Understanding MVHR Ducting for Better Home Ventilation
Understanding MVHR Ducting for Better Home Ventilation
Choosing the right MVHR ducting is just as important as choosing the MVHR unit itself. A good ducting layout helps air move efficiently around the property, reduces noise, supports heat recovery performance and makes the system easier to commission.
Whether you are working on a new build, renovation or home ventilation upgrade, understanding the basics of MVHR ducting can help you choose the right components for your project.
What is MVHR ducting?
MVHR ducting is the network of pipes and fittings that connects your MVHR unit to the rooms in your property and to the outside air terminals.
The system usually has two main jobs:
Fresh air is supplied to living spaces such as bedrooms, lounges and dining rooms.
Stale, moist air is extracted from wet rooms such as bathrooms, kitchens, utility rooms and en-suites.
As the air passes through the MVHR unit, heat is recovered from the outgoing stale air and transferred to the incoming fresh air. This helps improve indoor air quality while reducing heat loss.
Types of MVHR ducting systems
There are two main types of ducting commonly used with MVHR systems: rigid ducting and semi-rigid radial ducting.
Rigid ducting
Rigid ducting, sometimes called a branch or leg-and-branch system, uses larger duct runs with fittings such as bends, tees, reducers and connectors to distribute air around the property.
This type of system can work well when it is carefully designed and installed with good quality components. It is often used where straight duct runs are possible and where there is enough space to route larger ducting through ceilings, lofts, walls or service voids.
Rigid ducting is available in different materials, including PVC and metal ducting, and in a range of sizes depending on the airflow requirements of the system.
Semi-rigid radial ducting
Semi-rigid radial ducting uses individual duct runs from a manifold to each room. Instead of sharing one main duct route with multiple branches, each room has its own dedicated duct run.
This can make radial ducting easier to balance and commission, especially in domestic MVHR systems. It also reduces the number of joints hidden within the building fabric, which can help lower the risk of air leakage if the system is installed correctly.
Semi-rigid ducting is commonly available in 75mm and 90mm sizes and is often supplied in coils, making it easier to route through joists, ceiling voids and awkward spaces.
What size MVHR ducting do I need?
The correct duct size depends on the MVHR unit, the airflow rates required, the duct layout and the available space within the property.
The duct connections on the MVHR unit are usually larger than the ducting used for individual room runs. Common MVHR unit port sizes include 125mm, 150mm, 160mm and 180mm, although this varies by model.
For radial ducting systems, 75mm and 90mm ducting are commonly used for individual supply and extract runs. Larger rooms or higher airflow requirements may need multiple duct runs.
Undersized ducting can restrict airflow, increase pressure in the system and make the MVHR unit work harder. Oversized ducting can be more expensive and harder to install. The aim is to choose ducting that allows the required airflow without creating unnecessary resistance or noise.
Why duct layout matters
A well-planned duct layout can make a big difference to the performance of an MVHR system.
Good MVHR ducting design should aim to:
Keep duct runs as short and direct as possible.
Reduce unnecessary bends and sharp turns.
Avoid crushed or restricted ducting.
Use the correct size ducting for the required airflow.
Keep access in mind for future maintenance.
Limit air leakage by using suitable connectors and seals.
Poor duct design can reduce system efficiency, increase noise and make commissioning more difficult. For this reason, duct routes should be planned before installation begins, especially on new builds and larger renovation projects.
Does MVHR ducting need to be insulated?
Some MVHR ducting needs to be insulated, especially where ducts pass through cold areas such as lofts, garages or unheated voids.
The main intake and exhaust ducts between the MVHR unit and the outside should usually be insulated to help reduce heat loss and condensation risk. This is particularly important when warm indoor air or cold outdoor air passes through unheated spaces.
Ducting that runs inside the heated part of the home does not always require insulation, but the project design should always be checked. If the system is being used alongside cooling or summer comfort features, insulation may be needed on more duct runs to help prevent condensation.
Insulated ducting is larger than standard ducting, so this should be considered early when planning duct routes.
How can MVHR ducting affect noise?
MVHR systems are designed to run continuously, so noise control is an important part of the design.
Noise problems are often caused by poor duct layout, excessive bends, undersized ducting, high fan speeds or unsuitable component choices. If the ductwork creates too much resistance, the MVHR unit may need to work harder to achieve the required airflow, which can increase noise.
To help reduce noise, consider:
Correctly sized ducting.
Smooth, direct duct routes.
Suitable silencers or attenuators.
Good quality manifolds and air valves.
Correct commissioning once installed.
A properly designed and balanced MVHR system should provide continuous ventilation without becoming disruptive in everyday use.
Installation and commissioning
MVHR ducting should be installed carefully so that airflow is not restricted. Joints should be secure, ducts should not be crushed, and any bends should be kept as smooth as possible.
Once the system is installed, commissioning is essential. This is the process of measuring and adjusting the airflow to each room so the system performs as intended.
Commissioning helps ensure that the correct amount of air is supplied and extracted throughout the property. It also helps confirm that the MVHR unit is working efficiently and that the system has been installed in line with the design.
Rigid ducting vs semi-rigid ducting: which is best?
The best option depends on the property, the installation space and the system design.
Rigid ducting can be a good choice where there is enough room for larger duct runs and where the route can be kept simple. It is strong, widely available and suitable for many MVHR installations.
Semi-rigid radial ducting is often preferred for modern domestic MVHR systems because it can be easier to route through the property and allows individual duct runs to each room. This can make balancing and commissioning more straightforward.
In many cases, a system may use a combination of ducting types. For example, larger insulated ducting may be used between the MVHR unit and outside terminals, while semi-rigid radial ducting may be used for internal room connections.
Choosing quality MVHR ducting components
MVHR ducting is usually hidden within the building, so it is worth choosing reliable components from the start.
Important components can include:
Semi-rigid ducting.
Rigid PVC or metal ducting.
Insulated ducting.
Manifolds.
Air valves.
External grilles and terminals.
Duct connectors and seals.
Silencers and attenuators.
Fixings and support brackets.
Using suitable ducting and accessories can help reduce air leakage, improve system performance and make the installation more reliable long term.
Final thoughts
MVHR ducting plays a major role in how well your ventilation system performs. The right ducting system should support good airflow, low noise levels, efficient heat recovery and reliable long-term performance.
Before ordering your MVHR ducting, consider the type of system you are installing, the size of the property, the duct routes available and the airflow requirements for each room.
At Ventilation Superstore, you can find a wide range of MVHR ducting, semi-rigid ducting, rigid ducting, insulated ducting, manifolds, air valves, fixings and ventilation accessories to help complete your project.
Shop MVHR ducting and ventilation products online at ventilation-superstore.com.
