Mechanical ventilation with heat recovery (MVHR) is a whole-building or single-room ventilation system that extracts stale, humid air and replaces it with fresh filtered air, recovering up to 93% of the heat in the process.
It keeps buildings well ventilated without the energy losses associated with traditional extract fans or opening windows.
For contractors and facilities managers specifying ventilation in new builds or retrofits, understanding how MVHR works, and where its limitations lie, is essential before making a recommendation.
What Is a MVHR System?
A Mechanical Ventilation with Heat Recovery system uses a central heat exchanger to transfer warmth from outgoing stale air to incoming fresh air, without the two airstreams mixing. A network of supply and extract ducts connects the unit to wet rooms, kitchens, and living spaces across the building.
The heat exchanger sits at the core of every MVHR unit. Warm, stale air from bathrooms and kitchens passes through one side of the exchanger, while cold fresh air from outside passes through the other. The two airstreams run close together, allowing heat to transfer across a thin membrane without any cross-contamination of the air itself.
Modern units achieve heat recovery efficiencies between 75% and 93%, meaning a very high proportion of the energy that would otherwise be lost is retained and used to pre-warm the incoming supply air. This directly reduces the heating load on the building.
Key Components of an MVHR System
-
Supply and extract ductwork connecting all habitable rooms and wet rooms
-
A central MVHR unit housing the heat exchanger and twin fans
-
Filters on both the supply and extract airstreams (typically G4 and F7 classes)
-
Summer bypass functionality to prevent overheating during warmer months
-
Heat recovery controllers for demand-controlled ventilation and boost settings
What Are the Different Types of MVHR Systems?
MVHR systems broadly split into two categories: whole house systems and single room units. Choosing between them depends on building type, project scope, budget, and whether the building is a new build or a retrofit.
Whole House MVHR Systems
Whole house MVHR systems serve an entire property through a centralised unit and a duct network. They are the gold standard for new build residential projects and commercial buildings targeting high airtightness standards, including Passivhaus certification. A single unit manages ventilation for every room, making control and maintenance straightforward.
eFans stocks a full range of whole house MVHR systems from Vent-Axia, Zehnder, Elta and S&P, with airflow rates ranging from 100 m³/h up to 900 m³/h to suit everything from small dwellings to large commercial premises.
Single Room Heat Recovery Units
Single room units recover heat from one space at a time, typically a bathroom, kitchen, or utility room. They are far simpler to install than a ducted whole house system and represent a practical option for retrofit projects where running ductwork throughout an existing building is not feasible.
eFans carries single room heat recovery units in through-the-wall, wall, ceiling, and floor-mounted configurations, with airflow rates starting from 32 m³/h. These units suit contractors working on apartment refurbishments, extensions, or room-by-room upgrades.
What Airtightness Level Should MVHR Be Specified?
MVHR is generally recommended for buildings with an air permeability of 5 m³/(h.m²) at 50 Pa or lower, tested in accordance with ATTMA TS1. Below this threshold, uncontrolled air infiltration is sufficiently reduced that the MVHR system can properly govern ventilation rates and recover heat effectively. Above this level, draughts bypass the system and the energy saving case weakens considerably.
Passivhaus projects target air permeability below 0.6 ACH at 50 Pa, at which point MVHR is essentially non-negotiable for adequate ventilation. For standard new build dwellings, which typically achieve between 3 and 7 m³/(h.m²), airtightness improvements carried out alongside MVHR installation will have a direct and measurable impact on how well the system performs in practice.
What Are the Advantages of MVHR Systems?
Significant Energy Savings
MVHR systems recover heat that would otherwise be expelled to the atmosphere. In a well-sealed building, this can meaningfully reduce space heating demand. Units with recovery efficiencies at or above 90% make a measurable contribution to Part L compliance and support targets under SAP calculations for new dwellings.
Improved Indoor Air Quality
Unlike passive or trickle vents, MVHR continuously filters and renews the internal air supply. Incoming air passes through filters that remove particulates, pollen, and pollutants before it enters occupied spaces. This is particularly valuable in urban locations where outdoor air quality is poor, and for buildings where occupants have respiratory conditions.
Moisture and Condensation Control
Persistent humidity is a major cause of mould growth, structural damage, and health complaints in buildings. MVHR extracts moisture-laden air from kitchens and bathrooms at source and replaces it with drier, filtered supply air, keeping relative humidity levels within a comfortable and structurally safe range throughout the building.
Quieter Operation Than Traditional Extract Fans
Because MVHR units operate continuously at low speeds rather than intermittently at high speeds, occupants notice far less fan noise during normal use. This is an advantage in residential settings and particularly in bedrooms, where noise from conventional extract fans can be disruptive.
Supports Compliance With Building Regulations
Approved Document F of the Building Regulations requires adequate ventilation in all new dwellings and many commercial buildings. MVHR satisfies the requirements of System 4 whole building mechanical ventilation as defined in the document, making it a compliant and increasingly specified solution for new builds.
What Are the Disadvantages of MVHR Systems?
Higher Upfront Cost Than Basic Ventilation
The capital cost of a whole house MVHR system, including the unit, ductwork, commissioning, and controls, is substantially higher than a simple extract fan setup. For retrofit projects in particular, the cost of installing ductwork through an existing building can make the economics challenging without careful project planning.
Requires a Well-Sealed Building to Perform Efficiently
MVHR only performs as intended in buildings with low air permeability. In a leaky building, uncontrolled air infiltration bypasses the heat exchanger entirely, meaning the energy saving benefit is largely lost. For retrofit projects, draught-proofing work often needs to accompany MVHR installation, adding to project cost and complexity.
