What Size AC You Need, and why bigger loses.
Sizing is the decision that most affects whether you are comfortable, and the one most often done by rule of thumb. Here is what a proper calculation involves — and what oversizing actually costs you.
How sizing is worked out
Sizing is the decision that most affects whether you are comfortable, and the one most often done by rule of thumb. Here is what a proper calculation involves — and what oversizing actually costs you.
What a "ton" means
A unit of cooling capacity, not weight — one ton equals 12,000 BTU per hour. It describes how much heat the system can remove, which is why matching it to your home matters so much.
Why oversizing backfires
A too-large system reaches temperature fast and shuts off, never running long enough to pull moisture out. You end up with a cold, damp house, more wear from constant starting, and a higher bill.
Why undersizing fails too
A system that can never catch up runs continuously on the hottest days, wearing out sooner and still leaving you uncomfortable when it matters most.
Square footage is a starting point
It is one input among many. Two identical-sized homes can need different systems depending on glass, shade, insulation and layout. A quote based on floor area alone is a guess.
What a load calculation includes
Orientation and window area, insulation levels, ceiling heights, duct condition, air leakage, and how the home is actually used. That is what produces a defensible number.
Ductwork sets the ceiling
Ducts that cannot carry the airflow will cap what any system delivers. Sizing the equipment without assessing distribution is how homes end up with expensive, disappointing systems.
The right size is the one calculated from your house. Everything else is a guess someone else has to live in.
United A/C & RefrigerationWhy oversizing is the common error
Almost every sizing mistake in this climate errs in the same direction, and it feels generous rather than wrong. An oversized system cools the air quickly, satisfies the thermostat, and shuts off — before it has run long enough to pull meaningful moisture out. The house ends up cold and clammy, which people then try to fix by setting the temperature lower, which makes the cycling worse. Short cycling also increases wear, since starting is the hardest thing a compressor does. Proper sizing is a calculation rather than a rule of thumb: floor area, ceiling height, window area and orientation, insulation, occupancy and duct condition all feed into it. Square footage alone is the shortcut that produces the problem. If your home cools quickly but never feels dry, sizing is a more likely explanation than a fault, and it is worth resolving before replacing anything or adding humidity control.
Floor area is a single input among several, since glass, orientation, insulation and duct condition all change the result. A capacity quoted without anyone seeing the home is a guess, paid for in comfort and equipment life.
Humidity is why oversizing fails here
In a dry climate, an oversized system is merely wasteful. In Florida it actively fails at its job. Cooling the air is only half the work here; removing moisture is the other half, and moisture removal needs sustained run time. A system with more capacity than the house requires satisfies the thermostat quickly, shuts off, and leaves a house that is cold and clammy. We see the consequences most in the large two-storey master-planned homes of Coral Springs and Parkland, where the temptation to size generously is strongest and where zones behave very differently from one another. At the other extreme, the compact mid-century houses of Wilton Manors leave so little space that equipment has to be measured to fit before capacity is even discussed.
Serving Broward County and southern Palm Beach County from our shop in Deerfield Beach.
Measured,
not estimated.
We look at the actual house
Glass, orientation, insulation, ceiling height and layout all change the load. That requires being in the home, which is why the free estimate is an in-person visit rather than a phone quote.
We assess the ductwork
Distribution determines what any system can actually deliver. If the ducts are the limiting factor, we say so before you spend money on equipment that cannot overcome them.
We size for humidity, not just heat
In this climate the system must run long enough to dehumidify. That consideration often argues for slightly less capacity than a rule of thumb would suggest — and a much more comfortable house.
Questions and answers
Can you tell me what size I need over the phone?
Not honestly. Square footage is only one input; glass, orientation, insulation and ductwork all change the answer. Anyone quoting a size without seeing the home is guessing, and the cost of guessing wrong is comfort and equipment life.
My old system was a certain size. Should the new one match?
Not automatically. The original may have been sized incorrectly, and the home may have changed — new windows, insulation, additions. It is a data point worth knowing, not a specification to copy.
What happens if my AC is oversized?
It short-cycles: cooling quickly, shutting off, and never running long enough to remove humidity. The result is a house that feels cold and clammy, plus more wear from frequent starts and a higher bill.
Is a bigger system better for extreme heat?
No. Correct sizing handles design conditions by definition. Oversizing to feel safe produces worse humidity control year-round in exchange for a marginal benefit on a handful of days.
Do ceiling height and windows really matter?
Considerably. High ceilings increase the volume to condition, and west-facing glass can add a substantial afternoon load. Two homes with identical floor area can genuinely need different systems.
Our house is bigger than average. Does that automatically mean more tonnage?
Not automatically. Floor area is one input among several, and a large, well-shaded, well-insulated house with modest glazing can need less capacity than a smaller house with heavy western exposure. What usually matters more in a large home is how the capacity is divided between zones, because one correctly sized system serving an area it cannot reach will underperform regardless of its rating.
Can a system be too small?
It can, though it is much rarer here than oversizing. An undersized system runs continuously and still fails to hold temperature on the hottest afternoons, which is fairly obvious once you see it. The reason oversizing is the more common error is that it looks like generosity and its symptoms — humidity, short cycling, uneven comfort — are easy to blame on something else.
How we know this
This advice comes from what our technicians actually find on service calls in Broward County and southern Palm Beach — not from national HVAC copy. Salt-air corrosion on the barrier island, drain lines that block every wet season, and equipment running nine months a year are local realities, and they change the right answer.
Worth disclosing: we install Amana equipment, so we are not an independent reviewer. Where a brand or product is discussed we say what it is good and bad at, and we will tell you when the honest answer is to repair what you have or do nothing yet.
Talk to a technician
Have a question this raised? The assistant answers what it can, takes your details, and hands you to a real person who confirms the day and time.