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You are here:- home > cooling index > fan index > cooling a small factory or workshop using fans

Cooling a small factory or workshop using fansroof extract fan

In the summer, high temperatures build up inside small workshops and factory units making them extremely unpleasant to work in. As a temporary measure portable fans are installed to provide relief for workers, however while portable fans cool small areas of the building, the rest remains stiflingly hot.

Roof extractor fans provide a simple, low cost method of cooling for small buildings or rooms of upto approximately 1400m3 (50,000 cubic feet).

Rate of air change for cooling

Roof extractor fans are normally used to provide 12 – 20 of air changes per hour for general ventilation, to provide fresh air and remove stale or contaminated air.

By increasing the air number of air changes to between 60 – 120 per hour, hot air is exhausted from the building and cooler outside air is sucked in though open doors and windows. As a result the temperature inside the building is held close to the outside temperature.

The rate of air changes per hour for cooling depends on the building construction and use:

Recommended air changes for cooling
Conditions Air changes per hour
Very warm workplace, offices, shops, etc. 60
Hot workplace, factory, workshop, warehouse, garage 80
Very hot workplace, bakeries, kitchens, laundries 120

Calculating fan sizes for cooling

Calculate the volume of the building or room:

Volume(m3) = length(m) x width(m) x height(m)

The extractor fan airflow per hour for cooling is:

Fan airflow (m3/hr) = building volume(m3) x air changes(changes/hour)

Where air changes for cooling is taken from above table.

Calculating opening sizes for supply air

The effectiveness of this type of cooling is dependant on the size and position of open loading bays, doors, windows, etc.

To calculate the area of open doors etc. required:

Convert the extractor fan airflow into m3/sec

Fan airflow(m3/s) = Airflow(m3.hr) x 0.00027

The minimum area of open doors etc. is:

Total area (m2) = Fan airflow(m3/s) x 0.3268

If the total area of open doors, windows, etc. is not big enough louvres or supply fans will need to be installed.


A small workshop measuring 10m x 15m x 3.5m is to be cooled using roof extraction fans. Calculate the size of extractor fan needed and minimum area of open doors, windows, etc.

Fan size

From above table 80 air changes per hour are required.

Volume of workshop = length x width x height = 10 x 15 x 3.5 = 525m3

Fan airflow = workshop volume x air changes = 525 x 80 = 42,000 m3/hr

Roof extractor fans with an airflow of 42,000 m3/hr are needed.

Open door, window area

Fan airflow = 42,000 x 0.00027 = 11.34 m3/sec

Total area of open doors etc. = 11.34 x 0.3268 = 3.7m2


Using roof extractor fans to cool buildings of upto 1400m3 has proved to be a very cost effective. By rapidly removing hot air from the building and sucking cooler air in through open doors and windows, the temperature inside can be kept close to the ambient (outdoor) temperature.

For larger factories and workshops over 1400m3 or where complicated air distribution problems exist a more sophisticated solution is necessary.

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