What Size Air Conditioner Do I Need? Why Bigger Is Not Better
The most consequential decision in a new installation isn't the brand — it's the size. And the most common contractor error is going too big.
Tons and BTUs, quickly
One ton equals 12,000 BTU per hour of heat removal. Residential systems typically run 1.5 to 5 tons. The old rule of thumb — 500 to 600 square feet per ton — is only a rough starting point and ignores everything that actually matters.
Why oversizing hurts
An oversized air conditioner satisfies the thermostat fast and shuts off. That sounds good until you realize dehumidification requires runtime. Short cycles leave your home cold and clammy, they wear out the compressor with constant starts, and they create uneven temperatures because air never circulates long enough to mix. Oversized systems cost more upfront and more to run.
Why undersizing hurts
An undersized unit runs continuously on design days and still can't hold setpoint, which drives up bills and shortens equipment life from nonstop operation.
What a real load calculation includes
- Conditioned square footage and ceiling heights
- Insulation values in walls, attic and floors
- Window area, glazing type and orientation
- Air infiltration and building tightness
- Duct location and measured leakage
- Occupancy, appliances and internal heat gains
- Local design temperatures
That's a Manual J calculation, and it's included free with every installation estimate we provide. If a contractor sizes your system off square footage alone in a two-minute walkthrough, get a second quote.
Rough starting points
| Home size | Typical range |
|---|---|
| 1,000 – 1,200 sq ft | 2 – 2.5 tons |
| 1,200 – 1,600 sq ft | 2.5 – 3 tons |
| 1,600 – 2,100 sq ft | 3 – 3.5 tons |
| 2,100 – 2,600 sq ft | 3.5 – 4 tons |
| 2,600 – 3,200 sq ft | 4 – 5 tons |
Starting points only — insulation, glass and climate routinely shift these by a full ton.
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