David Treharne, Senior Engineer at Domus Ventilation, explains the different extract fans available to ensure you select the right one for the job.
Intermittent extract fans are a cost-effective, easy to install, simple to operate method of bathroom and kitchen ventilation. They provide rapid local extraction, either under occupant or automatic control, and help to reduce condensation and mould in the process.
There are essentially two types of intermittent extract fans – Axial and Centrifugal – each designed to perform best under well-defined situations.
Axial fans
The 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.
Centrifugal fans
For longer duct runs, Centrifugal fans are the preferred option. They produce more pressure to overcome resistance encountered in longer duct runs – normally up to a maximum run of 6m. Typically, they’re quieter than Axial fans, but also more expensive.
Inline 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 (most frequently used in longer duct runs up to 6m).
Unlike standard fans, Inline fans aren’t installed within the room itself, but slightly removed. The actual fan could be located in the ceiling void or attic, connected to the room via ducting mounted with a decorative grille at the end. There’s also the option to incorporate a ceiling light within the grille. Due to their discreet location they’re ideal for installation in showers. More often than not they’re sold in installer-friendly kits containing all the parts you’ll require.
Inline fans have a number of benefits over their standard counterparts. Firstly, because the fan can be mounted anywhere in the attic, it’s not limited by the installation space. Secondly, noise from the fan operation is minimised by being located away from the exhaust point on the ceiling (insulating the ductwork will also help). Thirdly, they can work out to be highly cost-effective in a large room as it’s possible to create multiple exhaust points in the ceiling whilst using just the single fan.
Clearly, Inline fans involve extra installation work and are often best-suited to new builds and major refurbishment projects.
So you’ve armed yourself with the information you need to make an informed decision on the type of fan to fit, but how do you then decide between the different brands on offer?
I suggest focussing your decision-making on the following key factors:
Energy-efficiency
Check that your fan meets Building Regulations Part L, which requires Specific Fan Power (SFP) to be no higher than 0.5W per litre per second (W/l/s). There are fans in the market that operate at lower energy consumption rates, such as Domus Ventilation’s Sapphire fans which have an SFP down to just 0.19W/(l/s). In addition, check the fan’s energy consumption in standby mode as some use an extra 10-20% of the overall power consumed when in standby.
Available accessories/control options
The range of compatible fan accessories is important as it provides you with greater flexibility and choice. Virtually all manufacturers offer an automatic shutter to prevent backdraught but less provide a good range of control options. There are the straightforward timer and pull cord options through to more advanced humidity control options that are capable of identifying and reacting to a significant change in humidity, plus PIR based controls that activate the fan on the detection of movement. An override facility should be considered, maybe in the form of an overrun timer, most often set to deactivate the fan at a set time after the light has been switched off.
Noise and aesthetics
That brings us to noise and appearance. A fan that operates down to 32dB(A) is a quiet fan, but also ensure you fit quality ducting as poorly manufactured, incorrectly fitted ducting can rattle. The fan will be visible so you want it to look good. Therefore select models that either compliment the surrounding decor or that are discrete and unobtrusive. Domus Ventilation, for example, has designed its 100mm Axial range with interchangeable fascias to suit customer tastes and decor.
For more information about the range of fans available from Domus Ventilation visit: www.domusventilation.co.uk
