Many manufacturers claim that their fan can do certain things. However, when the fan is installed, these claims may not be possible. For example, many manufacturers will claim that their fan is the quietest out there. Whilst the fan may be able to operate at this sound level when on a test bench in a sound room with no ducting, it may not be able to ventilate according to Building Regulations on the speed this sound level was tested on.

When selecting the fan for your installation, you will need to consider the performance you will get from the fan when you’ve installed it. A rough way of finding out the relative installed performance of fans is to look at the fan curve for the product. This graph shows the flow rate in l/s against the static pressure in Pa. Static pressure is the driving force of the fan and is what dictates the length of ducting can be installed for a relative performance.

An indicative way of using a performance graph is to take a line up to the flow line from the flow rate you want. For this example, we shall be using the QuietAir 100 performance graph. To ventilate a bathroom to Building Regulations, you need to extract 15 l/s. Simply find 15 l/s on the X-axis and follow the line-up until you reach the flow line. Once you reach the flow line, go at a right-angle towards the Pa. This example of the QuietAir can do 17.5 Pa on its low speed at 15 l/s.

It is important to remember that the higher the Pa the more ducting a fan can do at that performance. If the Pa is below 10 for a 15 l/sec then this is not recommended due to it not being able to meet the Domestic Ventilation Compliance Guides installation recommendations of 1.5m and 2 90 degree bends of flexible ducting with a 90% free air grille. Please note this is a guide only and you will need to have an accurate system pressure reading to ensure you buy the right fan for your needs.

All of this data is available for Airflow fans on our website but with other manufacturers you may have to ask for this data. Airflow offers a tool called Selectair which conveniently gives you the fans that will meet your application needs based on the performance that you need and the amount of ducting you are using.

You don’t want to install a shoddy fan, as this will in turn look bad on you. This is why Airflow ensures that their claims that we put on our fans are based on their installed performance. We believe in being transparent as possible with you so that you can be as informed as possible when making your choice of ventilation product. The most accurate way to find out the performance of the fan that you have installed in your ventilation system is through a powered flow meter complete with a hood. This is the recommended way to measure a system based on the NICEIC Approved Ventilation Installer Scheme