Continuous extract fans (dMEV) in Hertfordshire

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.

Every job in Hertfordshire gets a written quote before it starts and a commissioning record when it finishes. We cover Stevenage, St Albans, Welwyn Garden City, Cheshunt and Hatfield and the villages around them.

dMEV fans in Hertfordshire at a glance

Area: Hertfordshire
Towns listed: 32, largest Watford
Postcode districts: HA6, WD3, EN6, WD2, HP1 and HP4
Price region: East of England
Survey: Free survey (UK mainland)

How we do it

On trickle speed they are barely audible and use very little power; on boost they reach the higher continuous-extract rates in Approved Document F (in England, at least 13 litres a second for a kitchen, 8 for a utility room or bathroom and 6 for a WC). 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.

Kitchen

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

Whole-home dMEV upgrade

Every wet room converted at once, with trickle vents checked in the habitable rooms.

Commissioned and recorded

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

Guide prices in Hertfordshire

Continuous extract fans (dMEV) guide prices in Hertfordshire
Work	Guide price
Continuous-running extract fan (dMEV) with humidity boost, flow tested (per fan)	£360–£625 inc VAT
Airflow testing and commissioning sheet for extract fans (up to 6 fans) (per home)	£150–£310 inc VAT

East of England rates shown. Prices include VAT at 20%. The fixed price is confirmed in writing after we have seen the job.

When to get it looked at

Building control has asked for continuous extract
Occupants switch fans off because of noise
Mould keeps returning in a bathroom with a working fan

Rules in England

In England, ventilation is covered by Part F of the Building Regulations and its guidance, Approved Document F (2021 edition). It sets extract rates for kitchens, bathrooms and utilities and asks for mechanical ventilation to be commissioned and recorded.

How the job runs

Survey
Specify
Fit
Commission
Record

Towns we cover in Hertfordshire

Questions about continuous extract fans (dMEV) in Hertfordshire

Which rules apply to ventilation in Hertfordshire?

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.

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.

Can dMEV fans be fitted where a fan already exists?

Usually yes. Most fit the existing hole or duct, which keeps the cost and mess down.

Which towns in Hertfordshire do you cover?

All of Hertfordshire, including Stevenage, St Albans, Welwyn Garden City, Cheshunt and Hatfield. If your town is not listed, send the postcode and we will confirm.

Are prices different in Hertfordshire?

Our guide prices are adjusted by region. In Hertfordshire we use East of England rates, so continuous-running extract fan (dMEV) with humidity boost, flow tested is typically £360 to £625 inc VAT per fan.