PHAM NEWS | MARCH 2025 Ventilation & Heat Recovery 31


Ducting can make or break the system


Ducting is crucial for eff ective ventilation, impacting everything from large mechanical systems to simple bathroom fans. Paul Williams from Domus highlights the importance of ducting and off ers advice on product selection, best practices and installation tips for optimal airfl ow and compliance.


is the ideal time for installers to capitalise on this trend through projects in small housing development plots. The latest updates to Part F and Part L of the Building Regulations are designed to facilitate the transition to Net Zero including achieving nearly a third reduction in carbon emissions for new homes. Ducting can make or break


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a ventilation system, whether it’s a sophisticated mechanical ventilation with heat recovery (MVHR) system in a large house or a simple bathroom fan in an apartment. That’s because the ducting conveys the all- important fresh air to (and from, in the case of MVHR) the ventilation unit and into the property. If the air fl ow is impeded in the duct run, insuffi cient air reaches the fan in a timely way, and the property does not receive adequate ventilation. Maintaining air fl ow at a set level is especially important in whole house ventilation systems, as otherwise the systems will not perform to their best ability.


Wise choices I’d like to think that most people in this line of work invest time into researching whole house ventilation systems and, hopefully, into their choice of extract fans. But has similar time and eff ort been spent into researching ducting? Quite possibly not. As I have stated above, ducting is at the heart of a successful ventilation system, so it is important to take the time to ensure you choose duct systems wisely.


s MVHR increasingly becomes the preferred ventilation system for new build projects, now


 Schematic of the The HRXE-HERA range, which operates by continuously extracting moisture-laden air from wet rooms within the property while simultaneously drawing in fresh, fi ltered supply air from outside


 Ducting should be fi tted with insulation where it passes through unheated areas, such as loft spaces


There is no set standard for


Paul Williams Product manager at Domus Ventilation


ducting, but poor quality ducting is relatively easy to spot. If the ducting bows or looks like it’s concave, or the wall thickness appears uneven, avoid it as it will not provide a tight fi t when connected, leading to air and even condensation leakage. Good quality ducting will have exacting tolerances and connects together for minimal air and moisture loss and maximum system effi ciency. It will also come with ample accessories and useful products designed to assist you with site related constraints. Make sure the ducting has


been designed to work in harmony as part of a system and has been third party tested for end-to-end system performance. For MVHR and MEV system,


Getting the ducting right really is one of the most


important aspects of a residential ventilation system, yet it’s frequently the most


overlooked and undervalued


use quality rigid ducting in larger sizes. But whatever you do, and whatever size the ventilation system, avoid using fl exible ductwork in place of rigid ducting at all times, as it causes a lot more air resistance and can be crushed easily.


Drawing skills Many people misjudge the level of skill required to produce ducting drawings. The duct runs, the number of bends and the angle of those bends, plus the temperature of the areas the ducting runs through, all aff ect the air fl ow. It’s important to keep ductwork runs as short and straight as possible, and minimise the number of bends. This can best be achieved if you produce the drawing before the ventilation unit is specifi ed and before services, such as gas and water pipes, go in. Make full reference to dwelling and room ventilation rates within the drawing. By far the easiest option


though is to outsource the drawing. Most manufacturers, Domus Ventilation included, will provide a system drawing free of charge, along with duct take-off s and estimations. Lastly, be prepared! Site


related constraints may change, and the duct drawing may need to alter. If you have to make changes, recalculate the air fl ow rates and, where necessary, change product accordingly. For example, if you must include a bend where one didn’t exist before, consider using something like a Domus Greenline Bend which has been cleverly engineered to reduce duct bend resistance by up to 60%.


Stick to the plan Once your duct drawing is fi nalised and the ducting is ready to be installed, be sure to stick to it on site. Don’t try save time by making the duct runs simpler or swapping rigid ducting for fl exible ducting at fi nal connections or around obstructions. When it comes to installation


of extract fans, check if wall and in-room installation kits are


available as these will provide all the necessary parts to fi t the fan – including ducting and grilles – for a swift, straightforward installation. Be sure to fi t ducting


insulation and fi restopping products, as laid out in Building Regulations. Insulation is required where the ducting passes through unheated areas and voids, such as loft spaces. Firestopping products are necessary whenever a hole is made in a compartment wall for plastic ventilation ducting to pass through. In addition, non-combustible air bricks, such as Domus Ventilation’s Solis Air Brick, must be used where ductwork penetrates through the external cavity when above 18m in England and 11m in Scotland.


Taking time Getting the ducting right really is one of the most important aspects of a residential ventilation system, yet it’s frequently the most overlooked and undervalued. By taking the time to consider your ducting products, where they go and how they are installed, you are more than half way to ensuring a good ventilation system that is Building Regulations compliant. ◼ phamnews.co.uk/325/51


CUT TO THE CHASE


 MVHR is increasingly preferred for new builds, aligning with net zero goals


 Ducting is crucial for effective ventilation performance and airfl ow


 Choose high-quality ducting to prevent air and moisture leakage


 Accurate ducting drawings are essential for optimal air fl ow and effi ciency


 Follow installation guidelines to ensure system performance and compliance with Building Regulations


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