Bathroom Extractor Fans

Frequently asked questions

What size bathroom extractor fan do I need?

The size is the diameter of the spigot or duct the fan connects to. 100mm (4 inch) is the standard for bathrooms, en suites and toilets and fits most existing wall and ceiling holes. 125mm and 150mm fans move more air and suit larger bathrooms, wet rooms and longer duct runs. Match the fan to the duct that is already there where you can, and never reduce a 125mm or 150mm fan down to 100mm ducting, because it throttles the airflow and adds noise.

How powerful does a bathroom extractor fan need to be?

Approved Document F (Building Regulations Part F) sets a minimum intermittent extract rate of 15 l/s, which is 54 m³/h, for a bathroom or shower room, and 6 l/s for a toilet. That is the rate the fan must deliver once it is installed, not the free-air figure on the box, so allow for the duct: a basic axial fan on a long run with bends can drop well below it. For ducted ceiling installs or runs longer than a couple of metres, a centrifugal fan such as the S&P ECOAIR or Vent-Axia Quadra holds its airflow far better than an axial fan.

Timer, humidistat or PIR: which control do I need?

A timer fan runs for a set period after the light goes off, which clears the steam a shower leaves behind. A humidistat fan switches on when humidity rises and runs until it falls, so it works even when nobody touches the switch, and it is the better choice for a bathroom prone to condensation. A PIR fan starts when someone walks in. A basic fan with none of these runs only while it is switched on. Many fans combine two, for example humidistat with timer overrun.

What is a continuous running (dMEV) extractor fan?

A dMEV (decentralised mechanical extract ventilation) fan runs all the time at a low trickle speed and boosts to a higher speed when the room is in use or humidity rises. Part F sets a minimum continuous high rate of 8 l/s for a bathroom. dMEV fans use EC motors, draw very little power, and are the usual specification in new build, refurbishment and social housing, where intermittent fans often get switched off or left unused. The Greenwood Unity, Elta FLUX and DEXA, and S&P ECOAIR ranges all work this way.

Which extractor fan can go over a shower or in a wet room?

It depends on the bathroom zone. Zone 1, directly above the bath or shower tray up to 2.25m, needs a fan rated at least IPX4, and many manufacturers require a SELV (12V) model with its transformer outside the zones. Zone 2 also needs IPX4. In a wet room the whole floor can be a wet area, so an inline fan in the ceiling void, with only a grille in the room, is often the neater answer. Each product page lists the IP rating.

What is the quietest bathroom extractor fan?

Noise is measured in dB(A). Below about 30 dB(A) a fan is barely audible over normal bathroom noise, 30 to 35 dB(A) is a low background hum, and above 40 dB(A) most people notice it. The S&P SILENT range and the Systemair BF Silent are built for low noise. For the quietest result, a larger fan running slowly beats a small fan running flat out, and an inline fan in the loft keeps the motor out of the room altogether.

Wall, ceiling or window mounted?

Most fans here fit either a wall or a ceiling. A wall fan on an outside wall is the simplest install: a short sleeve straight through to a grille outside. A ceiling fan needs ducting across the loft or void to an outside wall or roof terminal, so choose a centrifugal model if the run is long, and insulate the duct through a cold loft so condensation does not run back into the fan. Window fans fit through a hole cut in a single pane of glass.

Why does a bathroom fan need a backdraft shutter?

A backdraft shutter closes when the fan stops, which keeps cold air, draughts and insects from blowing back into the room through the duct. It matters most on exposed or windy elevations and on fans that run only intermittently. Many S&P fans in this range have one built in. Continuous running dMEV fans usually rely on their own internal backdraft damper.

Can I use a bathroom extractor fan in an en suite or toilet?

Yes. An en suite or shower room needs the same 15 l/s intermittent extract as a bathroom, and a toilet needs 6 l/s, so a standard 100mm bathroom fan covers both comfortably. For a windowless toilet or en suite, a fan with a timer or PIR makes sure it runs long enough after each use.

Do you supply bathroom extractor fans for trade and housing projects?

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