A client complaining about MVHR noise is not just voicing an impression, there is a figure behind it. Approved Document F advises that the average A-weighted sound pressure level of a ventilator running under normal conditions, and not at boost rates, should not exceed 30 dB LAeq,T in noise-sensitive rooms such as bedrooms and living rooms when a continuous system runs at its minimum low rate, nor 45 dB LAeq,T in less noise-sensitive rooms such as kitchens and bathrooms. Two consequences for the diagnosis. The level is read at the low rate, not on boost. And what the guidance frames is the noise in the room, not the noise of the machine, so a unit that looks faultless on its datasheet can still miss these levels once installed.
Identify the source of the noise on your MVHR unit before stepping in
Telling a normal noise from an abnormal one (humming, vibration, whistling)
An MVHR unit often makes a light, steady hum, especially on high speed. The noise becomes suspect if it appears suddenly, varies between rooms, or comes with vibrations, rattling, or a high-pitched whistle. Also check whether the sound gets louder when a door closes. That can reveal an imbalance in the flow rates.
Locating the source: unit, ducts, vents, mounting and partitions
Start near the unit. Put your hand on the casing. A clear vibration often points to a mounting or fixing issue. Then follow the ducts. A crushed, poorly tensioned duct, or one touching the roof structure, can amplify the noise. On the vents side, whistling often comes from an air passage that's too narrow, a clogged vent, or one that's poorly adjusted.
Checking the general condition: dirt build-up, mechanical play, tightness and power supply
Cut the power then check for dirt build-up and the condition of the air inlets and fan. Mechanical play (bearing, impeller) or loose screws can make the whole unit vibrate. Also check the power supply and connections. Unstable voltage or a worn capacitor can make the motor work harder. If in doubt, call in a professional. To go further on maintenance and the checks to plan, see our article on MVHR maintenance.
Reduce noise through basic maintenance and settings
Cleaning vents, air inlets and the unit casing to limit turbulence
When an MVHR unit gets dirty, the air is forced through, and the noise rises. Dust off the vents and air inlets, then vacuum the casing and accessible grilles. Gentle cleaning, without soaking the parts, is often enough to restore a steadier flow and a quieter operation.
Adjusting flow rates and limiting over-ventilation: speed, humidity-controlled settings, balancing
Over-ventilation makes vents whistle, especially in small rooms. Check the selected speed, the state of the humidity-controlled settings, and the balancing between rooms. The goal is to get back to the planned nominal flow rate, without a permanent "boost", while keeping good air quality (see also the regulatory ventilation flow rates).
Checking dampers and accessories to avoid whistling and backdraughts
A stuck damper, a poorly fitted connector, or an unsuitable accessory can create continuous whistling. Check the vent dampers, the couplings, and any backdraught dampers. Refit parts, replace worn seals, and secure the backdraught damper to prevent air from flowing back.
Improve the acoustics of the ductwork: solutions on ducts and connections
Replacing or reworking the ducts: suitable flexible ducting, diameter, elbows and airtightness
A noisy MVHR unit often comes from ductwork that's under too much strain. Restore the right diameter along the whole run. Limit tight elbows and crushed sections, especially on flexible ducting. Take care with the connections using couplings and sealing tape to avoid whistling and air leaks (see also duct network sizing).
Approved Document F is just as explicit on the ductwork itself. Rigid ducts wherever possible, flexible ductwork kept to final connections and to a maximum of 1.5 m, pulled taut so the full internal diameter is maintained. It also asks that each air terminal keep a free area of at least 90 % of the free area of its duct, which is precisely the restriction that turns into a whistle.
Adding a sound trap or MVHR silencer: where to fit it and how to size it
Fit a sound trap as close as possible to the casing, before the first branch, and if needed also on the most sensitive vents. Choose a model of the same diameter, with enough length to attenuate high frequencies. Check the pressure loss to keep a correct flow rate.
Treating structure-borne noise: flexible couplings, anti-vibration clips and decoupling
Vibrations travel through the mounts. Insert a flexible coupling between the casing and the ducts. Use anti-vibration clips and avoid direct contact with the roof structure or partitions. A small amount of decoupling is often worth more than a "more powerful" unit.
Limit vibrations from the casing: mounts, location and sound insulation
Fitting the casing on anti-vibration mounts and removing rigid contact points
An MVHR casing quickly transmits its vibrations to the structure. Fit it on anti-vibration mounts (pads, rubber bushings) or suspend it with dedicated fixings. Avoid screwing it directly into a joist or a slab. On the ducts side, plan for flexible couplings and leave a small amount of play. The goal is simple: zero rigid contact between the casing, the ducts and the plasterboard.
Choosing the right location: loft, plant room, suspended ceiling and accessibility
Location often accounts for half the quietness. In a loft, install on a stable support, away from bedrooms. In a plant room, you gain in comfort and easy access. In a suspended ceiling, watch the weight and vibrations on a lightweight frame. Always keep access to the filters, tap-off points, condensate drain and power supply.
Boosting sound insulation around the casing without hurting maintenance
To reduce airborne noise, build a small enclosure with mineral wool and cladding, without compressing the materials or blocking the motor's ventilation. Plan for a removable cover or access hatches. The insulation should stay clean, dry and inspectable. Otherwise you gain decibels but lose ease of maintenance.
Replacing the MVHR unit: choosing a quieter, compliant model in 2026
Comparing noise levels: dB(A), sound pressure, spectrum and measurement points
For a quieter MVHR unit, compare the dB(A) level and, above all, the measurement point. One manufacturer may quote a level at the casing, another at the vent. Check the sound pressure, the spectrum (low frequencies are perceived more strongly) and the test conditions. In a renovation, aim for a casing fitted on rubber mounts and vents suited to the sleeping areas.
Selecting the right technology: single-flow, humidity-controlled, heat-recovery and uses
Self-regulating single-flow units are robust, but not always the most comfortable. Humidity-controlled units adjust flow rates according to moisture levels, which is useful in occupied housing. Heat-recovery units make sense if you're also addressing airtightness and insulation, since they recover heat. The right choice depends on the volumes involved, the existing ductwork and access to the loft.
Securing the job in 2026: compliance, certification, funding and good installation practice
In 2026, secure compliance for flow rates, air inlets and roof or façade outlets against Approved Document F. On funding, heat-recovery units travel inside an ECO4 package for an eligible household, as the ventilation that has to accompany a tighter envelope. In practice, take care over duct airtightness, balancing, and plan for easy filter access for maintenance. The fan unit, the ducting and the acoustic accessories are then priced in the same survey as the room-by-room flow rates.
