I have a bathroom 2.5m X 1.8m X 3.5m ceiling. On one wall at 2.4m off the ground there is approximately 0.9m X 0.4m ventilation frame, which is covered in metal mosquito mesh. There is a further 0.8 X 0.2m mesh lower down the same wall, obscured by wooden slats, and another on the side wall (both open to outside). There is a further mesh of 0.9m X 0.3m above the door to the rest of the house, which is opposite the 0.9x0.4m mesh

The outside weather is constantly 22-30C and the room will never be air conditioned.

Humidity is normally around 90% but ranges between 80 and 100%. There is very little natural breezes.

I have a 75 m^3/hour flow extractor fan which I can fit, but I'm not sure if it will do anything in that presumably the room is experiencing air changes already due to the meshed openings.

To be clear I'm not experiencing any particular issues that I want to address, but I'm demolishing part of the wall, so could install the fan, but do not have to.

Edit: added photo of top part of wall being rebuilt.enter image description here mesh currently removed.

  • Install it in one of the openings. But not the one obscured by slats .
    – Solar Mike
    Commented Jun 12, 2021 at 6:39
  • that part of the wall is being knocked down and rebuilt. So I can add the fan to the existing opening, or make a new opening, it doesn't make a difference either way.. photo added....
    – thelawnet
    Commented Jun 12, 2021 at 7:08

2 Answers 2


If you place an extractor fan near a natural opening you will create what is referred to as a "short-circuit", where air from the adjacent natural opening will be pulled into the fan and ejected. This setup will likely do little to move air in the rest of the space:

enter image description here

If you can place the fan in a wall away from/opposite the natural opening, you will then provide some air movement across the space:

enter image description here


Will it increase airflow?

Yes. Fan forced ventilation does that, even with natural ventilation happening at the same time. It also directs the airflow that it causes out of the house (relevant since you have a ventilation opening into the house.)

Do you need it, given large natural ventilation openings?

Seems likely not, given that you are not experiencing problems as it stands. But if you'd like to put it in, since you have it, you always have the option of not running it - perhaps it will have some benefit, some times, given the lack of natural breezes.

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