Can You Install Multiple Extractor Fans In Your Bathroom?
A second fan can clear stubborn condensation in a big or windowless bathroom as long as the ducting is planned properly.
Written by Richard Morgan
Updated
The short answer
Yes, you can install two extractor fans in one bathroom, and it's a sensible fix for a large or windowless room where a single fan can't clear the condensation. Give each fan its own duct to the outside rather than joining them into one shared run, choose two fans of equal power that run at the same time, and position both within the bathroom zone rules.
A bathroom that drips with condensation after every shower ends up with black mould on the ceiling, peeling paint and a damp, musty smell that never quite goes. When the fan that's already there can't keep up, adding a second one is a fix worth considering, although it isn't the right answer in every room.
The photo under the title comes from one of our own rental properties, where we fitted two fans high up at either end of the same bathroom wall. The tenant had been having to clean mould off the walls and ceiling again and again because the steam wasn't being cleared. With no window and enough floor space to justify a second fan, that bathroom was a good candidate.
Plenty of bathrooms aren't, either because there's no sensible route for a second duct or because the real problem lies with the fan that's already fitted. The sections below cover what to think about before you commit.
Wiring And Positioning A Second Extractor Fan
Where a fan is already in place, the power supply is there too, so a second fan is a fairly simple addition. The wiring is extended from the existing fan to the new one, and the new fan gets its own run of ducting to the outside. Bathroom electrics come under Building Regulations, so if you're not qualified, have an electrician wire the new fan in and sign the work off.
Position matters as much as the wiring. There are strict rules on where an extractor fan can go in relation to the bath and shower, based on the bathroom zones, and the rating of the fan you can fit depends on which zone it sits in. Placing each fan near the source of the steam and away from the door, so air is drawn right across the room, gets the most out of both.
Why Two Fans Shouldn't Share One Duct
Joining two extractor fans into a single duct looks like a shortcut, and it saves cutting a second hole through the wall. We wouldn't do it. Two fans pushing into the same pipe create uneven pressure, so one ends up fighting the other. Air can be forced back through the weaker fan, and both motors work harder than they should until one of them fails.
A shared duct also traps more moist air, which condenses inside the pipe and can run back towards the fans. On top of that, fitting a fan in a way the maker doesn't allow for can void the warranty.
Give each fan its own duct to the outside instead. That way both work as they were designed to, and the ducting stays drier. We'd also fit two fans of the same power and wire them to run together, so neither one is left doing all the work.
Upgrading Your Existing Bathroom Fan Instead
A second fan isn't always needed. Swapping a tired or underpowered fan for a stronger, better designed model can clear the steam on its own, without another hole in the wall or extra wiring. Our roundup of the best bathroom extractor fans covers the units we've fitted and tested, including quieter models with humidity sensors that switch themselves on.
Check The Fan You Already Have
Before buying a new fan or a second one, take a proper look at the fan that's there now. Dust and fluff build up on the grille and blades over time and choke the airflow, and a good clean can bring a sluggish fan back to life. Check the outside vent as well, because a blocked or stuck shutter stops the air getting out.
Motors wear out too, and some fans are faulty from the day they're fitted without anyone noticing. Hold a sheet of toilet paper up to the grille with the fan running, and if it barely moves, the fan isn't pulling enough air. A crushed or very long run of flexible ducting has the same effect, so follow the duct where you can reach it.
Dealing With The Damage Condensation Leaves Behind
Better ventilation stops the problem getting worse, but it won't clear mould that's already there. Treat existing patches with a mould remover for walls and ceilings, then repaint with an anti-mould paint made for damp rooms once the surface is dry. If the ceiling paint has started to flake, our guide on why bathroom ceiling paint peels explains how to put it right.
Is A Second Extractor Fan Worth Fitting
Two fans make sense in a large bathroom with no window, where one fan can't move enough air however good it is. In a smaller room, cleaning or upgrading the existing fan is the cheaper and simpler fix. Either way, give each fan its own duct to the outside and keep the airflow clear, and the condensation has somewhere to go.
Watch Us Do It
TESTING Bathroom Extractor Fans - Can They Really Be SILENT yet POWERFUL? #shorts #extractorfans
Other Questions We Get Asked
Can two bathroom extractor fans share the same ducting?
Two bathroom extractor fans shouldn't share the same ducting. The fans create uneven pressure in the shared pipe, so one works against the other, air can be pushed back through the weaker fan and the motors strain until one fails. A shared duct also traps more moisture, and the setup can void the fan warranty, so give each fan its own route outside.
Do you need a window in a bathroom with an extractor fan?
A bathroom doesn't need a window as long as it has mechanical extraction that can clear the steam. Windowless bathrooms rely entirely on the fan, which is why they're the ones most likely to need a stronger unit or a second fan. Leaving the fan to run on after a shower helps clear the last of the moisture once the room is empty.
Why is my bathroom extractor fan not clearing the steam?
A bathroom extractor fan that isn't clearing steam is clogged, worn out, too weak for the room or connected to poor ducting. Clean the grille and blades, check the outside vent isn't blocked and look for crushed or overly long flexible duct. If the fan still struggles, replace it with a more powerful model or add a second fan with its own duct.
Can I fit a second extractor fan myself?
You can do the physical work of fitting a second extractor fan yourself, including cutting the hole and running the ducting. The electrical connection is a different matter, as bathroom wiring comes under Building Regulations and the fan has to suit the zone it's in. Unless you're qualified, have an electrician connect the fan and sign off the work.
Where did you fit the two fans in your own bathroom?
High up at either end of the same wall, in a windowless bathroom in one of our rental properties that was large enough to justify a second fan. In your own room, get each fan close to where the steam comes from and away from the door, so the air is pulled right across the room.
Should the two fans be the same power?
Yes. Matched fans wired to run together share the load, where a mismatched pair leaves one doing most of the work. Give each its own duct outside too, because a shared duct is where the pressure problems start.
How can I tell if my existing bathroom fan is too weak?
The toilet paper test is the quickest check. With the fan running, hold a sheet up to the grille, and if it hardly moves, not enough air is being pulled through. Before you blame the fan itself, clean the grille and blades, free up the outside vent shutter and look along the duct for crushes or an overlong run.
Will a second fan get rid of the mould that's already on my ceiling?
No. A second fan stops the mould getting worse, but the patches already there need killing with a mould remover made for walls and ceilings. Once the surface is dry, repaint with an anti-mould paint, and treat any flaking ceiling paint as a separate job.
Richard has spent years renovating properties and turning them into rentals and Airbnbs. Like a lot of people he started out as a beginner, and these days there isn't much DIY he won't take on.