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What Is MVHR? — Mechanical Ventilation with Heat Recovery
A plain-English guide to MVHR systems: how they work, efficiency ratings, installation requirements, and Part F ventilation compliance in the UK.
Definition
MVHR (Mechanical Ventilation with Heat Recovery) is a whole-house ventilation system that provides continuous fresh air while recovering heat from the extracted stale air. The system uses a counter-flow or cross-flow heat exchanger to transfer heat from the outgoing exhaust air to the incoming supply air, typically recovering 85-95% of the heat energy. MVHR is the preferred ventilation strategy for highly insulated, airtight buildings and is increasingly common in new-build UK homes.
When Is It Used?
MVHR is used in new-build homes designed to high airtightness standards (typically below 3 m³/(h·m²) at 50 Pa), Passivhaus projects, and some retrofit projects. It is one of four ventilation strategies recognised by Part F of the Building Regulations (System 4). MVHR is particularly beneficial where trickle vents and extract fans alone cannot provide adequate ventilation without excessive heat loss, and in urban environments where opening windows is undesirable due to noise or air quality.
Key Facts
- Heat recovery efficiency: typically 85-95% (SAP Appendix Q listed units)
- Specific Fan Power (SFP) should be below 0.7 W/(l/s) for Part L compliance
- Ductwork should be rigid metal (galvanised steel or aluminium) for best performance
- Supply air to bedrooms and living rooms; extract from kitchen, bathroom, utility, and WC
- Part F minimum whole-dwelling ventilation rate: typically 13-29 l/s depending on number of bedrooms
- Summer bypass mode allows cool night air to enter without passing through the heat exchanger
- Filters must be cleaned or replaced every 3-6 months
- Typical electricity consumption: 30-60 kWh per year (less than a fridge)
Related Calculators
Use the Ventilation Rate Calculator for Part F airflow requirements, or the Heat Loss Calculator to see the impact of heat recovery on heating demand. You can also use the SFP Calculator to check specific fan power against the Part L limits. See also the Airtightness glossary entry.
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Frequently Asked Questions
An MVHR system continuously extracts stale air from wet rooms (kitchen, bathroom, utility) and supplies fresh filtered air to habitable rooms (bedrooms, living room). The extract and supply air streams pass through a heat exchanger where heat from the outgoing air is transferred to the incoming air without the two streams mixing. This recovers typically 85-95% of the heat that would otherwise be lost through ventilation.
MVHR is most cost-effective in well-insulated, airtight buildings where ventilation heat loss represents a significant proportion of total heat loss. It is generally considered worthwhile when air permeability is below 3 m³/(h·m²) at 50 Pa. In leaky older buildings, the heat recovery benefit is undermined by uncontrolled air leakage, making simpler ventilation strategies (MEV or dMEV) more appropriate and cost-effective.
A typical domestic MVHR installation costs £4,000-£8,000 including the unit, ductwork, valves, and commissioning. The MVHR unit itself costs £1,000-£3,000 depending on capacity and brand (Vent-Axia, Nuaire, Zehnder, Brink are common UK brands). Rigid metal ducting is preferred over flexible plastic for better airflow and lower noise, but costs more. Running costs are typically £30-£60 per year for electricity.
Yes, regular maintenance is essential for MVHR to work effectively. Filters should be cleaned or replaced every 3-6 months (more frequently in urban or high-pollution areas). The heat exchanger should be cleaned annually. The unit should be professionally serviced every 2-3 years, including checking fan speeds, duct connections, and commissioning airflow rates. Many units have filter indicator lights to remind you.
It is possible but challenging and expensive. The main difficulties are routing ductwork through the existing structure (typically requiring void above ceilings or boxing in), achieving adequate airtightness (the building envelope must be improved first), and finding space for the MVHR unit (typically a utility room, airing cupboard, or loft). Single-room heat recovery units (dMVHR) are an alternative for retrofit situations.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.