With little thought given to ventilation in homes throughout most of the twentieth century, ventilation ducting was mostly confined to use with cooker hoods. Consequently, there was little ducting product choice and not much skill required (although, even then, the wrong size ducting was frequently used, resulting in excessive – and unnecessary – noise!).
All that changed in 2010 when Building Regulations Part F was introduced, specifically addressing ventilation in dwellings for the first time. Several revisions later, the most recent in 2022, Part F has helped spawn an entire ventilation industry, with a slew of innovative products, including whole house ventilation systems, and advances in ducting.
While much attention is understandably paid to ventilation products such as MVHR and MEV, ducting is frequently overlooked. Yet whole house ventilation systems require extensive ducting, and that ducting needs to be correctly specified, drawn, and installed. Get it wrong and you may well end up with a system that doesn’t deliver the air flow required, is noisy, can be prone to condensation both inside or outside of ductwork and, ultimately, may not get signed off by Building Control. To avoid these scenarios, here are four principles to follow that are at the heart of all good ventilation systems.
Invest in quality ducting
My first point here is, unless absolutely necessary, to avoid using flexible ductwork in place of rigid ducting as it causes a lot more air resistance and can be crushed easily.
While there is no quality standard when it comes to ducting, it’s actually quite easy to tell the difference between poor and good quality, which will also be reflected in the price (yes, like most things in life, you get what you pay for!).
Poor quality ducting often bows or looks like it is concave, or the wall thickness appears uneven. This is a problem because these systems are designed to push fit, so if the tolerances are too wide, a snug fit cannot be obtained which will result in air and even condensation leakage. Good quality ducting will have exacting tolerances and push fits together for minimal air and moisture loss and maximum system efficiency.
Ducting that has been designed to work in harmony as part of a system and has been third party-tested for end-to-end system performance is the ultimate choice, and is especially important when installing whole house ventilation systems where the air flow needs to be maintained at a set level if the MEV or MVHR system is to perform to its best ability.
A quality ducting system will also come with a range of useful products and accessories to help you meet site circumstances, such as the Domus Greenline Bend which reduces duct bend resistance by up to 60%.
Ducting drawings: start early
Designing a whole house mechanical ventilation system, especially an MVHR, requires a level of skill. While the location of the air handling unit is normally straightforward, the duct runs, the number of bends and the angle of those bends, plus the temperature of the areas the ducting runs through, all affect the air flow.
The key to a successful ducting system design is firstly to ensure the drawing is done prior to unit specification and prior to other services, such as gas and water pipes, going in. Then, keep ductwork runs as short and straight as possible, and minimise the number of bends. Make full reference to dwelling and room ventilation rates.
Ducting drawings are not easy, so why not hand this aspect over to the ducting manufacturer. Most manufacturers, Domus Ventilation included, will provide a system drawing free of charge, along with duct take-offs and estimations. We also provide on-going support, so if you do run into any unforeseen difficulty we can advise accordingly.
Of course, once you have a design, stick to it on site! Don’t be tempted to cut corners, making the duct runs simpler or swapping rigid ducting for flexible ducting at final connections or around obstructions.
Use appropriate insulation
Ducting insulation is required under Building Regulations where the ducting passes through unheated areas and voids, such as loft spaces. It reduces the possibility of condensation forming, which can lead to mould and unsightly stains. If fitting an MVHR system, then the intake and exhaust to atmosphere should also be insulated, regardless of whether it is in a cold area or not.
The minimum duct insulation standard is the equivalent of at least 25mm of a material having a thermal conductivity of ≤0.04W/(m.K). Standard building insulation materials are mostly unsuitable, but even domestic duct insulation products on the market are often unable to meet this requirement; our own Domus Thermal exceeds it.
Stay compliant: fire safety
When a hole is made in a compartment wall for plastic ventilation ducting to pass through, the hole must be firestopped to restore the walls’ fire rating in accordance with Approved Document B of the UK Building Regulations. It is essential that the firestopping product you use for this has been specifically designed for this purpose.
Document B also requires ductwork penetrating through the external cavity including termination to be non-combustible when above 18m in England and 11m in Scotland. This means using air bricks made from non-combustible metal must be used above these heights, such as the Domus Ventilation Solis Air Brick range. Made from 1.5mm galvanized steel (fire class A1) non-combustible material, Solis Air Bricks are fully compliant with Building Regulations and suitable for use with all external wall types.
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