Combi Boiler Sizing Guide

General Sizing Guidelines by Home Size

These are approximate guidelines only. Actual BTU requirements depend on your home's insulation, window efficiency, ceiling height, and exposure to wind and sun.

• Under 1,500 sq ft — 60,000–80,000 BTU/h (small condos, apartments)
• 1,500–2,500 sq ft — 80,000–120,000 BTU/h (typical Vancouver homes)
• 2,500–3,500 sq ft — 120,000–150,000 BTU/h (larger family homes)
• 3,500+ sq ft — 150,000–200,000+ BTU/h (large homes, multi-zone)

Why Professional Heat Loss Calculation Matters

Professional contractors perform a detailed heat loss calculation (using the CSA F280 standard in Canada or Manual J in the US) before recommending a boiler size. This calculation accounts for:

• Wall, ceiling, and floor insulation levels and R-values
• Window size, glazing type, and orientation
• Air leakage and infiltration rates
• Local climate data for your specific Vancouver area
• Ceiling heights and room volume
• Hot water demand — number of bathrooms and fixtures

Oversizing vs Undersizing

Both oversizing and undersizing create problems. An oversized boiler cycles on and off frequently (short-cycling), which wastes energy, increases wear on components, and fails to maintain even temperatures. An undersized boiler runs continuously and can't maintain setpoint on the coldest days.

Modern modulating boilers can adjust their output to match demand, which helps mitigate mild oversizing. However, significant oversizing still causes efficiency and comfort issues.

Frequently Asked Questions