DOMESTIC VENTILATION SOLUTIONS
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Avoiding the pitfalls with
I
t is almost two years since the introduction of the updates to Approved Document F and there has been a drive towards increasing the energy efficiency of ventilation systems, part of which involves ensuring that these systems are correctly installed. Accredited courses and competent persons schemes, such as those provided through the NICEIC, have become the recognised standard for ventilation and many installers have undergone training to educate on the importance of adequate ventilation and the importance of the correct specification and installation. However, there are still a number of potential pitfalls with ventilation installation and the most common issues relate to the installation. With MVHR systems, leakage of air from ductwork connections, excessive flexible duct, duct not insulated when required, means systems are unlikely able to deliver the required airflow and may cause damage to the fabric of the building and leading poor indoor air quality. High quality ducting and good installation is
therefore essential to the effective running of a ventilation system and there are a number of factors to take into account.
When ducting is selected and installed correctly, it
can improve and prolong the efficiency of the whole system, leading to long term low maintenance. On the other hand, a ventilation system that has issues with the ducting, which can range from ‘slump’ of flexible types, through to inadequate jointing mechanisms, is always going to underperform.
Semi-rigid ducting has many benefits
Choice of ducting has proven to be very important and many installers prefer semi rigid ducting as it is quicker to install and offers a click and connect seal when compared to rigid ducting which requires sealing and a mechanical fix. It also offers lower maintenance and improved performance of the ventilation system.
Rigid ducting is often used as part of a trunk and
branch system which involves a length of ducting from the unit with bends and t-pieces acting as off- shoots. This requires multiple joints and sealing and fixing. These are generally via screws and mastic or glue. Flexible ducting is also used as part of the offshoots or to marry up tighter areas, such as in a loft space. This type of ducting should only be used for final connections and should not be in excess of 200mm when used. This is due to the inherent nature of the ducting being prone to ‘slump’ if used in larger lengths when unsupported and also higher levels of resistance due to the ridges and ease of manipulation. This ducting has been found squashed under loft insulation, or not appropriately cut, which
then prevents the ventilation unit from being able to do its job. The lack of support and fragile nature of flexible ducting can lead to pooling of condensation in the section affected, restricting the flow of air through the system.
Leakage
Another potential issue is leaking ducts and these can occur for a variety of reasons, such as kinks or other mechanical stresses It can result in over 20 per cent loss of efficiency of a ventilation system. Air leakage in ductwork can also cause moisture damage within the building fabric. Leaks can also be a common issue in flexible ducting due to poor connections, vermin attack, coming into contact with sharp objects, wear on abrasive surfaces in the loft space or damage during installation.
Ductwork sizing
Issues can arise with the installation of ventilation systems if the duct is too small for the airflow rate, which results in high resistance and noise issues. Our ventilation specialists are able to advise on the optimum size of ducting for a given system. Correct commissioning of the system is also crucial to ensure that the correct airflow is delivered and that the system is properly balanced.
ventilation design
Mark Isles, sales director at EnviroVent, looks at avoiding the pitfalls with ventilation system installation, in order to ensure energy efficiency and long-term performance
28 April 2024
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