Choosing the right air conditioner size is the most important decision in your installation. An undersized unit will run constantly and fail to cool your home. An oversized unit will cycle on and off, leaving humidity high and comfort low. Here’s how to determine the correct size.
Understanding AC Sizing: AC capacity is measured in tons or BTUs. One ton equals 12,000 BTUs. A typical 2,000‑square‑foot home might require a 3‑ton system. But square footage alone is not enough—you need a proper load calculation.
Factors That Determine Size:
- Square footage and ceiling height
- Climate zone (USA climate zones vary significantly)
- Insulation levels
- Number and quality of windows
- Heat‑generating appliances and occupants
- Ductwork condition and leakage
Manual J Load Calculation: A professional contractor performs a Manual J calculation to precisely determine the cooling load. This is the industry standard and ensures optimal comfort and efficiency. Never accept a contractor who sizes based on square footage alone.
Consequences of Improper Sizing: An oversized unit short‑cycles, fails to dehumidify, and wears out faster. An undersized unit runs constantly, can’t keep up on hot days, and drives up energy bills. For related installation mistakes, see common AC installation mistakes. For the full installation process, see what to expect during AC installation. For costs, see AC installation cost. For permits, see permits and codes.
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