Most replacement systems should be the same size as the one they replace, as long as that one kept the house comfortable. If it did, start with method 1. If it never kept up, or you've added rooms, use method 2 and have your installer run a load calculation.
Method 1: read the size off your current unit
The tonnage is hidden in the model number on the outdoor unit's data plate. Look for a three-digit number like 024, 036 or 048. That's the cooling capacity in thousands of BTU, and every 12,000 BTU is one ton.
Model number decoder
Type the model number from your outdoor unit's label.
| Code in model number | BTU | Size |
|---|---|---|
| 018 | 18,000 | 1.5 ton |
| 024 | 24,000 | 2 ton |
| 030 | 30,000 | 2.5 ton |
| 036 | 36,000 | 3 ton |
| 042 | 42,000 | 3.5 ton |
| 048 | 48,000 | 4 ton |
| 060 | 60,000 | 5 ton |
Some brands drop the leading zero, so 36 or 48 inside the model number means the same thing. If you can't find it, send us a photo of the data plate and we'll read it for you.
Method 2: estimate from your home
Size estimator
A rule-of-thumb estimate based on the area you cool and a few things that change the load.
This is an estimate, not a load calculation. The proper way to size a system is an ACCA Manual J calculation, which accounts for every wall, window and duct run. Ask your installer for one, especially if you're changing size. An oversized AC cools fast but leaves a Florida house damp and clammy, and an undersized one runs all afternoon without catching up.
Why bigger isn't better
In a humid climate, an AC removes moisture only while it runs long enough for the coil to get cold and drain. An oversized system hits the thermostat setting in a few minutes and shuts off before it has pulled much water out of the air. The result is a cool but sticky house, more on-off cycles and more wear on the compressor. If you're between two sizes and the house is well insulated, the smaller one is usually the better call. Your installer can confirm it.
When the answer is "two systems"
Above about 5 tons, residential equipment tops out. Larger homes, or homes with a second floor that never cools down, are usually better served by two smaller systems or a central system plus a ductless mini-split for the problem area.
Next steps
- Check your ductwork can carry the airflow of the size you pick. Going up a size on old ducts often doesn't work.
- Pick a matched condenser and air handler. Our AHRI match checker confirms the rating of any pair.
- Not sure? Send us your current model number and square footage at sales@hvacsupplypro.com or call (239) 266-9766, Mon–Fri 8am–5pm ET.