Boiler Size Calculator
Estimate the boiler heating output needed for a home based on square footage, insulation quality and ceiling height.
About the Boiler Size Calculator
This calculator gives a simplified estimate of the heating output a boiler needs to deliver, scaling a BTU-per-square-foot rule of thumb by your home's insulation quality and ceiling height.
Formula: Base Load = Square Footage × Load Factor (30 good insulation, 40 average, 50 poor); Adjusted Load = Base Load × (Ceiling Height ÷ 8); Boiler Size (MBH) = Adjusted Load ÷ 1000
MBH (thousand BTU per hour) is the standard rating unit for residential boilers. This rule-of-thumb estimate doesn't account for domestic hot water demand, window area or air infiltration — have a heating contractor perform a full Manual J calculation before purchasing.