dMEV Continuous Extractor Fans

Frequently asked questions

What is a dMEV fan?

dMEV stands for decentralised mechanical extract ventilation. It is a single room extractor fan that runs continuously at a low trickle rate to keep moisture levels down, then boosts to a higher rate when the room is in use, when humidity rises or when someone walks in. "Decentralised" means each wet room has its own fan, rather than one central unit serving the whole property.

What is a trickle fan?

"Trickle fan" is the everyday name for a dMEV or continuous running fan. The trickle speed is the low background rate it runs at all day, and the boost speed is the higher rate it switches to when the room is being used. Most dMEV fans let the installer set both speeds on site to suit the room.

dMEV or intermittent extractor fan?

An intermittent fan only runs when it is switched on, usually with the light, so moisture left after a shower sits in the room once it stops. A dMEV fan never stops, so the room is always being ventilated at a low level. Approved Document F allows either, and sets minimum continuous high rates for dMEV of 8 l/s for a bathroom, 13 l/s for a kitchen, 8 l/s for a utility room and 6 l/s for a toilet. Where condensation and mould are already a problem, or occupants tend to switch fans off, dMEV is the better choice.

Why are dMEV fans used in social housing?

Because they keep working without anyone having to use them. Intermittent fans are often switched off, isolated or left broken, which is one of the most common causes of damp and mould complaints. A continuous fan running at a low, quiet trickle keeps humidity down all the time. With Awaab's Law now requiring social landlords in England to investigate and fix damp and mould hazards within set timescales, dMEV fans are a common part of the fix in bathrooms and kitchens.

How much does a dMEV fan cost to run?

Very little. dMEV fans use EC motors, and at trickle speed most draw only a few watts, similar to a phone charger left plugged in. The exact power draw at trickle and boost is listed on each product page. Running continuously at low speed is also why they are quiet enough that most people stop noticing them.

Can a dMEV fan replace my existing extractor fan?

Usually, yes. Most dMEV fans here are 100mm and fit the same wall or ceiling hole as a standard 100mm bathroom fan. The wiring is the thing to check: a dMEV fan needs a permanent live supply so it can run all the time, plus a switched live from the light switch if you want it to boost when the light is on. Humidistat and PIR models can boost on their own without a switched live.

Which dMEV fan should I choose?

The Greenwood Unity CV2GIP and CV3 are "any room" fans set up for a bathroom, kitchen, utility or toilet at installation, and the CV2SVGIP is the 24V SELV version for fitting close to a bath or shower. The Elta FLUX 100 is a compact 100mm trickle and boost fan and the Elta DEXA 150 is a 150mm fan with humidity control for larger rooms. The S&P ECOAIR range is centrifugal, so it holds its airflow better on longer ducted runs, and comes with humidistat, PIR, timer and pull cord options.

Are dMEV fans noisy?

At trickle speed they are designed to be close to silent, because they run all day in occupied rooms. They are louder on boost, as any fan is, but only while the room is in use. For the quietest result, set the trickle speed no higher than the room needs and keep the duct run short and straight.

Do you supply dMEV fans for housing and refurbishment programmes?

Yes. We supply housing providers, M&E contractors, electricians and facilities teams, and hold stock across the main dMEV ranges for next working day delivery. Send us a property list or a schedule and we will price the lot, including ducting, wall kits and grilles. Call 0161 399 3825 or email hello@efans.co.uk.