What is MVHR, and how does it actually work?
Mechanical Ventilation with Heat Recovery (MVHR) gives your home a constant supply of fresh, filtered air while holding on to the heat you have already paid for. Here is how it works, what it costs to run, and when it is the right choice for a UK home.
How an MVHR system works
An MVHR system is a single ventilation unit connected to two sets of ducts. One set extracts humid, stale air from wet rooms — kitchen, bathrooms, utility and en-suites. The other set supplies fresh, filtered air to living rooms and bedrooms.
Inside the unit, those two airstreams pass through a heat exchanger. They never mix: the plates of the exchanger simply let warmth pass from the outgoing air into the incoming air. In winter, air drawn in at 5°C can arrive in your bedroom at around 18°C without the heating doing the work. In summer, a summer bypass lets cooler night air through untreated.
- 1. Extract. Moist, stale air is pulled from wet rooms.
- 2. Recover. The heat exchanger captures the warmth from that air.
- 3. Filter. Fresh outdoor air is drawn in and filtered.
- 4. Supply. Pre-warmed, clean air is delivered to bedrooms and living spaces.
The benefits, in practice
Keeps the heat you paid for
The heat exchanger transfers warmth from outgoing stale air into the incoming fresh air, typically recovering 85–93% of it. You ventilate without throwing your heating out of a window.
Filtered, cleaner air
Incoming air passes through filters that catch pollen, dust and much of the fine particulate from traffic — useful for hay fever and asthma sufferers, and for homes near busy roads.
No more condensation and mould
Moisture from showers, cooking and drying laundry is removed continuously, so humidity stays in a healthy range and mould loses the damp it needs to grow.
Quiet, constant, automatic
A well-designed and commissioned system runs quietly in the background at low speed, boosting when needed. No open windows, no noise, no draughts.
Energy use and running costs
MVHR runs continuously, but at very low power. A typical domestic unit draws a few watts per litre per second of airflow, which for most homes works out at roughly £30–£70 a year in electricity — comparable to leaving a couple of low-energy bulbs on. Against that, the heat recovered from extracted air reduces the load on your heating through the whole heating season.
Two things decide whether you see those savings: how airtight the property is, and how well the system is commissioned. An MVHR system in a leaky house loses the recovered heat through the fabric, and an uncommissioned system can run fans harder than needed, using more electricity while under-ventilating some rooms. Commissioning is not paperwork — it is where the efficiency comes from.
Is MVHR right for your home?
MVHR suits airtight properties: new builds, deep retrofits, extensions with high insulation levels, and flats with persistent condensation. If your home is draughty and uninsulated, improving airtightness first will make the system far more effective — or a simpler extract system (MEV) may be a better fit.
Ductwork routes matter too. Rigid or semi-rigid ducts with gentle bends, planned early, give quiet and efficient performance. Retrofitting into finished ceilings is possible, but the design work needs doing before anyone lifts a floorboard.
Common questions
- How much heat does MVHR recover?
- Modern units recover 85–93% of the heat in extracted air.
- Will it stop condensation and mould?
- Yes — by removing moist air continuously it keeps humidity in a healthy range, which is exactly what mould needs to be denied.
- Is it noisy?
- A correctly sized, well-ducted and balanced system is barely audible. Noise almost always points to undersized ducts, sharp bends or a system running too hard because it was never commissioned.
- How often does it need servicing?
- Filters every 6–12 months, with an annual service and airflow re-check.
Thinking about MVHR for your home?
We install, commission and service MVHR across Stevenage, Hertfordshire and London — and we are happy to tell you when it is not the right answer.