A common question we are frequently asked is: 

What is the difference between Free Area & Equivalent Area?

The following definitions are from the Technical Guidline Document issued by the Irish Building Regulations 2009.

 Free Area

Equivalent Area

  • The area of a single sharp edged hole that passes the same air volume flow rate at the same applied pressure difference as the vent being tested.

 The Equivalent Area of a ventilator is always less than the Free Area and is a better measure of the airflow performance of a ventilator. 

If you are still unsure as to what you requirements are regarding airflow measurements, then please don't be afraid to contact our technical team anytime.

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