Everytime you take a shower, the walls and ceiling have lots of water on them. After the shower, some (not alot) of water will come dripping in from the extractor fan duct onto the floor.

  • Location UK
  • New build (built 2022). Very generally, it feels well built.
  • Bathroom size is ~4m * ~1.6m * ~2.1m. Considering the slanted ceiling and other bits, you can probably subtract about 20% of the volume of the room.
  • The extractor fan is mounted near the shower. I believe its this fan: https://www.airventventilation.co.uk/product/100mm-low-profile-axial-fan-with-timer-and-backdraught-shutter/
  • If I put a tissue to the extractor fan, it sucks the tissue up which I think tells me that there is nothing wrong with the fan, ducting or getting fresh air into the room.
  • The velux window in there has the trickle vent open and there is a small gap under the door for air replenishment.
  • I've tried increasing the underfloor heating temperature to 26*C (sensor is in the floor but the air temp will be lower) and that doesn't seem to have helped either.
  • Fan comes on when you turn the light on and stays on for 5mins after you turn the light off. By the time you turn off the shower, the walls/ceiling already have lots of water on.
  • Tried leaving the window open a little during the shower. With the air temperature outside that obviously drops the room temperature. Doesn't seem to help.

The paint is starting to crack/show signs of wear and we've only been in here a couple of months.

Surely there is something I can do here to prevent the condensation and damage from it?

  • 1
    How long is the fan working? Shower humid air will condense on any cooler surface. New build houses usually have some number of years warranty. Paint should not crack after a few months. Possible the fan is not big/powerful/not adjustedright enough and should be builders problem.
    – crip659
    Commented Jan 6, 2023 at 22:08
  • Fan comes on when you turn the light on and stays on for 5mins after you turn the light off. By the time you turn off the shower, the walls/ceiling already have lots of water on. I want to be informed about possible remediation steps for when I talk to the builder.
    – Cheetah
    Commented Jan 6, 2023 at 22:18
  • 2
    You have 15m3 bathroom size and a fan that does 90m3/h, so it will recycle the air in 90/15= 6 times in a hour. Way too slow to remove the condensation. Consider stronger fan that recycles the air like 20 or more times per hour.
    – Traveler
    Commented Jan 6, 2023 at 22:22
  • However all will depend on the exhaust duct length, the shorter the better.
    – Traveler
    Commented Jan 6, 2023 at 22:28
  • Longer running time might also do it, if that's easier... Condensation on walls happens when air is humid and walls are colder than air. Increasing the bathroom temperature should reduce that effect; increasing the fan will also help by reducing retained humidity.
    – keshlam
    Commented Jan 6, 2023 at 22:28

3 Answers 3


Condensation in bathrooms is always worse in the winter months for two main reasons: the air can't hold nearly as much moisture, and we like to take long hot showers when it's cold out.

The guidelines I'm seeing online (e.g., here, admittedly US-based results) specify a fan should exchange the air in the bathroom at least 8 times every hour:

A fan with the correct CFM should draw in enough air to refresh all the air in your bathroom at least eight times per hour.

Your fan is exchanging 6.5 times per hour (assuming the full volume of 13.4 m3, not taking into account your 20% reduction), which is a bit undersized according to that guideline. If you want the recommended 8 exchanges per hour, you're looking at a minimum of 108 m3/hr. If your bathroom is actually 20% less than the 13.4 m3 (4 x 1.6 x 2.1m), then your fan is exchanging more than 8 times per hour and is sized correctly.

Increasing the temperature set point of your in-floor heating won't help, since air is being pulled in from other rooms to replace the air exhausted by the fan. It will not heat up at all in 7 minutes. Increasing the temperature in the rest of your house may help, but I suspect it won't do much.

What you really need to do is run the fan for longer after you finish showering (I typically do 20 minutes, but some people on this site who live in colder climates will run the fan for an hour or two after showering in the winter), and shower with the bathroom door open. Having the door open will allow the humidity to not collect in the bathroom and instead disperse throughout the house. You may also consider taking (slightly) colder and/or shorter showers as well, as that will overall reduce the amount of humidity introduced into the bathroom.

  • Sorry - to be clear, I was stating what the overrun is set to. I normally leave the light on (and therefore the fan on) for much longer....but by this time the walls are already covered
    – Cheetah
    Commented Jan 7, 2023 at 10:31

You have 15m3 bathroom size and a fan that does 90m3/h, so it will recycle the air in 90/15= 6 times in a hour. Or only once in 10 minutes.

That might be good for toilet smells but too slow for condensation.

The problem is once the humidity has condensed on the walls, it will take very long time to remove it, till it has evaporated again.

I found one other model from same company (but it is your reparability to check if it fits).

This one is 10 times stronger than yours. 903m/hr

It will recycle the air once every minute, thus no condensation will happen.

Check the model and specifications in the link, I believe they made a error in the specs, so better verify


However this model looks more like to be correct specs.

I will give you air exchange very 3 minutes, which is more likely to stop the condensation.

But better check with building contractor if it will fit.

150 mm

  • Unfortunately it is a typo (3 in the wrong position)... its the same fan with a different grill. Upvoting cause its probably the issue here
    – Cheetah
    Commented Jan 6, 2023 at 23:13
  • @Cheetah I believe I pointed the manufacturer error
    – Traveler
    Commented Jan 6, 2023 at 23:16

It's a new build so I'm guessing this won't be an appealing answer. You don't say what sort of shower enclosure you have. I have a similar size bathroom to you, and no issues with condensation but we have an enclosed shower cubicle (apart from a 20cm or so gap between the frame and the ceiling). Perhaps you have an open shower without a door? I can see that would make the room steamy, perhaps you could replace or adapt the shower to have a door if it doesn't have one.

Where I've seen a similar situation to yours, bathroom paint helped quite a lot. It absorbs the moisture and releases it slowly over the day.

You can also get bathroom fans with humidistats that turn themselves on for as long as is required to get rid of the moisture.

Shorter showers would also help.

  • Its an open shower, not enclosed. The walls are already sodden by the time the shower is turned off, I'm not sure running the fan longer would help.
    – Cheetah
    Commented Jan 7, 2023 at 19:55
  • If you have painted walls, esp with bathroom paint, they will release the moisture over time. Running the extractor fan for longer will remove this moisture so that the walls are ready to receive the next load. Commented Jan 8, 2023 at 21:53
  • The other thing we do is to use a squeegee to remove the moisture from the shower enclosure. Only takes a few minutes, keeps the glass looking nice for longer, helps prevent mould and, because you're reducing the amount of work the extractor fan is having to do, will help dry the bathroom faster. A friend of mine uses a dehumidifier outside their bathroom. Commented Jan 8, 2023 at 21:59

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.