Noise Silencers

Silence – the most important indicator of a ventilation system

Why do heat recovery units make noise?

Even the quietest units generate sound. Fan rotation and airflow movement through ducts create vibrations and aerodynamic noise. Without proper insulation, this sound travels through metal pipes like a telephone wire – straight into your bedroom or living room.

Constant background hum is exhausting. Although you might not notice it during the day, at night even 30 dB(A) noise (equivalent to a whisper) can disturb deep sleep. A common mistake is investing in an expensive unit but skimping on silencers, which forces you to run the system only at minimum speed later.

How do acoustic silencers work?

A silencer acts like a sound sponge. Inside, mineral wool covered with perforated metal or fabric absorbs sound waves while allowing air to flow freely. The result – fresh air enters the rooms, but the noise stays trapped inside the silencer.

A properly designed system is almost silent. By using rigid or flexible silencers, you can reach a level where you only know the ventilation is on by checking the control panel.

Reduces noise by up to 25 dB(A) – this means your ventilation system will run quieter than a running fridge or a library.

How to choose the right noise silencer?

The most important rule: length matters. The longer the silencer and the thicker its insulation layer, the more effectively it absorbs sound. Never choose the shortest option if you have space for a longer one.

• Flexible silencers – ideal for tricky spots where you need to make a turn or connect a manifold. They are lightweight, cheaper, and act as vibration dampers.
• Rigid silencers – robust galvanized steel elements installed in main trunk lines. They are durable and offer lower air resistance.
• Insulation thickness (25 mm vs 50 mm) – 50 mm insulation better dampens low frequencies (fan thumping), while 25 mm handles mid and high frequencies (airflow whistling) perfectly.

Which model should you choose?

A combined solution is usually best. We recommend using rigid silencers on main lines immediately after the heat recovery unit, and flexible ones just before manifolds or diffuser boxes. This ensures maximum effect across different frequency ranges.

Installation tips for maximum silence

Strategic locations in the system

One silencer is often not enough. To achieve high-class comfort, you need to dampen noise in several stages.

1. At the unit – strictly install silencers on both supply and extract ducts. This protects the entire duct system from vibration transmission.
2. Before bedrooms – if the main duct is long, noise can regenerate due to turbulence. An additional smaller silencer right before the bedroom grille guarantees dead silence.
3. Bends – a flexible silencer installed at a bend works more effectively than a straight one, because sound waves hit the insulation material directly.

Operation

Noise silencers are long-lasting and maintenance-free. The most important thing during installation is not to damage the inner layer and, if using flexible models, not to compress them too much. Correctly installed silencers will last as long as the duct system itself, without changing their properties for decades.