Plant optimization calculator · Updated 17 September 2026
Boiler Stack Loss Calculator — Siegert Loss, Excess Air & Combustion Efficiency
Estimate dry sensible stack loss from flue temperature, combustion-air temperature and dry O₂, while also showing excess air and indicated combustion efficiency.
Inputs
Live results
- Excess air 16.666667%
- Dry stack loss 7.3066667%
- Indicated dry combustion efficiency 92.693333%
- Net stack temperature 160 K
Formula
EA=O₂/(21−O₂); qA=ΔT×[A1/(21−O₂)+B]; η≈100−qA.
Worked example
180°C flue gas, 20°C air and 3% O₂ can be screened in one pass.
Assumptions and limits
- This is a simplified dry-stack screening model, not ASME PTC 4 certification.
- Condensing appliances require latent-heat treatment beyond this dry-loss model.
FAQs
What does this Boiler Stack Loss Calculator calculate?
Estimate dry sensible stack loss from flue temperature, combustion-air temperature and dry O₂, while also showing excess air and indicated combustion efficiency.
Can I use this for a final design?
Use it for screening, diagnostics and opportunity sizing. Validate final design against measured plant data, OEM limits and applicable standards.
Why does the calculator show intermediate results?
Intermediate engineering quantities make bad inputs and unrealistic assumptions easier to spot before a decision is made.