Chimney Draft Calculator

Checking Draft for Smaller Heating Appliances

Residential and small commercial chimneys are typically specified in mm (or inches) of water column rather than Pascals, since the pressures involved are quite small. The underlying physics is identical to industrial stack draft.

The Formula

Draft (mm WC) = Draft (Pa) × 0.10197

Where Draft (Pa) uses the same density-difference formula as industrial stacks.

Worked Example

A 6 m chimney with flue gas at 450 K and ambient air at 293 K:

Draft ≈ 3,463.4 × 6 × (1/293 − 1/450) × 0.10197 ≈ 1.6 mm WC

How to Use This Calculator

Enter the Chimney Height in meters.
Enter Ambient Temperature and Flue Gas Temperature in Kelvin.
Select Calculate to get draft in mm water column.

Related Calculations

Working on a larger industrial stack instead? See the Stack Draft Calculator, or check flue gas temperature after heat recovery in the Flue Gas Temperature Calculator.