Calculate stack exit velocity from actual gas flow rate and internal stack diameter, or solve for the flow or diameter needed for a target velocity.

Use flow at the stack exit temperature and pressure (acfm), not standard flow.

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Stack Exit Velocity Formula

The following two example problems outline the steps and information needed to calculate the Stack Exit Velocity.

SEV = VFR / (ฯ€ร—D2/4)

Variables:

  • SEV is the Stack Exit Velocity (ft/min)
  • VFR is the stack volumetric flow rate (ft3/min) 
  • D is the stack diameter (ft) 

To calculate the average exit velocity, divide actual volumetric flow at the exit temperature and pressure by the internal circular area. Standard-condition flow requires conversion before use; this geometry calculation does not verify exhaust design or a universal acceptable velocity range.

How to Calculate Stack Exit Velocity?

The following steps outline how to calculate the Stack Exit Velocity.

  1. First, determine the stack volumetric flow rate (ft3/min). 
  2. Next, determine the stack diameter (ft). 
  3. Next, gather the formula from above: SEV = VFR / (pi*D2/4).
  4. Finally, calculate the Stack Exit Velocity.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

stack volumetric flow rate (ft3/min) = 300

stack diameter (ft) = 4

SEV = VFR / (pi*D2/4) = ?