HVAC Sizing Calculator

HVAC sizing uses a base BTU-per-square-foot estimate, adjusted for climate zone and insulation quality.

Base BTU = Square Footage × BTU per Sq Ft

Adjusted BTU = Base BTU × Climate Factor × Insulation Factor

Tonnage = Adjusted BTU / 12,000

Unit conversions:

• Imperial: Enter square feet
• Metric: Enter square meters (1 m² = 10.764 sq ft)

BTU per square foot baseline: 20 BTU/sq ft (moderate climate, average insulation)

Climate zone factors:

• Zone 1–2 (Hot/Humid — FL, TX, AZ): 1.25×
• Zone 3 (Warm — GA, SC, CA coast): 1.10×
• Zone 4 (Mixed — VA, TN, MO): 1.00×
• Zone 5 (Cool — IL, PA, CO): 0.95×
• Zone 6–7 (Cold — MN, WI, ME): 0.90×

Insulation factors:

• Poor insulation (older homes, no upgrades): 1.20×
• Average insulation: 1.00×
• Good insulation (newer construction, well-sealed): 0.85×

Important: This is a rough estimate. A professional Manual J calculation considers windows, orientation, occupancy, and ductwork for precise sizing.