Enter the height of the chimney, the density of the air, the temperature inside the chimney and the temperature outside the chimney into the calculator to determine the chimney draft.

Chimney Draft Formula

The following equation is used to calculate the Chimney Draft.

D = h*p*(1-To/Ti)*g
  • Where D is the chimney draft (pascals)
  • h is the height of the chimney (m)
  • p is the density of the air (1.292 kg/m^3)
  • To is the temperature outside (C)
  • Ti is the temperature inside the chimney
  • g is the acceleration due to gravity (9.81m/s^2)

What is a Chimney Draft?


A chimney draft is a measure of the pressure differential between the inside and outside of a chimney shaft.

How to Calculate Chimney Draft?

Example Problem:

The following example outlines the steps and information needed to calculate Chimney Draft.

First, determine the height of the chimney. For this example, the height is measured to be 15m.

Next, determine the density of the air. This is known to be approximately 1.292 kg/m^3.

Next, determine the temperature inside the chimney. This is measured to be 40C.

Next, determine the temperature outside the chimney. In this case, this is measured to be 30C.

Finally, calculate the chimney draft using the formula above:

D = h*p*(1-To/Ti)*g

D = 15*1.292*(1-(30/40))*9.81

D = 47.529 pascals