Differences Between Extractor Fans

These days when you put in a new bathroom, toilet, utility room or kitchen, building regulations say that you need to install an extractor fan. But what type of extractor fan should you buy from the thousands on offer?

There are 3 main “families” of fans to choose from: axial, centrifugal and inline fans. Axial fans are the most common type of extractor fan that you see. They are ideally suited to being placed on a wall and ducted straight outside. This means you cut a hole in a wall, fit the fan, and the air goes straight out the back and outside. Axial fans are therefore best suited to installation on walls.

Centrifugal fans are generally used where you need to duct the fan over long distances, often up to 50 metres. They work by turning the air through a 90° bend within the fan itself, which increases the air pressure and thus the power of the fan. As a result, centrifugal fans are normally more powerful than axial fans, but also noisier. As well as being capable of being ducted over longer distances, they can also cope with bends in the ducting. Centrifugal fans are suited to installation on walls and ceilings.

Inline fans can be either axial or centrifugal, but are not installed on walls or ceilings, but in the void or loft space above a ceiling. In general they are centrifugal. They are nearly always more powerful than wall or ceiling fans, and again are very good at ducting over long distances and duct runs with bends.

Some fans can be installed in windows, but you generally need to buy a window kit specific to that fan, and there aren’t many that are made, so make sure before you buy that the fan can be installed in a window! Window fans are becoming less and less common…as all glass is now double glazed, cutting a hole in the glass is a harder job than it used to be, and once the hole is cut, it needs to be sealed very carefully or condensation will get between the panes.

Also, make sure you get the correct size and extraction rate for the room you are renovating. For toilets the minimum rate required is 6 litres a second, for bathrooms it’s 15 litres a second, for utility rooms it’s 30, and for kitchens it’s 60, unless it is adjacent to the hob, in which case it’s 30.

As a rough guide, all bathroom and toilet fans are 4 inch, whereas utility and kitchen fans are 6 inch.

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