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ComfortCalc
A quick rule-of-thumb estimate — a real HVAC installer uses a full Manual J load calculation for precision.
Actual HVAC sizing (a 'Manual J' calculation) accounts for insulation quality, window count and orientation, ceiling height, local climate data, and more — this calculator's BTU-per-square-foot shortcut is useful for a ballpark estimate, not for finalizing an install.
A bigger system isn't simply 'safer' — an oversized AC unit cycles on and off too quickly, cooling the air but not properly removing humidity, leading to a clammy feeling despite a comfortable temperature. Right-sizing matters as much as raw capacity.
System size
36,000 BTU/hr
20 BTU/sq ft is a moderate-climate baseline — hotter climates and poorly insulated homes need more, cooler climates need less. A professional load calculation (Manual J) is more precise.
What you entered
Apply the BTU-per-square-foot rule of thumb
1800 × 20= 36000 BTU/hrConvert to tons of cooling (1 ton = 12,000 BTU/hr)
36000 ÷ 12,000= 3 tonsResult
System size: 36,000 BTU/hr
A 1800 sq ft home needs a roughly 36000 BTU/hr system, or about 3 tons.