Bathroom ventilation opening

[svouts]

Hi, I need to open a ventilation hole in the wall of my bathroom to install a 4 inch ventilation fun. Structurally, since it is an external load bearing wall, what is the best place to make the opening?
Shall I do it above the window or in the corner? I attach a picture with the two options highlighted:
-red circle above the window
-green circle towards the corner
-any other thoughts?
I basically look for the more structurally sound place for the opening.

 

[JohnD]

please show the outside wall.

if it is a gable with little brickwork above, it may be better to avoid the corner.

water vapour is lighter than air and rises to the ceiling, so the higher your fan, the better

Are you putting it above the bath or shower?

What is the ceiling height above the floor?

 

[svouts]

here are some pictures form the inside showing all the window and form the outside.

above there is another floor, with wooden joists.

The bathroom is in the other corner, but this corner it is closer to a wall with electricity and there are cabinets to hide the electric cables.

The ceiling has 3meters or about 10 feet height.

 

[JohnD]

then the wall will be rigid enough

put it close to the ceiling

it looks like above you is another flat, so you will not want anything too noisy or intruding through the ceiling. If theirs is a bathroom, and/or they have a concrete floor, noise will not be such a nuisance.

Modern extractors with ball-bearing motors can be surprisingly quiet

A 4-inch/100mm fan is usually the minimum, and is adequate for a bathroom or WC, but not if you have steamy showers. They usually are rated at about 80 cu.m/hr. I recommend you have it wired to the ceiling light, with a run-on time delay. ("T" for "timed")

If you only get a 100mm, you may have to run it for long periods to keep the bathroom free of condensation. It looks like you have solid 9" brick walls, which will be cold in winter.

You can get a 125mm or 150mm fan that will be substantially more powerful. You are going to have to core a hole through the wall anyway so you may as well do a big one.

If you get one with a noise rating of 25db, that is pretty quiet.

Some are available with speed control at much higher cost.

Soler & Palau make the best ones I've seen, but some of their identical models are branded Envirovent which is the UK subsidiary, and often at lower prices. Read the tech spec to ensure the motor is mounted on flexible rubber pads, and has ball-bearings (other, similar-looking makers do not have these features and their fans are not as quiet). I have also used Airflow, which are not quite as good, and Manrose, which are much worse.

Here are a few examples. Look at air throughput, in cubic metres per hour, and sound, in db

100mm

125mm

150mm

You can get ducted ones that are even better, but they are usually fitted in a loft or false ceiling, being bigger.

 

[RandomGrinch]

If you are considering doing the core drilling yourself, stick to the 4" and get yourself a work platform for the outside (it's far neater to drill from both sides).
Also make sure the drill is a tough SDS, with a clutch and take your time!
Anything more than 4" would definitely be a job for a pro.

 

[^woody^]

Typically, room fans should where possible be placed 3/4 of the room height, 300mm in from any corner, and diagonally opposite/furthest corner away from the entrance door to the room