Ductwork Design and Installation Demands Skill
Poor duct design leads to pressure imbalances, noise, reduced airflow, and inefficient operation. Installers need to understand duct sizing, routing, balancing, and acoustic attenuation. Systems that are not properly commissioned rarely deliver their rated performance and can create complaints from building occupants.
Filters Require Regular Maintenance
MVHR filters need replacing typically every six to twelve months depending on the environment and unit specification. Neglected filters restrict airflow, reduce heat recovery efficiency, and can allow contaminants to pass into the supply air. Facilities managers and building owners need to factor ongoing maintenance into their total cost of ownership.
Summer Bypass Needed to Avoid Overheating
During warmer months, recovering heat from outgoing air and adding it to incoming air can cause internal temperatures to rise uncomfortably. Most quality MVHR units include a summer bypass mode that routes incoming air around the heat exchanger, but this adds complexity and is a feature specifiers should confirm is included before selecting a unit.
How Do Building Regulations Apply to MVHR Systems?
Approved Document F sets out the ventilation requirements for new and materially altered buildings in England. It defines four ventilation systems, and MVHR falls under System 4, the highest specification whole building mechanical ventilation approach.
Compliance requires the system to deliver defined minimum airflow rates to each room type and to be correctly commissioned and tested before handover.
Approved Document L, which covers energy efficiency, recognises heat recovery ventilation as a means of reducing a building's carbon emissions and improving its energy rating under SAP assessments.
Specifying MVHR can therefore contribute to compliance on two fronts simultaneously, making it an increasingly attractive option for developers working to meet current Building Regulations.
Why MVHR System Design Matters
A well-specified unit fitted to a poorly designed duct layout will underperform regardless of its rated efficiency. Pressure drops caused by oversized duct runs, too many bends, or undersized spigots all reduce airflow and put strain on the fans.
Getting the design right from the outset protects both the performance of the system and the reputation of the installer.
Commissioning is equally important. A system that has not been balanced correctly will deliver too much air to some rooms and too little to others, creating draught complaints and uneven air quality.
For contractors and M&E engineers, investing in proper design and commissioning support at the start of a project is far less costly than returning to site to rectify problems after handover.
For projects operating at a larger scale, design complexity increases further. Our guide to commercial MVHR systems covers the additional considerations around capacity, controls integration, and compliance that apply when specifying for commercial buildings.
Choosing the Right MVHR Unit for Your Project
Selecting the right system starts with calculating the required airflow rate for the building and identifying whether a centralised whole house approach or individual room units are more appropriate for the project type.
From there, unit efficiency, noise ratings (measured in dB(A)), filter class, controls compatibility, and available space for installation all factor into the final specification.
eFans stocks a comprehensive range of heat recovery and MVHR units from leading manufacturers including Vent-Axia, Zehnder, Elta and S&P, covering airflow rates from 32 m³/h to 900 m³/h and heat recovery efficiencies up to 93%.
The range includes units suitable for single bathrooms through to large commercial premises, with ceiling, wall, through-wall, and floor-mounted form factors available.
For projects requiring boost control, humidity sensing, or integration with building management systems, eFans also supplies a full range of heat recovery controllers compatible with the units it stocks
If you are still weighing up your options, our MVHR buying guide walks through each of these considerations in detail to help you specify with confidence before you order.
Frequently Asked Questions
What is the difference between MVHR and MEV?
MVHR (Mechanical Ventilation with Heat Recovery) supplies fresh air to the building and extracts stale air, recovering heat in the process. MEV (Mechanical Extract Ventilation) only extracts air from wet rooms and relies on background ventilators to admit fresh air.
MVHR recovers heat and provides filtered supply air throughout the building, making it more energy efficient and better for indoor air quality than MEV.
Does MVHR work in retrofit projects?
MVHR can be installed in retrofit projects but it works best in buildings that have been made reasonably airtight. In older buildings with high air permeability, the efficiency gains are reduced because uncontrolled draughts bypass the heat exchanger.
Single room heat recovery units are often a more practical retrofit solution than a full centralised system, as they require no ductwork beyond a single core drill through the wall.
What maintenance does an MVHR system require?
MVHR systems require filter replacement every six to twelve months, an annual inspection of the heat exchanger core, and periodic cleaning of the supply and extract valves. Some units also have a summer bypass damper that should be checked annually.
Facilities managers should include MVHR maintenance in planned preventative maintenance schedules to maintain efficiency and air quality performance.
What airflow rate do I need for an MVHR system?
Airflow rate is calculated based on the number of rooms, floor area, occupancy, and the requirements of Approved Document F. A typical three-bedroom dwelling requires a whole house MVHR unit with a minimum airflow rate of around 100 to 150 m³/h.
Larger properties and commercial buildings require higher capacity units. A ventilation design calculation should always be carried out before specifying a unit.
Can MVHR help meet Part F and Part L Building Regulations?
Yes. MVHR satisfies the requirements of System 4 mechanical ventilation as defined in Approved Document F and contributes to reduced carbon emissions as recognised in SAP energy assessments under Part L.
For new residential builds and commercial projects targeting improved energy performance, MVHR is increasingly specified as a compliant and high-performing ventilation strategy.
Is MVHR suitable for commercial buildings?
MVHR is used in a wide range of commercial applications including offices, schools, healthcare facilities, and mixed-use developments. Commercial projects typically require higher capacity units and more sophisticated controls integration.
Units with airflow rates up to 900 m³/h and compatibility with building management systems make MVHR a viable and energy-efficient ventilation strategy for many commercial building types.