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Getting Ducting Right

Any ventilation system is reliant on the type of ducting used to ensure its effective running. Problems with ducting including the slumping of flexible ducting, the wrong type of joints and leaking ducts can lead to problems with the system’s performance. Up to 20% loss of efficiency can be accredited to kinks and other mechanical stresses. In 2013 the NHBC (National Housebuilding Council) also reported that poorly installed systems have a negative effect on indoor air quality and the effectiveness of MVHR systems.

Making sure you have selected and correctly installed the right type of ducting from the offset can help improve and prolong the efficiency of the system and can also help reduce any maintenance requirements in the long run.

When installing a MVHR system you should take into consideration the following:

Type of Ducting

Traditionally there are two types of ducting – flexible and rigid. While flexible ducting is cheaper, over time it has a tendency to slump resulting in the restriction of air flow through the system. due to condensation pooling. Rigid ducting is more expensive but it is cleaner and easier to seal resulting in better performance and reduced maintenance.

Flexible ducting has the higher risk of issues arising over time, so in all cases it is preferable to use rigid ducting where possible, unless there are difficult to reach places. Usually a combination of both flexible and rigid ducting is often used, with rigid ducting making up the main network and flexible ducting used as the branches.

There are also airtight and semi-rigid ductwork systems coming onto the market which give the best of both worlds. This ductwork is extremely lightweight as it is manufactured from plastic and achieves airtightness Class C (EN12237). These new generation of ductwork systems are easy and quick to install. They offer the benefits of rigid ductwork with the ease of installation due to the semi-flexible pipework.


A duct that is too small will result in issues with noise and high resistance so sizing is also an important factor to consider. Reputable manufacturers should be able to advise on the correct size of ducting for a given system.


It is recognised that an issue with ductwork can be its sealing. The use of duct tape for sealing and making connections is highly advised against. The use of tape and mastic makes it difficult to obtain an air tight seal and their adhesive properties can also start to break down over time creating leaks. Rigid airtight connections which provide a consistent air tight seal work better for the long term.

To ensure a more effective ventilation system it is essential to ensure you install the right ductwork. This in turn will result in a more efficient ventilation system and long term performance.

If you would like to know more about how Robinsons can help you with your ventilation system requirements, please contact us to discuss further.

Source: Don’t take chances with ducting (PHAM News Magazine June 2016)

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