MVHR Ducting - Why it Really Matters

Installing a Mechanical Ventilation with Heat Recovery (MVHR) system in your home is an investment in your health, comfort and the quality of air in your home. When designed and installed correctly, it continuously supplies fresh, filtered air while recovering up to 95% of the heat that would otherwise be lost through other ventilation methods. 

However, to achieve these benefits, it’s essential that the ducting (the network of pipes that distributes the air) is designed and installed following best practice standards. Poor duct design or materials can reduce efficiency, increase energy use, and make your home less comfortable.

1. Use a Branch System Design

A 'Branch' ducting system is widely recognised as being the industry standard and is recommended by bodies such as the Building Research Establishment (BRE). 

This design features a main supply duct and extract duct running from the MVHR unit, with separate branches feeding each room. This layout ensures balanced airflow and optimal system performance.

2. Size Ducting Appropriately

Duct diameter determines how much air can move efficiently. Standard diameters include 125 mm, 150 mm, 200 mm, and 250 mm, depending on the required airflow rate (measured in L/s or m³/h).

As you branch off from the main duct, diameters reduce. For example, where the initial duct is servicing all valves it may have a 250mm diameter, which may then reduce to 150mm where it branches off to service a single valve.

In tight spaces (e.g. stud walls, ceiling voids), rectangular or “flat channel” ducting is sometimes used. But this should be limited and carefully designed to avoid excessive pressure drop.

3. Use Smooth, Rigid Ducting

The choice of duct material is critical. According to BRE guidance, smooth, rigid ducting (plastic or metal) provides the best airflow and energy efficiency.

Solid smooth flow ducting can offer the following benefits:

• Provides a higher heat efficiency
• Low-pressure loss resulting in low energy use
• Efficient low velocity producing less noise
• Resistant to crush damage
• Easily cleaned and maintained

Avoid flexible ducting where possible (especially in long runs), as its ridges increase pressure drop and reduce performance.

At BEAM, we only use precision-engineered smooth rigid ducting in both metal and high-quality plastic to achieve optimum performance and compliance with UK and Irish Building Regulations.

4. Insulate Ducts in Cold Spaces

Any duct passing through cold attics, lofts, or unheated voids must be fully insulated. This prevents condensation, reduces heat loss/gain, and helps maintain system efficiency. A minimum of 25mm aluminium foil backed wool insulation should be wrapped around the solid ducting. Putting loft insulation over the ducting is NOT efficient.

5. Seal All Joints Thoroughly

Air leakage undermines balanced systems. All ducting installed by BEAM's experienced installation team and partners is triple sealed at each joint (with glue, screws and tape) to ensure no loss of air. Leaky ducts not only reduce performance but may also bring in unfiltered air or moisture.

After installation, it’s essential that your MVHR system is commissioned and balanced by a qualified professional. This ensures that every room receives the correct airflow and that the system operates efficiently and quietly.

In fact, this is a requirement under:

• Northern Ireland: Building Regulations Part K

• Republic of Ireland: Building Regulations Part F

During commissioning, a technician will:

• Adjust fan speeds and room-by-room airflow rates

• Verify system pressure and noise levels

• Ensure compliance with design specifications

Whether you’re building a new home or retrofitting an existing one, BEAM’s experienced team and our approved network of distributor partners ensure every MVHR system delivers peak performance and energy efficiency.

We provide:

• Bespoke MVHR system design and duct layout plans

• Professional installation by certified engineers

• Testing, commissioning, and after-sales support

• Design and support for self-installation projects

Contact us today for expert advice or a free quote.