Boiler Sizing Calculator
Size heating boilers based on building heat loss, domestic hot water load, pickup factor, efficiency, and altitude derating.
Inputs
BTU/hr
Typical residential: 30,000–100,000 BTU/hr; commercial: 100,000+ BTU/hr
BTU/hr
%
%
Standard boiler: 80–85%; ENERGY STAR: ≥90%; condensing: 90–98% per ASHRAE 90.1
ft
Results
Gross Input Required
175,882 BTU/hr
Required Boiler Rating
175,882 BTU/hr
Net Output Required130,000 BTU/hr
Fuel Consumption1.76 therms/hr
Est. Annual Fuel Cost$4,221.00
How to Use This Calculator
- Enter Building Heat Loss, Domestic Hot Water Load, and Pickup Factor.
- Set Combustion Efficiency and Altitude.
- Review Gross Input Required (BTU/hr) and Required Boiler Rating (BTU/hr).
- Use Net Output Required (BTU/hr) and Fuel Consumption (therms/hr) to inform your decision.
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