2nd August 2022

We are often asked how noisy our MVHR units are — in order to answer this question, we need to explain what are the causes of noise in ventilation systems. It is important to look at a complete MVHR system, not just the MVHR unit. Good duct design and specification play a huge part in the operating efficiency and noise levels of an MVHR system. Higher specification units have constant volume fans (as opposed to constant speed fans) which operate by constantly assessing the system pressure and adjusting the fan to maintain the commissioned airflow. A poorly designed duct network adds to the system pressure and in turn prompts the unit to run at a higher speed in order to maintain flow, thus making it noisier and increasing energy usage.

A well-designed system, on the other hand, allows the MVHR fans to run at the lowest speed necessary to maintain the desired airflow, resulting in quiet, low-energy systems. It is important to size the duct appropriately, relatively large volumes of air are being moved through the system, and using a larger duct may be used to keep in-duct air velocities lower. Forcing too much air down a small duct means high velocities and increased noise.

Unnecessary bends, sharp bends, and corrugated ducting also result in increased duct pressures in the MVHR system, which, in turn, increases the noise from the unit and the turbulent airflow. If a branched ducting system is not designed correctly with appropriately placed attenuation, sound can be transferred between rooms – this is known as cross-talk.

A correctly specified radial ducting system with a smooth inner core and manifold for air distribution air reduces system pressure and prevents cross-talk issues. It is also important that the unit be maintained. Filters must be cleaned regularly as dirty filters will result in increased resistance to airflow. This causes fans to run faster, which again will lead to increased unit noise. Finally it is important to choose an appropriately sized unit for the property; an undersized unit will have to work harder to provide adequate airflow.