A Self-Builder's Guide to MVHR Design and Installation

A Self-Builder's Guide to MVHR Design and Installation

A Self-Builder's Guide to MVHR Design and Installation: 10 Principles You Need to Know

1.  What is MVHR and Why You Need It

Mechanical Ventilation with Heat Recovery (MVHR) is a system that ventilates your home whilst recovering heat from outgoing air. It helps maintain indoor air quality, reduces energy bills and prevents issues like dampness and mould. For self-builders focused on energy efficiency and comfort, MVHR is essential, especially in airtight, well-insulated homes.

Also, ventilation is mandatory when undertaking a new house build or major refurbishment, as it is covered under Building Regulations - Approved Document F. The aim of Part F is to certify that adequate air quality is maintained via the removal of stale air and its replacement with fresh air to prevent issues like condensation and mould.  Find out further information here

2.  The Importance of Early Planning

If considering MVHR, it is essential that it is planned from the outset along with other essential services like electrics and plumbing. MVHR is a whole house system that is part of the fabric of the building and extends to all living and ‘wet’ rooms in the home.

Early planning will avoid costly changes and allow you to choose optimal routes for ductwork, valve locations and the MVHR unit.

3.  Balancing Airflows is Crucial

MVHR systems are designed to move air through the house expelling pollutants and bringing in fresh air. The system supplies fresh air to living spaces (like bedrooms and living rooms) and extracts stale air from moisture-producing areas (like kitchens, toilets and bathrooms).

The system should be designed so that both supply and extract air flows are equal, ensuring the system is balanced. This balance is critical for maintaining comfortable indoor temperatures and air quality.

4.  Sizing the MVHR System

    Your MVHR system must be appropriately sized for the volume of air in your home. Too small and it won’t effectively ventilate - it will be inefficient and likely to be noisy – too large and increased energy consumption, increased space requirement and operational costs can occur. The principle behind getting a system design produced is to ensure this doesn’t happen.

    When selecting an MVHR system, it's crucial to match the unit's capacity to the actual ventilation needs of the building, considering factors like room size, occupancy and building regulations for ventilation rates. Having a full system design produced will ensure the right size unit for optimal performance and efficiency

    5.  Designing for Low Noise Levels

      If improperly designed, MVHR units may become noisy. To minimise noise:

        • Position the MVHR unit in a soundproofed area (like a utility room).
        • Install acoustic silencers between the MVHR unit and living spaces.
        • Use quality components and an MVHR unit which has a proven low noise rating
        • Use the specified duct sizes and install using minimal bends
        • Ensure the ducts are secured and well supported to prevent sagging
        • Locate the unit away from noise sensitive areas such as bedrooms
        • Use a radial duct system to minimise sound transmission issues

      6.  Ducting Design: Short, Straight, and Insulated

        The layout and design of your ducting are essential for the system’s efficiency. Keep duct runs as short and straight as possible to reduce resistance and pressure drops. Insulate ducts that pass through unheated spaces to prevent heat loss and condensation. Flexible ducting should be avoided as it increases resistance and harbours dust build up. All of the above will be reviewed during system design and followed during installation.

        7.  Placement and Selection of Valves and Grilles

          For any MVHR system to work effectively, the placement, sizing, and type of valves are essential. Using the correct valves will ensure that the supply air is optimized for comfort, health, and energy efficiency.

          Cheap valves not only look ugly but their ability to control airflow and how that air is distributed across the room is compromised. This is also part of producing a good design as air velocity from any valve should be controlled to ensure the system does not produce draughts. Many modern valves control air paths by spiralling air across the room rather than down vertically to avoid this issue

          Noise can also occur more easily with low-cost valves and poorly designed systems due to air velocity.

          Make sure there’s enough distance between supply and extract vents to avoid short-circuiting (where fresh air is immediately extracted before circulating).

          8.  Ensuring an Airtight Home

            When considering installing an MVHR system, making the house airtight is crucial. To achieve what can be considered airtight and for MVHR systems to be optimally beneficial, an airtightness level of at least 5m³/(h.m²) @ 50Pa. This is because MVHR relies on controlled air paths to supply and extract air from the home.

            Without air tightness, the MVHR system is less effective which ultimately results in more heat loss and negates some of the benefits of having an MVHR system.

            By extracting air from moisture-prone areas like kitchens and bathrooms, MVHR helps in managing indoor humidity levels. An airtight envelope aids in directing this moisture-laden air to the extraction points rather than allowing it to spread or escape through leaks and reduced air leakage means less risk of condensation on cold surfaces, which in turn decreases the likelihood of mould growth.

            So, an airtight house is beneficial for MVHR, but it's crucial to maintain adequate ventilation to ensure healthy indoor air quality consequently, MVHR should be part of a well-thought-out strategy for both air tightness and ventilation.

            9.  System Controls

            Once installed and commissioned, most units can be left alone to run without manual intervention. Most have automatic humidity functions. These detect rises in humidity and boost the flow rates in response. They also have summer bypass for when the outdoor temperature might be higher than the indoor temperature. At this point recovering heat to further warm the incoming air is counterproductive. Summer bypass allows the system to stop the heat recovery process, preventing the MVHR from adding heat to the home when it's already warm.

            Apart from the above, which are generally standard features of modern MVHR units, there are a further host of controls giving filter alerts, running mode indicators, manual boost controls and wi-fi enabled controls.

            See here for a copy of Zehnder control option catalogue

            10.  Ask the Experts

              MVHR design and installation require careful attention to detail, from planning ductwork routes to ensuring the system is quiet, efficient, and easy to maintain. As a self-builder, understanding these key factors will help you install a system that delivers long-term energy savings and a healthy, comfortable living environment. If you have further questions you’d like to ask us our contact details are below.

               

               

              If you'd like to find out more about how an MVHR system operates, why not check out one of our other blogs:  The Anatomy of an MVHR System

              Epicair Ltd is a leading designer and installer of MVHR systems in the UK.  Please give us a call on 01892 600121 or contact us on mvhr@epicair.co.uk to talk to our experts who will be happy to answer your questions on your MVHR project.