simply Match the Old Unit’s Tonnage in Palm Beach Gardens?
It can, and the city’s change-out paperwork records the tonnage either way. But the old number is a starting point, not an answer.
Finding the current size is the easy part. Most manufacturers code the nominal capacity into the model number on the outdoor unit’s label, as a 2- or 3-digit section in thousands of BTU per hour. By that code, 048 means 48,000 BTU per hour, which at 12,000 BTU per ton works out to 4 tons. That label figure is nominal, though, and the unit’s actual capacity will almost certainly be different.
Copying that number assumes two things: that it was right when it went in, and that the house hasn’t changed since. Neither is a given. The old size may itself have been copied from the unit before it, with no calculation behind either one. And houses do change. UF/IFAS lists sealed ductwork, windows, insulation and sealing against outside air leaks among the features that reduce a house’s air conditioning load, so a Gardens house with new windows or added attic insulation may need less capacity than the old unit was chosen for.
Florida law points the same way. Section 553.912 of the Florida Statutes says it is the intent of the Legislature that all replacement air-conditioning systems in residential applications be installed using energy-saving, quality installation procedures, “including, but not limited to, equipment sizing analysis and duct inspection.” It states that as intent, and the same section adds that existing equipment in residential applications need not meet the minimum equipment efficiencies, “including system sizing and duct sealing.”
Then there is the permit paperwork. The City of Palm Beach Gardens’ A/C Change-Out Compliance Form asks for the manufacturer, the model numbers and the size in tons of both the replacement system and the existing one, and it has no line for a load calculation. The form records the tonnage. It doesn’t ask how the tonnage was chosen.
Two-story homes, where one floor runs hotter than the other, raise separate questions about air distribution and zoning that sit outside this guide.
What Should a Palm Beach Gardens AC Quote Show About Sizing?
The calculation behind the size, not just the size. UF/IFAS tells homeowners to request a load calculation and says it “will require taking measurements in your house and asking questions.” It also advises against using a contractor who wants to size the system solely on the square footage of the house.
That gives you a simple test on the day of the visit. A load calculation leaves a trail: measurements taken, questions asked about how the house is used, and a report built on your home’s own numbers. A guess leaves a tonnage. If a size is named from the driveway, or the numbers behind it aren’t on offer, you’ve learned something about the quote.
ENERGY STAR’s installation bid comparison checklist lists questions to put to each contractor, and three of them bear on size: whether the contractor will measure your home and calculate the correct size using Manual J, whether they will test the maximum system size your existing ductwork can take, and whether they will leave documentation after installation that includes the Manual J calculations and the AHRI certificate.
Put together, a sizing quote you can check shows four things:
- The load and its inputs. A Manual J result for your house, with the total load, its moisture part, and the outdoor design temperature it used.
- The equipment’s capacity at those conditions. For a new detached home, the 8th Edition (2023) of Florida’s energy code calls the AHRI total capacity “a nominal, rating-test value” that is not to be used for sizing, and requires the manufacturer’s expanded performance data to select cooling-only equipment.
- A match inside the code’s window. For a new detached home, the 8th Edition (2023) standard for a cooling-only system is total capacity between the calculated total load and 1.15 times it, or the closest size made, with latent capacity no less than the latent load (attached homes, such as townhomes and condominium units, have their own exceptions). It makes a fair yardstick for a replacement quote too.
- A duct check. Whether the existing ducts can carry the size being proposed.
We diagnose the whole system, ductwork included, before quoting a replacement.
The Bottom Line
- The right size comes from a load calculation for your house, matched to equipment that fits it. Square footage is a ballpark that can land between two standard sizes.
- In the Gardens, the calculation uses a local outdoor design temperature (ENERGY STAR’s guide says the most it may use is 91°F for homes certified under its program in Palm Beach County) and has to carry a moisture load as well as heat.
- Humidity pushes the right size toward the calculated load, not past it. An oversized AC cools before it dries and leaves the house clammy.
- The old unit’s tonnage is a starting point. Florida’s statute states sizing on replacements as an intent, and the city’s change-out form records the tons without asking how they were chosen.
- A sizing quote you can check shows the load and its inputs, the equipment’s capacity at those conditions, how close the match is, and whether the ducts can carry it.
If you’re weighing a replacement in Palm Beach Gardens, book a visit. We always put a repair option on the table, even when we are recommending a replacement.
