Mechanical ventilation with heat recovery (MVHR) systems must meet strict acoustic standards to ensure comfort and compliance. The UK’s Approved Document F (ADF) sets baseline requirements for noise control, while Passivhaus standards go further to support ultra-low energy buildings.

To help you understand the decibel targets below, 25dB(A) is somewhere between rustling leaves and a whisper, 35dB(A) is somewhere between a whisper and a refrigerator, and 45dB(A) is somewhere between a refrigerator and moderate rain. So, if your system is louder than rainfall there’s something wrong with it.

ADF Requirements (UK Building Regulations):

• Bedrooms and Living Rooms: MVHR systems must not exceed 30dB LAeq,T when running at minimum rate.
• Kitchens and Bathrooms: Up to 45dB LAeq,T is permitted when systems operate at boost or intermittently.
• Part O (Overheating): ‘Thermal Purge’ ventilation must not exceed 30dB LAeq,T ±5dB in habitable rooms.

Passivhaus Requirements:

• Bedrooms and Living Rooms: Maximum 25dB(A) system noise.
• Wet Rooms and Kitchens: Maximum 30dB(A).
• Plant Room or Adjacent Areas: Maximum 35dB(A).

These tighter Passivhaus thresholds reflect the need for quiet, continuous ventilation in highly insulated, airtight buildings—where background noise is minimal and any mechanical sound is more noticeable. All internal and external doors and windows must be closed during commissioning and sound testing. Heat pumps and plumbing systems, if active, can skew results and should be accounted for.

Early acoustic planning is vital to avoid costly rework and ensure compliance with both regulatory and comfort standards. MVHR units should comfortably meet daily ventilation demands using no more than 50% of their maximum fan capacity—rather than being undersized to save money and then pushed beyond efficient operation. Fan units must be mechanically isolated from rigid ducting fixed to the building structure, using anti-vibration mounts to prevent walls and floors from resonating. Ductwork should be carefully designed to minimise turbulence, which increases pressure, motor noise, and energy use. Exterior terminals must also be properly sized to maintain airflow and prevent noises at the façade.

If the design needs to change because of site specific conditions, for example if the plumber puts the cylinder where the MVHR was supposed to go, or the electrician does the same with the consumer unit, the MVHR design should be updated to reflect the new positioning. The system pressure should then be recalculated to ensure the change does not compromise energy or acoustic performance. Fail to do this and you jeopardise the warranty.

You should feel the benefit of MVHR without needing to hear the benefit.

If you already have an MVHR system that started loud then magically became quiet after a quick engineers visit, or if it started quiet but you’re experiencing condensation or damp, the most likely explanation is that someone turned it down below the correct level to solve or avoid a noise issue.

In the trade we call this ‘cut & paste’ commissioning. People get away with it because home owners, project managers, and building control officers don’t carry calibrated anemometers. Instead they rely on the integrity of ‘competent people’. You can normally tell if the commissioning only took an hour or two rather than a day or two, or if the ‘measured’ air flow rates on your commissioning certificate match EXACTLY with those on your design.

If in doubt hire an anemometer or pay for independent verification.