The gold standard for new builds; and the deep-retrofit upgrade that lasts a generation.

MVHR is two ducted systems running through one unit. Stale, humid air is extracted from kitchens, bathrooms and utility rooms. Fresh, filtered air is supplied to bedrooms and living areas. As the two air streams pass each other in the heat-exchanger core, up to 90% of the heat in the outgoing air is transferred to the incoming air. You get fresh air without the heating bill of opening every window.

What it doesn't do: heat your home, cool your home, dehumidify your home in any meaningful way, or fix a damp problem caused by leaky walls. It is a ventilation system. The heat-recovery bit is a bonus that pays for the fan running costs, not a heating strategy.

MVHR only works if the house is airtight enough that the system controls the air movement, not the wind. The accepted UK threshold is around 3 air changes per hour at 50 Pa pressure (3 ACH @ 50Pa); anything leakier and uncontrolled draughts overwhelm the system, killing both the heat recovery and the filtration benefit.

Typical UK existing housing tests at 8–15 ACH. Modern building regs require new builds at 8 ACH. Passivhaus is 0.6. The gap between 'normal British house' and 'MVHR-ready' is real, and closing it (taped membranes, sealed service penetrations, airtight skirting) is the actual cost driver of an MVHR retrofit.

If you're not closing that gap as part of the project, fit PIV or extract fans instead. They're designed for leaky houses; MVHR isn't.

The unit itself is a £1,500–£3,500 box. The ducting that connects it to every room is where 60% of the install cost sits, and where 90% of bad MVHR installs go wrong. Long duct runs, sharp bends, undersized pipework and acoustic crosstalk between rooms all silently sabotage the system's performance.

A good designer will specify: rigid (not flexible) primary ducts, semi-rigid radial ducting to each room, dedicated supply and extract runs to every space (no daisy-chaining), attenuators between the unit and the manifolds, and isolators between rooms to stop bedroom-to-bedroom sound transmission.

If the quote says 'flexible ducting throughout' or doesn't include attenuators, you're being sold a budget install that will be loud and inefficient. Walk away.

An MVHR system has to be commissioned: each room's supply and extract valves are adjusted with an anemometer until the actual flow matches the design intent within ±10%. This typically takes a competent commissioning engineer 3–5 hours and costs £400–£800.

Half of UK MVHR installs are never commissioned. The unit is switched on, the valves are left at factory default, and the system runs forever at the wrong flow rates; too much air in one bedroom, not enough in the kitchen, condensation in the wrong places. Insist on a commissioning certificate before final payment.

MVHR units use two filter classes: G4 (pollen and dust) and F7 (fine particulates, including PM2.5). Change them every 6–12 months; they cost £25–£60 a set. Skip changes for two years and the fans work harder, electricity use doubles, and the heat-recovery efficiency drops noticeably.

The unit itself should last 15–25 years. The heat-exchanger core needs an annual vacuum/wash. The condensate drain needs to stay clear. None of this is hard, but it's not zero-touch; budget £80–£150 a year for filters and a half-day of your time for the annual service.