How to Calculate Heat Loss
What is Heat Loss?
Heat loss calculation determines heating requirements based on insulation, air leakage, and temperature difference. Critical for system sizing.
Formula
Conductive loss: Q = U × A × ΔT (sum all surfaces)
- Q
- 1 — 1
- U
- U value — Variable used in the calculation
- A
- A value — Variable used in the calculation
Step-by-Step Guide
- 1Conductive loss: Q = U × A × ΔT (sum all surfaces)
- 2Infiltration loss: Q = 1.08 × CFM × ΔT × air density
- 3Total loss drives heating system size
Worked Examples
Input
House 200 m², U-avg 0.5, ΔT 20K, 500 CFM infiltration
Result
Total loss ~12 kW (heating system needed)
Detailed calc required
Common Mistakes to Avoid
- ✕Neglecting infiltration (often 30-50% of total loss)
- ✕Using design temperature without seasonal variation
Frequently Asked Questions
Why is air sealing important?
Infiltration loss often exceeds conductive loss; air sealing improves efficiency more than adding insulation.
Does orientation affect heat loss?
Indirectly; south-facing gains solar heat. Window orientation matters more than walls.
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