tl;dr Why am I prohibited from using electric fan in natural / gravitational ventilation system, if there is an additional 2,5 meter long horizontal pipe between ventilated bathroom and the wall?

Two years ago I have purchased a flat and ordered team to perform general renovation works that included setting up inner walls and building additional electric, water, ventilation etc. installation (initially flat had only external walls and very basic installation and was not ready to move in).

As a part of these works, an additional, inner bathroom (no windows) was added. It was equipped with nearly 2,5 meter long horizontal pipe that goes through pantry room and connects that bathroom with vertical ventilation pipe in wall.

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Ventilation system's exit was equipped with electric fan on bathroom side (here fan is removed):

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Few days ago, I have received a written request to remove electric fan with the explanation that:

(all cites are my translations from foreign language; please forgive me for any mistakes in wording)

Natural ventilation system is all that is needed for ventilation like that. Flats in houses having natural / gravitational ventilation system are not allowed to have electric fans anywhere within ventilation system.

I have contacted person responsible two years ago for renovation works and the designer of above pictured horizontal pipe and I have got following explanation:

Natural ventilation system works by itself (and shouldn't be supported by electric fans) only if vertical ventilation pipe is placed in any wall that is part of the room being ventilated and exit of ventilation system is attached directly to that vertical ventilation pipe.

In your case there's a 2,5 meter long horizontal pipe that connects ventilation system's exit in your bathroom with vertical ventilation pipe. Electric fan is used in this case to push air that is being removed from the bathroom through that horizontal pipe to actual ventilation system's exit in your main wall. From that point it is ventilated out naturally.

If we remove electric fan in this case, there's a risk that odour will remain in bathroom and the room itself will be poorly ventilated / won't be ventilated at all.

I won't deny that I am a complete newbie to ventilation systems, so I have absolutely no idea which of these statements is correct or closer to true. Can anyone help here?

  • 2
    It the U.S. a fan is required when there is not a window. This sounds Bizzar to me to remove a vent fan on an interior bathroom, if there is a bathtub/shower my jurisdiction requires the fan to run for 15 minutes after the light is turned off to exhaust all the possible moisture.
    – Ed Beal
    Commented Feb 18, 2020 at 14:34
  • @EdBeal Thank you for your comment. This issue comes from Poland (sorry that I didn't mentioned this). For me, all the concerns are equal to yours: there's a shower in that bathroom and currently electric fan runs, as you said, exactly 15+ minutes after each bath to remove moisture. I have no idea (and management company that issued request for electric fan removal also doesn't have any idea) how after-shower moisture should be removed from no-window bathroom without electric fan.
    – trejder
    Commented Feb 19, 2020 at 9:24

1 Answer 1


I can’t answer for the requirements in your country, but in the mainland United Kingdom, it is now a requirement to have a fixed mains powered ventilation fan in bathrooms and shower rooms regardless where these are in the building. This applies to new builds and in some cases, where renovation takes place.

The whole reason for having a fan is to reduce the humidity in the bathroom or shower room in order to reduce condensation.

The relevant UK regulations are outlined in the ‘Building Regulations Document F

I presume there are similar regulations in your country.

I hope this helps.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, props for taking our tour before posting; few newbies do. Commented Mar 7, 2020 at 12:36

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