MVHR — what it is and when it's the right answer
Mechanical Ventilation with Heat Recovery is a whole-house ducted system that extracts stale air from wet rooms (kitchens, bathrooms, utility) and supplies tempered fresh air to dry rooms (bedrooms, living areas). The two airflows pass through a heat exchanger inside the MVHR unit — usually mounted in a loft or service cupboard — where 85–92% of the heat from outgoing air is recovered to warm incoming air. It's the right answer for well-insulated new-builds, major refurbishments, Passive House projects and any home where condensation, stuffy air or hay fever is a real problem. It's a significant install — usually fitted during a build — but transforms how a building feels to live in.
Commercial extract — kitchens, salons, treatment rooms
Commercial kitchen extract is specified to capture and remove heat, steam and grease vapour from cooking — usually via a stainless steel canopy with grease filters above the cooking line, ducted to a high-capacity extract fan venting above roof level. Sizing is calculated against cooking line length and equipment type (gas vs electric, char-grill vs induction, etc.). Salons and beauty treatment rooms have lower-volume but more sensitive extract requirements — removing chemical fumes from colour treatments, nail products and waxing, often with activated carbon filtration. Both must be balanced with matched make-up air supply, or the extract physically can't pull.
MEV (Mechanical Extract Ventilation) and dMEV — the simpler retrofit options
MEV is a single central fan with ductwork to extract grilles in each wet room — quieter than individual bathroom fans, more reliable and easier to maintain. dMEV is decentralised — individual continuous-running fans in each wet room. Both are simpler retrofits than MVHR for existing houses where running supply ductwork to every dry room isn't practical. They don't recover heat (so you do lose warm air to atmosphere) but they're significantly cheaper to install and dramatically better than the alternative of bathroom fans you turn on and forget about.
Filtration classes — what F7, G4 and HEPA actually mean
Ventilation system filters are graded to EN 779 / ISO 16890. G4 is a coarse pre-filter (captures lint, hair, large dust). F7 is a fine filter (captures most pollen and PM10 particulates) — the standard recommendation for MVHR fresh-air intake in pollen-sensitive households. F9 captures finer PM2.5 particulates. HEPA filters (H13/H14) are used in clinical environments — they capture 99.95%+ of all particles down to 0.3 microns, including bacterial and viral aerosols. We specify filter classes against the local environment (coastal salt, agricultural pollen, urban PM2.5) and the building use.
How ventilation works alongside air conditioning
Air conditioning and ventilation do different jobs and shouldn't be confused. Air conditioning controls room temperature by recirculating and tempering the air already in the room. Ventilation brings fresh air in from outside and removes stale air to outside. A building with great air conditioning and no ventilation feels cool but stuffy; a building with great ventilation and no air conditioning feels fresh but hot. We design both together — the air conditioning handles temperature, the ventilation handles air quality, and the two systems are sized and zoned to complement each other.
Part F, Part L and Building Regulations compliance
Building Regulations Part F (ventilation) and Part L (conservation of fuel and power) together require mechanical ventilation on most new-build dwellings, major refurbishments and most commercial fit-outs. The system must be designed to a specified air-change rate per building type, commissioned with measured airflows at every grille, and signed off by an appropriately qualified person. We design, install and provide commissioning paperwork that meets both — meaning your building control sign-off doesn't stall on the ventilation package.
