A ventilation system can pass an airflow check and still be unpleasant in a bedroom. If the fan, ductwork or terminals are intrusive at the setting used every night, occupants may turn the system down, switch it off or open a window. The measured flow rate then tells only part of the story.
The 2026 guidance treats noise as part of ventilation performance
Approved Document F, Volume 1: Dwellings was updated in 2026 for future building work in England. It says mechanical ventilation should be designed and installed to minimise noise, including through correct duct sizing and jointing, secure or resilient mounting where structure-borne sound may be a problem, and appropriate equipment selection.
The document also says a fan should be sized so that normal background ventilation does not require it to run near maximum capacity. That is a useful design principle: the everyday operating point matters, not merely the largest airflow shown on a product sheet.
Airflow and acoustic comfort are separate checks
Commissioning confirms whether the required air is moving through the system. It does not automatically establish whether the resulting sound is acceptable in a particular room. Fan sound can travel through the air, along ducts, through terminals or into the building structure before re-radiating elsewhere.
A fan that has to work against excessive resistance may also become more noticeable. Long routes, avoidable bends, undersized ducts, compressed flexible ductwork and restrictive terminals can all increase system pressure. The 2026 guidance therefore connects duct layout, sizing and installation with successful operation.
A bedroom is not a utility room
The guidance notes that good acoustic conditions would be supported by an average ventilator level no greater than 30 dB LAeq,T in noise-sensitive rooms at the minimum low rate, and 45 dB LAeq,T in less sensitive rooms at the relevant higher or intermittent rate. It also makes clear that noise testing is not itself required by this guidance.
Those figures should not be detached from their operating conditions. A measurement at boost rate does not answer the same question as a measurement at the background setting used during sleep. Equally, an overall A-weighted level may not fully describe tonal sound, cycling, rattles or sudden speed changes that attract attention.
The quietest system is not simply the quietest fan
Product data matters, but the completed installation includes the fan, casing, supports, ducts, bends, branches, attenuators, terminals and room. A quiet unit connected to a poor route may not create a quiet room. A well-installed system can also deteriorate if filters are not maintained or components become loose.
This is why diagnosis should consider both airborne and structure-borne paths. Changing the fan may be appropriate, but it should not be the automatic first answer when the dominant issue is a duct restriction, vibration bridge or terminal close to a bed.
What I would check
For a new design, I would examine the required airflow at each mode, the proposed pressure duty and the acoustic data at the actual operating point. For an existing installation, I would first establish which mode is running, whether the airflow is correct and how the sound reaches the room.
- Confirm the normal, boost and automatic control settings.
- Measure airflow before assuming that quieter operation means adequate ventilation.
- Listen for tonal, fluctuating and structure-borne components as well as overall level.
- Inspect duct sizes, bends, flexible sections, supports and terminals.
- Check maintenance condition and whether filters or grilles are obstructed.
- Assess external noise before relying on open windows for purge ventilation.