AC sizing guide: why “bigger is better” ruins Houston homes

What a “ton” of cooling means

A ton of air conditioning is 12,000 BTU per hour of cooling capacity — a term left over from the ice era. Residential systems come in half-ton steps from 1.5 to 5 tons. The question every install answers: how many tons does your house need?

Why the square-foot rule fails in Houston

The old rule — "one ton per 500–600 square feet" — ignores insulation, window area and orientation, ceiling height, duct leakage, and shade. Two 2,400 sq ft houses in Cypress can legitimately need 3 tons and 4.5 tons. In Gulf Coast humidity, guessing wrong in either direction is expensive.

What oversizing actually does

• Short-cycling. An oversized unit cools the air fast, shuts off, and repeats. It never runs long enough to dehumidify — the house reads 72°F and feels sticky.
• Higher bills. Startup is the most power-hungry moment of the cycle; more starts means more energy for less comfort.
• Shorter equipment life. Compressors die from starts, not from hours. Short-cycling can cut compressor life in half.
• Hot and cold spots. Short cycles never push conditioned air to the far rooms.

How Manual J sizing works

Manual J is the industry-standard load calculation: square footage, insulation levels, window count and orientation, air leakage, duct location, occupancy, and local design temperatures (for Houston: 95°F summer design with extreme humidity). The output is the capacity your house needs — usually to the half-ton. It takes 30–45 minutes on site and it is the difference between engineering and guessing.

What to ask your installer

One question separates real installers from box-swappers: "Will you run a Manual J on my home?" If the answer is "we match what's there" or "we've always used X tons in this neighborhood," keep calling around.