Almost every mouldy bathroom we are called to look at has the same root cause, and it is not cheap tiles or bad silicone. It is a fan that never moved enough air. Ventilation is cheap at build stage and expensive to retrofit, so it is worth understanding before your fit starts.
How much air actually needs to move
A hot shower puts a remarkable amount of water into the air, easily half a litre in ten minutes. That moisture has to leave the room within a reasonable time or it condenses on the coldest surface available, typically the window reveal, the ceiling above the shower, or the outside corner behind the door. The regulatory minimum for a bathroom is 15 litres per second. That is the floor, not the target.
The important catch is that manufacturers quote free air performance, measured with nothing attached. Add three metres of ducting and two bends and a fan rated at 21 litres per second may deliver barely 12. We size for the installed condition, not the box.
Fan types
- Axial. The standard wall or ceiling fan. Fine for short duct runs up to about 1.5 metres straight out through a wall.
- Centrifugal. Higher pressure, holds performance over longer duct runs and vertical rises. The right choice for a ceiling fan ducting out through a soffit or roof tile.
- Inline. Motor sits in the loft with a discreet ceiling grille in the room. Quietest option in the bathroom itself, ideal above a shower.
- dMEV continuous. Runs constantly at a trickle and boosts when humidity rises. Excellent in airtight modern homes and very quiet.
Controls that make the difference
A humidity sensor is the single best upgrade. It runs the fan when the air actually needs clearing rather than when someone happens to switch a light on. Pair it with a 15 to 20 minute overrun so the room is cleared after you have left, and a manual boost so it can be triggered without the light. Avoid a pull cord fan with no timer, because it will be switched off before it has done anything useful.
Ducting, where most installs fail
- Use rigid duct wherever possible. Flexible duct has ribbed internal walls that create resistance, and it sags into low spots that collect condensate.
- Keep the run as short and straight as you can, and use swept bends rather than sharp elbows.
- Insulate any duct running through a cold loft, otherwise moist air condenses inside the pipe and drips back into the fan.
- Give the duct a slight fall towards the outside so any condensate drains away from the house.
- Fit an external grille with a decent free area. A fine mesh anti insect grille can halve the flow, and they clog with dust.
Fan position
Air should travel across the room to the fan, so put the extract as far as practical from the door and as close as sensible to the shower. Fitting the fan next to the door means fresh air is pulled in and straight back out without ever passing over the wet zone. Leave a 10mm gap under the bathroom door so replacement air can get in, otherwise even a strong fan is trying to pull against a sealed room.
Noise
Fan noise is measured in decibels at three metres. Under 30dB is genuinely quiet, 35dB and up becomes intrusive and people stop using the boost. An inline fan in the loft is the most effective way to get high extraction with low in room noise, which is why we recommend it in en suites next to bedrooms.
Retrofitting into an older Stoke house
Solid brick terraces and 1930s semis often have no existing fan at all, just a window. Where an external wall is available a core drilled through wall fan is straightforward. Where the bathroom is internal we usually run an inline fan through the loft to a roof tile vent. Both are far cheaper done during a refit while ceilings and walls are already open.
Have it done properly
Every bathroom we fit includes correctly sized extraction, rigid ducting, a humidity sensor and full electrical certification as standard. Free survey and a fixed written price within 24 hours anywhere across Stoke-on-Trent and North Staffordshire.
Common questions
What extraction rate does a bathroom need?
Building regulations set 15 litres per second as the minimum intermittent rate for a bathroom, and 6 litres per second for a utility. In practice we specify above the minimum, because rated performance is measured without any ducting attached.
Is an opening window enough?
Not on its own for new work. Regulations require mechanical extraction in a bathroom whether or not there is a window, and in a Stoke winter nobody leaves a window open long enough to clear the moisture anyway.
Should the fan run with the light?
A humidity sensing fan with an overrun timer is better. Light linked fans stop the moment you leave, which is exactly when the room is at its wettest.
Why does my fan not seem to pull anything?
Usually long runs of flexible ducting, sharp bends, a blocked external grille, or a fan sized for a cloakroom fitted in a family bathroom. Rigid duct and a short straight run fix most cases.
Can the fan duct into the loft?
No. It must terminate outside through a wall, soffit or roof tile vent. Venting into a loft dumps litres of moisture into your roof structure every week.
Do you certify the electrical work?
Yes. Bathroom fan wiring is notifiable, and our own electricians test and certify it as part of the fit.