The method
Before using the result
- Idealised air-like gas at uniform temperatures and common atmospheric pressure. Real combustion-gas composition, wind and all flow losses are excluded. Not a vent sizing or appliance-safety assessment.
Worked examples
These original training examples illustrate the method for CSIA Certified Chimney Sweep. Use the matching “Load example” button above to explore a variation; example values are not equipment settings or prescribed criteria.
1. Worked example
Explore the ideal buoyancy-pressure effect of height and gas temperature. Compare the simplified model with actual draft measurements and the losses it excludes.
- Effective stack height
- 8 m
- Inside gas temperature
- 150 °C
- Outside air temperature
- 10 °C
- Absolute atmospheric pressure
- 101.325 kPa
- ρoutside = 1.2466441265944506; ρinside = 0.8341894941397108 kg/m³.
- Δp = 9.80665 × 8 × (1.2466441265944506 − 0.8341894941397108) = 32.35838577089819 Pa.
- Outside density: 1.246644 kg/m³
- Ideal inside density: 0.8341895 kg/m³
- Ideal draft pressure: 32.35839 Pa
2. Comparison example
Compare a different supplied condition using the same method. For Chimney Exam, the important check is that the input meaning, units and method assumptions still match the problem.
- Effective stack height
- 8 m
- Inside gas temperature
- 200 °C
- Outside air temperature
- 10 °C
- Absolute atmospheric pressure
- 101.325 kPa
- ρoutside = 1.2466441265944506; ρinside = 0.7460367419321962 kg/m³.
- Δp = 9.80665 × 8 × (1.2466441265944506 − 0.7460367419321962) = 39.274251270384774 Pa.
- Outside density: 1.246644 kg/m³
- Ideal inside density: 0.7460367 kg/m³
- Ideal draft pressure: 39.27425 Pa
Check your understanding
1. Which relationship is used?
Ideal draft = gh(ρoutside − ρinside), using ρ = p/(Rair T) and Rair = 287.05 J/kg·K.
2. Which assumption should you check first?
Idealised air-like gas at uniform temperatures and common atmospheric pressure. Real combustion-gas composition, wind and all flow losses are excluded. Not a vent sizing or appliance-safety assessment.
3. How should you verify a different unit system?
Convert every input to the displayed calculation units first. Equivalent physical inputs must give equivalent results; a unit label alone does not convert a number.
Continue with the matching exam topic
This tool connects to CSIA Certified Chimney Sweep free practice. Work through a question independently, then use the calculation steps to identify where your method differs. The tool stays free whether or not you choose paid preparation.