Why “one ton per 500 square feet” is wrong
The rule of thumb you’ll read on forums — one ton of capacity per 400–500 square feet — was designed for a generic house in a generic climate. Your house is not generic. Ceiling height, insulation R-value, window area, orientation, local climate zone, and how many people live there all factor into the real number.
Oversized systems short-cycle (turn on and off too quickly), which means they never run long enough to remove humidity. In a South Carolina summer, humidity is often more uncomfortable than heat. An undersized system runs continuously and never reaches setpoint during peak load days. Both outcomes waste energy and shorten equipment life.
What a proper load calculation includes
ACCA Manual J is the industry-standard method. A proper calculation accounts for:
- Floor area and ceiling height (volume, not just square footage)
- Insulation levels in walls, ceiling, and floor
- Window area, type (single/double pane), and orientation
- Local outdoor design temperatures (cooling and heating)
- Internal heat gains from occupants and appliances
- Air infiltration rate (how leaky the house is)
- Ductwork condition and layout
Typical ranges for Sumter-area homes
As a very rough starting point for central South Carolina:
- 1,200–1,600 sq ft: typically 2–2.5 tons
- 1,600–2,200 sq ft: typically 2.5–3.5 tons
- 2,200–3,000 sq ft: typically 3.5–4 tons
- 3,000+ sq ft: often two systems or a 5-ton unit
These ranges assume average insulation. A well-insulated, recently built home might size down. An older home with single-pane windows and minimal attic insulation might size up.
The right answer: have it calculated
When you call us for a quote, we run a Manual J load calculation on your home — not an estimate based on square footage. That calculation determines the correct equipment size, and we explain our reasoning. If a contractor gives you a quote without asking about your insulation or measuring your windows, that’s a red flag.
Properly sized equipment is more efficient, more comfortable, and lasts longer. It’s worth doing right.