Centrifugal Fan

With an axial fan, the air is pushed through the fan and moves parallel with the vent. Most domestic wall fans use an axial impellar and are ideal for bathrooms, toilets and smaller rooms where the moving air is to be ducted directly through the wall or installed in a windowpane.

Axial fans are not capable of pushing air through particularly lengthy vents. They are not capable to push air for more than 5 metres becuase they cannot manage the inherent air pressure involved with long or twisting ducting runs. If you choose an axial fan, try to ensure that the ducting is as direct as viable. If you are not able to use an axial fan due to the distance or complexity of the pipe work, a centrifugal fan should be used.

Centrifugal fans extract air at right angles to the intake of the fan, and whirl the air outwards to the outlet by deflection and centrifugal pressure. The air enters the fan where the shaft is and is moved from the vent to the fan shell when the impeller rotates.

If you find your installation will run longer than 5 metres, you will need to use a centrifugal fan to power it. Indeed, such is their efficiency that there is some centrifugal fans, that can be used in a duct run up to 50m!

Centrifugal fans can be split into a duo of different types, you can purchase either a wall mounted fan or an inline duct fan. Visually, a stock wall mounted type will look roughly identical to a wall mounted axial fan. When shopping for a fan, because of the similar appearance between the two, it could be problematic to tell the difference between the two, you will normally find it will be stated on the packaging.

If your lavatory or kitchen doesn't have an outside wall, you most likely need to use a wall mounted centrifugal fan. In these rooms, there is no other forms of ventilation such as windows; to extract the air properly, a fan is definately necessary and wall mounted fans suit this situation. The most common trouble is when air is not being extracted correctly is when an axial fan is installed in this type of room. An axial fan is just not capable of extracing air in this way.

An inline fan is not placed at the air entry point but at a appropriate location down the piping. They therefore look wholly different from wall fans but most importantly are not installed in the room from which they are extracting air. Typically, ducting will be run from a roof mounted vent to an exterior wall vent and the fan will be placed in an appropriate place in the duct. An inline fan is ideal for both big kitchens and bathrooms where a lot of air needs to be extracted.