What MVHR does and when it makes sense
MVHR continuously extracts air from kitchens and bathrooms while supplying fresh filtered air to bedrooms and living rooms — recovering 80–90% of the heat from the outgoing air via a counterflow plate heat exchanger. Makes sense in: airtight modern extensions and renovations where natural ventilation is insufficient; properties with damp, condensation or air quality issues; whole-house renovations achieving EnerPHit or Passivhaus targets; flats where window opening for ventilation is impractical. Less suitable for: very leaky Victorian properties without air sealing (the heat recovery efficiency drops below useful levels); single-room retrofits.
Cost breakdown
Equipment: MVHR unit (Vent-Axia, Brink, Zehnder, Vaillant) £900–£3,500 depending on flow rate and efficiency. Ducting: rigid 125mm or semi-rigid 75mm radial ducting £800–£2,500 depending on house size and routing complexity. Diffusers and grilles £200–£500. Installation labour £1,200–£3,500. Commissioning to test air flow rates and balance the system £400–£800. Total retrofit on a 3-bed terrace £4,000–£8,000; on whole-house renovation with full ducting hidden in joists and ceiling voids £8,000–£18,000. Best installed during structural renovation when floors are up and ceilings are being relined — retrofit on a finished house is 30–50% more expensive due to access.
MVHR design rules for London properties
Airtightness target: aim for 3 m³/h/m² @ 50Pa or better — Victorian terraces typically need draughtproofing, sealing of services penetrations and continuous vapour control layer to achieve this. Boost flow rates: kitchen 60 l/s, bathroom 15 l/s, en suite 8 l/s — sized by floor area and occupancy. Heat recovery efficiency: target 85%+ certified by Passivhaus Institute or BSRIA. Filter spec: F7 supply side as standard, can upgrade to F9 in London air quality zones. Acoustic separation: cross-talk attenuators on all bedrooms, 25mm acoustic foam on supply ducting near bedrooms. Maintenance: filter change every 6 months £60–£120; full service every 3 years £180–£400.
