VIEWPOINT
EXTRACT FANS: THE UNSUNG HEROES
Paul Williams, product manager at Domus Ventilation
THE HUMBLE MECHANICAL Extract fan: the unsung hero of the ventilation market. They’re never the star of a company’s product portfolio and, once they’re installed, they are mostly forgotten or ignored. Yet these compact mechanical devices keep millions of our homes and facilities well ventilated year after year, removing stale air that’s often heavy with condensation. But frequently fans are purchased and fitted without the due consideration they deserve. Here we explain the types of extract fans and where they are suitable for use to ensure your customers get the job done right the first time.
Types of extract fans There are two types of intermittent extract fans - axial and centrifugal – both of which are suitable for use in wet rooms, including bathrooms, toilets, kitchens, utility rooms and ensuites.
The lower cost option and simplest to install, axial fans are designed to work with short duct runs, typically no more than 1.5m, which connect directly to an external outlet or grille. Most kitchens and bathrooms with an external wall are suitable for axial fans.
Where longer duct runs (up to a maximum of 6m) are necessary, centrifugal fans are the preferred option as they produce more pressure to overcome resistance encountered in longer duct runs. Typically, they are quieter than axial fans.
In addition to standard centrifugal and axial fans, there are also duct-mounted inline fans which come in both formats, as well as mixed flow models. Inline fans are not installed within the room itself – frequently in the ceiling void
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or attic – but are connected to the room via ducting mounted with a decorative grille at the end. This makes them ideal for installation in splash zones. As installation of inline fans requires longer ducting, they are mostly used in new builds and major refurbishment projects.
Selecting the right fan Extract fans may be the most basic type of domestic mechanical ventilation, but they still need full consideration when choosing which is right for a particular application.
Domestic extract fans come in two sizes: 100mm and 150mm. As you would expect, the larger fans are for larger bathrooms (typically greater than 9m²), but would also be beneficial in heavy usage bathrooms and those where there is no natural ventilation.
As well as size, the fan’s performance needs to be taken into account. Measured in litres per second (l/s) or metres cubed per hour (m3/hr), the air extraction rate is vital. To meet Building Regulations, the minimum extraction rate for a bathroom extractor fan is 15l/s. Domus Ventilation fans are all Building Regulations compliant, with extract volumes up to 48.8l/s for axial fans.
Get in control
Extract fans are available with different control options. We have done research into which are the most popular control options and they are at the opposite end of the market financially. The basic timer and pull cord model remains popular as a cost-effective option, whilst the more advanced fans with humidistat or combined humidistat & timer that react to a significant change in humidity,
Top Left: Spotvent Inline fan Top right: Curzon centrifugal fan Above: Axial Fans
are prevalent in higher end properties. Our new intermittent axial fan range - the DBF100 100mm fan and the DKF150 150mm fan - are available in with these different control options. PIR based controls that activate the fan on the detection of movement are also available, but are less popular.
Common mistakes The biggest error we see when it comes to extract fans is not the fan directly, but the ducting, which can make or break any ventilation system. Advise customers to use rigid ducting,
not flexible duct work which causes more air resistance and can be easily damaged. It’s also a good upsell opportunity. Query a customer buying different size ducting from the size of the fan. If the fan has 150mm diameter spigot, 150mm ducting needs to be used.
Humble though they may be when compared to whole house ventilation systems, choosing the right extract fan is essential if the fan is to perform to the desired standard and to meet Building Regulations Part F Ventilation. Helping your customer choose wisely takes little time, but should have a positive impact on the indoor air quality of the property in which they are fitted. BMJ
www.buildersmerchantsjournal.net January 2025
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