By Ruth MacEachern
Product Manager
As every installer should know, high quality ducting is essential to the effective running of a ventilation system and there are a number of important considerations 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. Poorly installed duct work can potentially damage the ventilation unit and the fabric of the building. Indeed, an NHBC (National Housebuilding Council) report from 2013 demonstrated how poorly installed systems have a negative effect on indoor air quality and the effectiveness of MVHR systems.
In order to avoid these pitfalls, we've put together a checklist of factors that need to be taken into account when choosing a ducting system whilst adhering to the domestic ventilation compliance guide:
Ducting can be made of rigid materials or from flexible components - many buildings use a combination of types to suit different purposes. Although rigid ducting costs more, it results in reduced maintenance and improved performance of the ventilation system. Many installers also prefer it because it is easier to seal and clean. Frequently, installers will choose rigid ducting for the main trunk and more flexible ducting for offshoots. However, flexible ducting should be used as a last resort, as it poses the greater risk of issues developing later on. In some spaces, flexible ductwork can be the only choice, for example, when reaching vents in difficult places, such as corners or house eaves. However, it is always preferable to use rigid ducting because the flexible variety is prone to ‘slump’ over time. This can lead to pooling of condensation in the section affected, which restricts the flow of air through the system.
Problems with ducting can arise immediately after installation or in years to come, should ducts become broken or torn. Another consideration is leaking ducts, and these can occur for a variety of reason, such as kinks or other mechanical stresses, which can lead up to 20 per cent loss of efficiency of a ventilation system. Issues with ductwork can result in insufficient air flow as a result of a slump in flexible ducting. This can be tested by putting your hand over an intake vent to see if you detect air movement. In this situation, there is likely to be a breach or kink in the duct. Air leakage in ductwork can also cause moisture damage within the building fabric.
The sizing of the duct is also important. A duct that is too small for the airflow rate will result in high resistance and noise issues. A reputable manufacturer should be able to advise on the optimum size 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.
With systems like Mechanical Ventilation with Heat Recovery (MVHR), ductwork is vital to its efficiency and to ensure good indoor air quality in the home. Remember to check in the domestic ventilation compliance guide.
HM Domestic Ventilation Compliance Guide 2.0 (NHBC Standards) states that all duct connections require sealing. Guidance says that where ducts are installed against a solid structure, this can be difficult to achieve – in such locations, pre-assembly of duct sections should be considered. It also states that joints in ductwork, and between ductwork and other system components, should be securely fixed and sealed with purpose-designed connections, in accordance with manufacturers’ recommendations. In addition, it requires that all joints should be durable and airtight.
Problems arise with ductwork when it results in high pressure drop. This is mainly caused by unsealed connections and this can cause high air leakage, the end result of which is increased energy consumption and noise, due to the units having to work harder to provide adequate ventilation.
Because of the issues that the industry faces and how this impacts on the effectiveness of ventilation systems, we recently introduced two new ductwork systems – airtight and semi-rigid. These types of purpose-designed ventilation ductwork can be installed very quickly and easily, making it immediately airtight. A major benefit of the semi rigid option is that it provides the benefits of rigid but with the ease of installation offered by semi-flexible piping.
Obviously rigid ductwork is not suitable for every possible situation, which is why we also introduced the semi-rigid range. This ductwork is available in various circular and semi-circular dimensions. All ductwork can be connected to one universal distribution box by use of adapters. This eliminates the need to keep stock of numerous box types and limits costs. This semi-rigid duct work is manufactured from plastic, so is extremely lightweight. It achieves airtightness Class C (EN12237) and has an adaptor to step mass flow. This type of ductwork offers post installation access to restrictors, which is ideal for maintenance.
NHBC guidance recognises that sealing can be an issue with ductwork and it strongly advises against the use of duct tape to achieve connection and sealing. Use of mastic and tape makes it difficult to achieve a consistent quality air tight seal and it can lose its adhesive properties over time and start to leak. Our alternative is rigid airtight mechanical connections which are quick and easy to install and provide a consistent quality air tight seal for the long term.
Getting the ductwork right can be the key to more effective ventilation systems and use of the new generation of ductwork is also quicker and more straightforward to install. With whole house systems like MVHR, it is essential to install the correct ductwork, with the end result being a more efficient ventilation system and guaranteed installed performance for the long term, whilst adhering to the domestic ventilation compliance guide.
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