Poor Air Extraction in Bathroom

Our extractor fan in the bathroom is really rubbish. We moved in almost two years ago and replaced the old loud fan with a new one as our electrician was already changing the lights in there anyway. However, I’m not sure it actually extracts too much air when the shower is on. Whenever we have even a short shower there is a lot of hot air trapped in the bathroom, and it stays for a long time, even with the door open. And when a longer shower is had (not looking at anyone in particular!) the room is full of steam.

Is there anything that we can do to improve the performance of the fan? Is it just that the duct out might not have been cleaned or something? Or do we need to put in a new fan that will actually get rid of the hot steam after a shower?

It’s been frustrating me for a while, but during the really cold spell it caused some drips into our bedroom roof where the steam had got into the loft space, condensed on the roof and run down to the bottom of the block foam insulation in the rafters and dripped at the end of the block onto the plasterboard below. I am also contacting a loft insulation people to see if we can sort the insulation out in there, but that won’t help the steam in the bathroom situation.

You can test easily whether the fan is extracting by taking a light plastic bag and placing it over the extract vent while the fan is running. If it is sucked onto the vent it is extracting (though not necessarily enough). If the bag is blown away from the vent the system is running the wrong way (!) and if it falls down there is negligible air movement.

What diameter is the vent and how long is the overrun when the light is switched off?

How airtight is the house? If you extract air, “new” air needs to be able to enter the house elsewhere.

Thank you Tim. The bag gets sucked in so it’s definitely working to some extent. Diameter of the Dan is just less than 10cm, and it leads to an airbrick in the wall. Having looked at it there’s definitely some dust and debris round the back for the fan but not loads.
Overrun is about 5 minutes I’d guess, but we leave the light on till the steam has dissipated to try and help. The house definitely isn’t airtight. It’s a 1930s house and we’ve added cavity wall insulation but thats about the extent of the Retrofit we’ve done.

The first thing to try is probably to remove the air brick and put a ventilation cowl over the end of the duct. An airbrick is not suitable for forced ventilation, although there are probably millions of such installations. While doing the job any debris in the duct can be removed.

Thinking about it, you have cavity walls, so unless the airbrick opening is lined some of your extracted air is being blown into the cavity , and due to the likely proximity of the fan to the roof some of that warm humid air is probably going straight into the roof :weary:

That feels unlikely that that is something I could do. But also feels like an awkward job that most tradespeople wouldn’t want to do on its own.
The cavity is filled, but based on the other issue I mentioned there is definitely some hot humid air escaping into the loft space and that could definitely be due to the fan

It is normal but very undesirable for humid air to get into the roof space from bathrooms. There is another thread active that is currently addressing the issue, although dodgy extract fan isn’t something being considered.

Cavity wall insulation added as a retrofit is never airtight nor a vapour barrier unless you have closed cell foam, which is a specialist product and very expensive. I would recommend it for most cavity walls if only it were affordable.

In general I find most extractor fans are rubbish… We are in a new build and still need to open the bathroom window for an hour or so after we have a shower.
Something like this that runs continiously (very low) might be worth a look: https://www.kair.co.uk/product/kair-smart-fan/

The specification and location of the fan are also important. In our ensuite we have ducting to an inline fan rated at 190m3/hour located directly over the shower cubicle. It’s set to run for 3 minutes after the showering has finished. It’s triggered by an infrared detector over the shower cubicle and seems to remove the worst of the humidity.

In our main bathroom, where the shower is only used by guests, the fan is only rated at 70m3/hour and I have it set to run for 8 minutes after showering. It’s not located over the shower cubicle and is definitely not as effective.

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My whole house MVHR is rated for maximum boost of 350m3/h. That is split over 4 extracts, let’s say 85m3/h each. None of the vents is directly over the shower/cooker and we never get enough steam to cause condensation. The ducts are 160mm diameter. There are 5-6 people generating water vapour.

I very rarely use the boost function, so clearly we don’t need as much as 350m3/h.

How long is “longer”? If you can’t put your foot down I suggest that you review the solutions discussed last year for limiting length of showers by cutting off the water automatically, or as I suggested, just cut off the hot water!

Edit: sorry, I just realised that was another forum but the idea still holds. Think timer and motorised water valve.

For showers and wet areas, I have experience of both single room heat exchange and standard extractors (100mm). Extractors must be appropriately sized for the room and preferably humidity controlled. There is a bit of learning involved with setting the humidity level, but they work well.

Feeling confused! Need to replace both kitchen and downstair shower room extractor fans in 1930s semi. Both 16 years old and not working well.
Downstairs shower room with sink and toilet, located in half of what was old kitchen before extension.
Extractor fan currently located above toilet slightly into window recess, furthest away from shower but this is a guest shower so rarely used. Ducting goes through internal wall into utility room and then turns 90 degree up into vent out into roof (single storey). Not sure if we should get an extractor fan like airflow 30 or look into heat recovery or what.
Large extension on side of house. Fan in wall above cooker about 140cm, Ducting straight outside through external wall. Also needs replacing. Lot of moisture from Utility area (same one as above) which is part of the kitchen in area that extends out the back and wraps along (what was) the outside back of old kitchen. Hope that makes sense. Thinking Fan Airflow 60 but should I think heat recovery.
Be very grateful for any throughts. Thanks

With the existing duct the downstairs shower room is not suitable for a freestanding heat recovery unit. If there is a bit of wall that goes straight to the outside then heat recovery is worth consideration.

The kitchen is more suitable for heat recovery although I don’t know of a 140mm unit. I suggest getting on some steps and measuring the exact size as 140mm is an unusual size.

On another thread several participants recommend a 150mm heat exchange system, by Kair

Thankyou I think I have misunderstood the use of heat recovery units. THanks for clarifying.
Mould and condensation are very bad in these areas so I think I need to get extractors in the meantime but if there is any recommendations on ones I should get that would be great
many so much

typo it is 150mm not 140mm. Thank you for noticing.

That’s good to see, then the 150mm Kair unit is more or less a straight swap.

? (Ducting goes through internal wall into utility room and then turns 90 degree up into vent out into roof)- Sounds like a source for condensation in pipe and around pipe. Is it insulated?

Good point and one I raised in another thread recently.

There should be absolutely no corrugated/concertina duct and the smooth duct needs angling to give free drainage. The section in the roof space also needs insulating to reduce condensation risk.