Continuous extract fans (dMEV) in Northamptonshire

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.

Northamptonshire has every kind of building, from old terraces to new estates and business parks, and every job is designed around the building in front of us, not a standard kit.

dMEV fans in Northamptonshire at a glance

Area: Northamptonshire
Towns listed: 8, largest Northampton
Postcode districts: NN9, NN10, NN11, NN13, LE16 and NN16
Price region: East Midlands
Survey: Free survey (UK mainland)

What continuous extract fans (dMEV) involves

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.

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.

Whole-home dMEV upgrade

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

Guide prices in Northamptonshire

Continuous extract fans (dMEV) guide prices in Northamptonshire
Work	Guide price
Continuous-running extract fan (dMEV) with humidity boost, flow tested (per fan)	£340–£575 inc VAT
Airflow testing and commissioning sheet for extract fans (up to 6 fans) (per home)	£140–£290 inc VAT

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

When to get it looked at

Mould keeps returning in a bathroom with a working fan
You manage rental homes and want ventilation that cannot be switched off
You are refurbishing several wet rooms at once

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 Northamptonshire

Questions about continuous extract fans (dMEV) in Northamptonshire

Are prices different in Northamptonshire?

Our guide prices are adjusted by region. In Northamptonshire we use East Midlands rates, so continuous-running extract fan (dMEV) with humidity boost, flow tested is typically £340 to £575 inc VAT per fan.

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.

How much does a continuous extract fan cost?

A dMEV fan usually costs £345 to £595 including VAT per room, supplied, fitted and commissioned. Converting several rooms in one visit brings the cost per fan down.

Is the survey free in Northamptonshire?

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.

Which rules apply to ventilation in Northamptonshire?

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.