HEATING, VENTILATION & SERVICES 53 FANS OF EFFICIENCY
Mechanical extract fans are essential for home ventilation, yet often overlooked. Paul Williams of Domus Ventilation explores how choosing the right fan for a property – and ensuring proper installation – will aid effi ciency, performance, and regulatory compliance.
T
he humble mechanical extract fan is the unsung hero of the ventila- tion market. They’re never the star of a 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 frequently heavy with condensation.
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.
TYPES OF EXTRACT FANS There are two types of intermittent extract fans to choose from – axial and centrifugal – both of which are suitable for use in wet rooms, including bathrooms, toilets, kitchens, utility rooms and ensuites.
The simplest to install, axial fans are designed to work with short duct runs, typically no more than 1.5 metres, which connect directly to an external outlet or grille. Most kitchens and bathrooms with an external wall are suitable for axial fans. They incorporate impellers that force air to move parallel to the shaft around which the impellers rotate. Axial fans are the lower cost option.
Where longer duct runs are necessary, often because the room to be ventilated is in the centre of the house, centrifugal fans are the preferred option. These fans force air to move at right angles to the intake of the fan using centrifugal force. They produce more pressure to overcome resistance encountered in longer duct runs – normally up to a maximum run of 6 metres. Typically, they are quieter than axial fans, which in some instances may make them a better option – especially when it comes to ensuites – despite being more expensive. In addition to standard centrifugal and axial fans, there are also duct-mounted inline fans which come in both formats, as well as mied fl ow models which move air in both axial and radial direction relative
to the shaft and will develop higher air pressure but move less air than axial fans. ied fl ow fans are most frequently used in longer duct runs up to 6 metres. Inline fans are not installed within the room itself – frequently in the ceiling void 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: 100 mm and 150 mm. As you would expect, the larger fans are for larger bathrooms (typically greater than m, but would also be benefi cial 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 15 l/s. Ultimately, when choosing your fan, refer to the manufac- turer’s performance curve, which shows the relationship between the static pressure capabilities of a fan compared to its extraction rate, plus pressure loss in ducting, to determine the fi nal extraction rate.
GET IN CONTROL
Extract fans are available with different control options, so this is an area to also think about. We have done research into which are the most popular control options and they are at the opposite end of the market, fi nancially. 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 signifi cant change in humidity, are prevalent in higher end properties. PIR based controls that activate the fan on the detection of movement are also available, but are less popular.
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