# Commercial Ventilation Calculation - How Many Whirlybirds?

**STEP 2**

**VOLUME OF SHED/WAREHOUSE/FACTORY**

To work out the volume of the premises that needs ventilating, simply gather the measurements that are required for the calculation. In the this case we need the Length, Width and Height all in metres.

*(Note: The image to the left illustrates where the measurements should be taken from)*

With the figures, simply enter them in to the equation below.

**Volume (m³) = Length (m) x Width (m) x Height (m)**

**STEP 3**

**REQUIRED NUMBER OF VENTS**To work out the required number of whirlybirds/vents for your building, you will need to select a figure from the table "Exhaust Capacity CLS Ratings" to the left. For a commercial/industrial building we recommend 410mm,533mm and 610mm sized ventilators. Select a figure using the appropriate variables and the size of the ventilator you wish to use. **(*** Note: the bigger the vent, then the lesser the number of vents that will be required). *Using this figure and the figures gained from

**Step 1**and

**Step 2**, input them into the equation shown below.

**Number of Vents =**

**Volume (m3) x ACH (air changes p/hour)**

**divide**

**exhaust capacity (litres p/second) x 3.6**

Your answer should give you the amount of whirlybirds/roof vents your building needs, try this method a couple times to work out the most suitable sized ventilator for your building.