Flue Gas Density Calculator
Why Hot Flue Gas Is So Much Lighter Than Air
Flue gas density drops sharply as temperature rises, which is exactly the density difference that drives natural draft in the first place. This calculator applies the ideal gas law directly to find flue gas density at any temperature and pressure.
The Formula
Density = (Pressure × Molar Mass) / (R × Temperature)
R = 8.314 kJ/(kmol.K); typical flue gas has an average molar mass around 28-30 g/mol.
Worked Example
Flue gas at 500 K, standard atmospheric pressure, molar mass 29 g/mol:
Density = (101.325 × 29) / (8.314 × 500) = 0.708 kg/m3
How to Use This Calculator
- Enter the Flue Gas Temperature in Kelvin.
- Optionally enter Pressure (defaults to standard atmospheric) and Molar Mass (defaults to 29 g/mol).
- Select Calculate to get flue gas density.
Related Calculations
Use this density to find stack draft in the Stack Draft Calculator, or check gas density generally in the Gas Density Calculator.