Why square-footage rules of thumb oversize HVAC equipment

Sized by the 500 ft²/ton rule a 2,000 ft² home gets 4 tons; the real load is ~1.75 tons. Rules of thumb oversize 2–3× — and oversized short-cycles.

A bar chart comparing two ways to size the same 2,000-square-foot home. The 500-square-feet-per-ton rule of thumb gives a 4-ton system, while an actual Manual J load calculation gives about 1.75 tons — roughly 2.3 times smaller. Real load calcs average around 1,400 square feet per ton, so rules of thumb oversize by two to three times, and an oversized unit short-cycles and fails to dehumidify. — Source: Energy Vanguard (avg 1,431 ft²/ton)

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A bar chart comparing two ways to size the same 2,000-square-foot home. The 500-square-feet-per-ton rule of thumb gives a 4-ton system, while an actual Manual J load calculation gives about 1.75 tons — roughly 2.3 times smaller. Real load calcs average around 1,400 square feet per ton, so rules of thumb oversize by two to three times, and an oversized unit short-cycles and fails to dehumidify.

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