MVHR Ventilation Explained: What It Is, What It Costs and Whether You Need It

What Is MVHR?

Mechanical Ventilation with Heat Recovery (MVHR) is a whole-house ventilation system that simultaneously extracts stale air from wet rooms (bathrooms, kitchen, utility rooms) and supplies fresh filtered air to living spaces — while recovering up to 90% of the heat from the extracted air before it is expelled outside.

Without any ventilation, modern airtight homes accumulate moisture, CO2, and pollutants. Traditional "trickle ventilators" and window opening allow fresh air in but lose heat. MVHR solves both problems: it continuously renews indoor air while capturing most of the energy that would otherwise be lost.

How MVHR Systems Work

The system has two airflows running in opposite directions through a heat exchanger:

1. **Extract air:** Drawn from bathrooms, kitchen, and utility rooms — this air is typically warm and humid

2. **Supply air:** Fresh outside air drawn in and filtered before delivery to bedrooms and living areas

In the heat exchanger, the outgoing warm air transfers its heat to the incoming fresh air, without the two airstreams mixing. The result: fresh air delivered at close to room temperature even in cold weather, dramatically reducing ventilation heat loss.

Modern MVHR units achieve heat recovery efficiencies of 85–92%. The unit itself — typically installed in a loft, utility room, or cupboard — runs continuously at low speed, cycling up automatically when moisture sensors detect high humidity (during showering, cooking).

When MVHR Is Most Beneficial

MVHR delivers the greatest benefit in airtight buildings. The logic is straightforward: the more airtight the building fabric, the more ventilation depends on the mechanical system rather than adventitious gaps and cracks. In a well-built modern home (air permeability below 3 m³/m²/h at 50Pa pressure test), MVHR is often essential.

MVHR is standard specification in:

• Passivhaus-certified buildings
• New homes built to Part F of the Building Regulations (higher airtightness standards)
• Highly retrofitted properties with external wall insulation and triple glazing

For older draughty properties (Victorian terrace, pre-1990s semi-detached), the priority is typically fabric improvement first. Installing MVHR in a leaky building before improving airtightness is inefficient — the system cannot control airflow through adventitious gaps and its heat recovery function is undermined.

Costs: Installation and Running

**Installation cost (new build):** £3,000–£6,000 for a typical three-to-four bedroom home when installed during construction. Ducting is concealed within the building structure.

**Retrofit installation:** £5,000–£10,000+, as surface-mounted or boxed-in ductwork is required. Retrofit is most cost-effective in loft conversions, extensions, or whole-house refurbishments where ductwork can be integrated.

**Running cost:** Typically £50–£120 per year in electricity (the fan motors are low-wattage and run continuously at low speed).

**Filter replacement:** MVHR filters (G4/G4 or F7/G4 combination) should be replaced every 6–12 months. Filter costs are typically £30–£80 per set. The heat exchanger itself should be cleaned annually. Ongoing maintenance is often underestimated; budget £100–£200 per year for filter and maintenance costs.

MVHR vs MEV: Understanding the Alternatives

**MEV (Mechanical Extract Ventilation)** extracts stale air from wet rooms but does not supply air or recover heat. Supply air enters via trickle ventilators in windows. MEV costs significantly less (£1,000–£2,500 installed) but provides no heat recovery benefit.

**dMEV (Decentralised MEV)** uses individual fans in each wet room rather than central ductwork. Low cost, easy retrofit, no heat recovery.

The right system depends on the building's airtightness and energy efficiency ambitions. For a Passivhaus or near-Passivhaus standard home, MVHR is the correct choice. For a standard new-build or lightly retrofitted home, MEV or dMEV may be proportionate.

MVHR and EPC Ratings

MVHR systems can positively affect a property's EPC rating because the Standard Assessment Procedure (SAP) methodology accounts for reduced ventilation heat loss in airtight buildings with heat recovery. The benefit to the SAP score depends on the building's overall airtightness — in a truly airtight home, MVHR can contribute meaningfully to pushing an EPC from C to B or B to A.

If you are buying a new-build or recently renovated property and the specification mentions MVHR, you can check the current EPC rating through Property Passport UK to verify the assessed performance matches expectations.