What Size AC Do I Need for My Savannah Home?
By Bryan Donaldson, Owner, On Time Air. 25+ years of HVAC experience in Savannah, GA.
Here’s a question I get on almost every replacement estimate: “The old one was a three ton, so we just want another three ton, right?”
Maybe. But that assumes whoever sized the original got it right, and in my experience a meaningful percentage of systems in this area are the wrong size. Usually too big.
Which sounds like it shouldn’t be a problem. Bigger air conditioner, colder house. That’s not how it works, and in Savannah specifically, an oversized system creates a problem you’ll feel every single day.
The Rule of Thumb, and Why It’s Not Enough
You’ve probably seen the standard formula: 20 BTU per square foot, or roughly one ton of cooling per 500 to 600 square feet.
For a 2,000 square foot home, that math gives you about 3.5 tons.
It’s a starting point. It is not an answer. That formula treats a 1920s bungalow in Ardsley Park with original windows and a 2023 build in Pooler with spray foam and double-pane glass as the same building. They are not remotely the same building.
Two houses of identical square footage on the same street can have cooling loads that differ by a full ton.
What Actually Determines Your Cooling Load
A proper sizing calculation accounts for:
Insulation levels in the attic, walls, and floor. Attic insulation matters enormously here, because a Savannah attic hits 130 degrees or more in July.
Windows. Number, size, orientation, single versus double pane, and whether they have low-E coating. West-facing glass is the single biggest afternoon load in most homes.
Air infiltration. How leaky the house is. Older homes downtown often have significant infiltration, which brings humid outside air in continuously.
Ceiling height. Vaulted ceilings and the twelve-foot ceilings in a lot of Savannah’s historic homes mean more air volume to condition.
Orientation and shade. A home shaded by live oaks has a materially lower load than one in full sun.
Occupancy and appliances. Each person adds heat. So does cooking, laundry, and a wall of electronics.
Ductwork. Where the ducts run and how well they’re sealed. Ducts in an unconditioned attic lose capacity before the air ever reaches a room.
The industry method for putting numbers to all of that is called a Manual J load calculation. It’s published by ACCA, it’s the standard every reputable contractor should be using, and it produces a real number rather than a guess.
Why Oversizing Is the Bigger Mistake Here
In a dry climate, an oversized AC is mostly a waste of money. In coastal Georgia, it actively makes your home uncomfortable. This is the part I wish more homeowners understood.
Air conditioning does two jobs. It lowers temperature, and it removes moisture. The moisture removal happens because humid air passes over a cold evaporator coil, water condenses on it, and that water drains away.
That process takes time. The coil has to stay cold, and air has to keep moving across it.
An oversized system cools the air fast, hits the thermostat setpoint, and shuts off. Short cycling. It might run eight minutes at a stretch instead of twenty. It never runs long enough to pull meaningful moisture out of the house.
The result is a home that’s 72 degrees and clammy. You lower the thermostat trying to fix it, the system short cycles harder, and now you’re at 68 degrees and still feel sticky. Meanwhile you’re paying to run a compressor that starts and stops all day, which is where most of the wear and most of the electricity goes.
Add the mold and mildew risk that comes with sustained indoor humidity above 60 percent, and oversizing stops being an efficiency question and becomes a home health question.
A correctly sized system runs longer, gentler cycles. It’s quieter, it costs less to run, it lasts longer, and critically, it dehumidifies.
What Undersizing Looks Like
It’s less common, but it happens, usually after someone adds square footage without touching the HVAC.
Signs: the system runs almost continuously on hot afternoons, never quite reaches the setpoint on the worst days, and rooms farthest from the air handler stay warm. Your power bill is high because the compressor essentially never stops.
There’s a nuance here. A system that runs long cycles in July is not automatically undersized. Systems are designed to run nearly continuously on the hottest few days of the year. That’s correct behavior, not a defect.
Typical Sizes for Savannah Homes
Rough ranges we see locally, assuming reasonable insulation and average window area:
| Home size | Typical range |
|---|---|
| 1,000 – 1,300 sq ft | 2 to 2.5 tons |
| 1,300 – 1,700 sq ft | 2.5 to 3 tons |
| 1,700 – 2,200 sq ft | 3 to 3.5 tons |
| 2,200 – 2,800 sq ft | 3.5 to 4 tons |
| 2,800 – 3,500 sq ft | 4 to 5 tons |
Treat these as a sanity check on a quote, not a specification. An 1,800 square foot poorly insulated home with a lot of west glass can genuinely need more than a well-built 2,400 square foot home.
The Question to Ask Any Contractor
When you’re getting replacement quotes, ask this: “Are you performing a Manual J load calculation, or sizing off the existing equipment?”
The answer tells you a lot.
If a contractor measures rooms, counts and measures windows, asks about insulation, and looks at your ductwork, they’re doing it properly. If someone glances at the nameplate on your old unit and writes a number on a quote, they’re replacing a guess with the same guess.
There’s one legitimate exception. If the existing system has genuinely performed well for a decade, held temperature on design days, and kept humidity in check, that’s real-world evidence worth weighing. Good contractors use that as a cross-check against the calculation, not as a replacement for it.
Where Variable-Speed Equipment Changes the Math
Modern variable-capacity systems shift this conversation somewhat. Instead of being simply on or off, they modulate output, often running at 30 to 100 percent of capacity.
For our climate that’s a real advantage. A variable-speed system can run long, low-output cycles on a mild day, which is exactly what you want for dehumidification. They’re more forgiving of slight oversizing and they hold humidity far better than single-stage equipment.
They cost more up front. In a humid coastal climate, they’re worth serious consideration, particularly if you’ve fought humidity in your home before.
Frequently Asked Questions
Can I just replace my AC with the same size? Sometimes, but verify first. If the old system was mis-sized, you’d be repeating the error for another 15 years. Home improvements like new windows, added insulation, or attic sealing also lower your load, meaning you may need less capacity than before.
What is a Manual J load calculation? It’s the ACCA industry-standard method for calculating a home’s heating and cooling load based on its actual construction, orientation, insulation, windows, and air leakage rather than square footage alone.
Is a bigger AC better for Savannah’s heat? No. Oversizing causes short cycling, which prevents proper dehumidification. In our humidity that leaves the house feeling clammy even at a low thermostat setting, and it shortens equipment life.
How many square feet does one ton of AC cool? Roughly 500 to 600 square feet as a rule of thumb, but actual capacity depends heavily on insulation, windows, ceiling height, and ductwork. Use it as a rough check only.
Does ductwork affect what size system I need? Yes, significantly. Undersized or leaky ducts limit how much conditioned air reaches your rooms. Installing a larger system on inadequate ductwork doesn’t solve the problem and often makes airflow issues worse.
Get It Sized Right
If you’re planning a replacement, we’ll perform a proper load calculation and show you the result. If the answer is that you need less equipment than you have now, we’ll tell you that too.
Serving Savannah, Pooler, Richmond Hill, Rincon, Tybee Island, Wilmington Island, and all of Chatham, Effingham, and Bryan counties.
Call On Time Air at 912-210-4901 or request an estimate.
Related: Air conditioning repair and installation, 3 signs it’s time for a new AC, and heat pumps versus air conditioners.