Boiler Sizing Calculator
Simplified Boiler Sizing
Quick estimate based on building area and insulation
Formula
Boiler BTU = Area x BTU/sqft x Climate Factor x DHW Factor | 1 BHP = 33,475 BTU/hr
Frequently Asked Questions
How do I size a boiler?
The best method is a Manual J heat loss calculation. As a rough estimate, multiply heated area by 25-35 BTU/sq ft for average insulation and add 20% for domestic hot water.
Should I oversize my boiler?
Avoid oversizing. An oversized boiler short-cycles, reducing efficiency and increasing wear. Size to 110-120% of calculated heat loss at most.
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