How to choose the correct fan:
Effective ventilation, conforming to the building regulations, depends on the selection of a fan or fans of the correct size and capacity.
To do this, you need only consider -

• The cubic capacity of the area to be ventilated
• The required number of air changes per hour

Multiplying the cubic capacity by the number of air changes determines the optimum fan capacity required.

	Example 1	Example 2
Room	Toilet	Shower Room
Volume	1.5 x 1.2 x 2.5 = 4.5 cubic metres	2 x 2.5 x 2.5 = 12.5 cubic metres
Number of air changes	6	15
Performance	4.5 x 6 = 27 cubic metres/hour	12.5 x 15 = 187.5 cubic metres/hour
Installation	Through wall or window	Through loft space using over 2m of ducting
Fan required	4800 (100mm axial) = 85 cubic metres/hour	4806 (100mm centrifugal or in-line) = 225 cubic metres/hour

Axial Fans
Are designed to move air over short distances i.e. through walls or windows.
They are not suitable for ducting lengths over 2 metres.

Centrifugal Fans
Are designed to move air over longer distances and perform well against the resistance of longer ducting lengths.

Fans used with ducting
If fans are used with ducting, it is important to remember that long lengths of ducting will reduce the fan's performance.
As a rule, when long lengths of ducting are required, centrifugal fans need to be selected.

Close Window