Continuous extract fans (dMEV) in Greater London

A dMEV (decentralised mechanical extract ventilation) fan is a low-energy extract fan that runs continuously at a quiet trickle speed and boosts automatically when it senses humidity or a light switch. Because it never fully switches off, moisture is removed steadily instead of building up between showers.

If you are anywhere in Greater London, send the postcode and a few photos and we will tell you what we would recommend. Towns we cover include Archway, Sutton, Croydon, Brent and Islington.

dMEV fans in Greater London at a glance

Area: Greater London
Towns listed: 216, largest Brent
Postcode districts: SE7, CR0, CR9, BR2, BR4 and E10
Price region: London
Survey: Free survey (UK mainland)

What continuous extract fans (dMEV) involves

Landlords and housing associations often choose them because tenants cannot switch them off and forget them. Under Approved Document F, continuous mechanical extract systems need commissioning: the airflow on both trickle and boost is measured and recorded. We do that as part of the job, so you have a record for building control, a landlord file or a future buyer.

Commissioned and recorded

Trickle and boost rates measured and written on a commissioning sheet.

Bathroom and en-suite

Through-wall or ceiling fans with humidity-controlled boost.

Kitchen

Higher-rated continuous fans where a ducted hood is not practical.

Guide prices in Greater London

Continuous extract fans (dMEV) guide prices in Greater London
Work	Guide price
Continuous-running extract fan (dMEV) with humidity boost, flow tested (per fan)	£415–£725 inc VAT
Airflow testing and commissioning sheet for extract fans (up to 6 fans) (per home)	£175–£355 inc VAT

Guide prices using London rates. Prices include VAT at 20%. A guide price is not a quote: we confirm a fixed price in writing first.

Common reasons people call

An energy retrofit has made the house more airtight
Building control has asked for continuous extract
Occupants switch fans off because of noise

Rules in England

English building work follows Approved Document F (2021 edition) for ventilation rates, installation and commissioning. For homes, it sets minimum extract rates such as 15 litres a second for a bathroom and 30 or 60 for a kitchen, and expects mechanical systems to be airflow-tested.

How the job runs

Survey
Specify
Fit
Commission
Record

Towns we cover in Greater London

Questions about continuous extract fans (dMEV) in Greater London

Is the survey free in Greater London?

For new installations on the UK mainland, yes. The survey is free and the quote that follows is fixed and in writing. Servicing, testing and repair visits are charged, and we confirm the cost before booking.

What is the difference between dMEV and MEV?

dMEV uses one small fan in each wet room. MEV uses one central fan, usually in the loft, ducted to all the wet rooms. Both run continuously.

Do I still need trickle vents?

Yes. With continuous extract, Approved Document F still expects background ventilators in habitable rooms so replacement air can get in.

Which rules apply to ventilation in Greater London?

In England, ventilation in new and altered homes is covered by Approved Document F of the Building Regulations. Landlords also have duties under the Housing Health and Safety Rating System, and workplaces must be ventilated under the Workplace (Health, Safety and Welfare) Regulations 1992.

Which towns in Greater London do you cover?

All of Greater London, including Archway, Sutton, Croydon, Brent and Islington. If your town is not listed, send the postcode and we will confirm.