In a correctly designed and commissioned system, MVHR noise in occupied spaces is usually comparable to background office noise, often in the 20 to 35 dB(A) range for internal rooms. In many cases, users only notice a gentle airflow sound when the system runs at boost speed or when something has been installed incorrectly.
For trade professionals, the real question is not “are MVHR systems noisy” but “what makes them noisy in practice and how do we avoid it on site”. Noise usually comes from fan units, air velocity in ductwork, and poorly isolated fixings rather than the technology itself.
How Loud Are MVHR Units In dB Terms?
Manufacturers typically quote sound power or sound pressure levels at specific airflows and external resistances. For occupied spaces, guidance such as CIBSE and Building Regulations performance criteria often aim for noise levels of around 25 to 35 dB(A) in bedrooms and offices, and slightly higher in circulation spaces and WCs.
Modern centralised MVHR units from established brands often achieve very low casing radiated noise when correctly mounted and attenuated. Single room heat recovery units will be more noticeable at higher speeds, but many still fall comfortably within acceptable limits for commercial and multi residential schemes when correctly specified.
What Causes MVHR Noise In Real Projects?
Most noise issues trace back to high air velocities, undersized or poorly routed ductwork, and incorrect terminal selection. If air is forced through tight bends, flexible ducting or small grilles at high speed, turbulence increases and so does perceived noise at the grille.
Structure borne vibration is another common culprit. When MVHR units are fixed directly to lightweight partitions, vibration can pass into the building fabric and radiate as low frequency hum or drone in adjacent rooms.
How Does Design Affect MVHR Noise Levels?
Noise performance starts at the design stage. Correct ventilation rates, sensible duct velocities, and realistic external resistance assumptions will keep fan speeds down and reduce both breakout and regenerated noise.
Specifying smooth rigid ductwork wherever possible and minimising sharp bends helps maintain laminar airflow and reduce turbulence. Correct sizing and placement of supply and extract terminals also spreads airflow across the diffuser, which reduces whistling or rushing sounds at grilles.
Take a look at our in-depth guide on MVHR system design which covers best practices to follow.
How Important is Product Selection?
Choosing the right MVHR unit makes a significant difference to perceived noise on a project. High quality MVHR units with efficient EC motors, balanced impellers and good acoustic insulation can deliver the required airflows at lower fan speeds and lower noise.
eFans stocks a full range of heat recovery and MVHR units from Vent Axia, Zehnder, Elta and S&P, ranging from single room units to large whole building systems with heat recovery efficiency up to 93 percent and airflow from 32 m³/h to 900 m³/h.
This breadth gives contractors flexibility to match unit performance to the acoustic expectations of offices, schools, healthcare buildings and multi residential blocks.
How Does Installation Quality Change Perceived Noise?
Even the quietest MVHR unit can seem noisy if it is installed without attention to detail. Common on site issues include kinks in flexible ducting, poorly fitted silencers, uninsulated ducts passing through acoustic partitions, and terminals placed too close to the occupied zone.
Simple measures can resolve many complaints. Examples include re-routing flexible duct runs, adding or repositioning attenuators, fitting anti vibration mounts, and balancing the system so that boost airflow is only used when required.
Do Single Room MVHR Units Create More Noise Than Central Systems?
Single room heat recovery units are installed directly through the wall, so the fan is closer to the occupied space. At higher speeds this can make them more noticeable than a central unit hidden in a plant room or ceiling void, particularly in small offices or hotel rooms.
However, up to trickle speed many modern single room units remain relatively quiet and are often masked by normal building background noise.
For noise sensitive applications, looking at low specific fan power figures, EC motors and published dB(A) data at realistic duty points will help you compare options from Vent Axia, Zehnder, Elta and S&P.
How Does MVHR Noise Link to Energy Performance and Costs?
Noise and energy performance are closely connected because both relate to fan speed and system resistance. If ductwork is inefficient, fans must work harder, which increases both sound levels and running costs.
How to Minimise MVHR Noise On Site
There are several practical steps you can take to reduce the risk of noise complaints.
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Keep duct velocities within recommended limits for supply and extract branches
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Use rigid duct where possible and keep flexible duct to short, straight connections
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Mount MVHR units on anti vibration pads away from lightweight partitions
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Include appropriate silencers on both supply and extract sides
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Commission systems carefully so that boost speeds are only used when needed
When value engineering, it is worth considering the long term cost of call backs and remedial work. Spending a little more on high quality low noise MVHR units from brands stocked by eFans can offset those risks.
How Can MVHR Noise Be Managed In Existing Buildings?
Refurbishment and retrofit schemes often present the toughest acoustic challenges because duct routes and plant locations are constrained. In these cases, careful survey work, realistic airflow targets and early collaboration with acoustic consultants can prevent problems later.
Sometimes the best option is to replace older, noisier fans with modern, efficient MVHR units that offer better acoustic and energy performance. Take a look at our list of the best MVHR systems that can help specifiers pick replacements that suit both the building layout and the client’s acoustic expectations.
Frequently Asked Questions
How can I tell if an MVHR system is too noisy?
An MVHR system may be too noisy if speech in a normal tone is difficult within a metre of a supply or extract grille, or if low frequency hum is clearly audible in quiet rooms such as bedrooms or offices. Measuring dB(A) levels and comparing them with project acoustic criteria or guidance such as CIBSE limits provides an objective check.
Do MVHR boost modes always increase noise significantly?
Boost modes raise fan speed to meet higher ventilation demand, so some increase in noise is normal. If the system has been designed with reasonable duct velocities and adequate attenuation, the boost noise should still sit within acceptable limits for the space type.
Can duct silencers really make a big difference to MVHR noise?
Yes, correctly selected duct silencers on supply and extract branches can significantly reduce fan and airflow noise reaching occupied spaces. Their performance depends on length, internal lining, and correct placement relative to bends and terminals, so they should be specified as part of the overall acoustic strategy.
Are plastic ducts quieter than metal ducts for MVHR systems?
Both plastic and metal ductwork can perform well acoustically if sized and installed properly. What matters more is duct diameter, layout, joint quality and the use of lined sections or attenuators where required, rather than the material alone.
Do MVHR filters affect system noise levels?
Dirty or clogged filters increase system resistance, forcing fans to run faster to maintain airflow and potentially increasing noise. Regular filter maintenance and using the correct replacement filters keeps resistance down, which helps maintain both low noise levels and energy efficiency.