I’d like to drill two 4 inch holes in this wall.
It’s a supporting wall and 4 inches thick.
They would be centred 40 cm from the ceiling and 40 cm from the wall.
Will I and the 3 flats above die?
Would one 6 inch hole 60cm from wall be stronger and offer better airflow?
.

proper diamond core drill

http://www.diydoctor.org.uk/projects/core-drill.htm

get costs from a company to do, time you hire tools and time taken by you the price difference might not be worth the hassle DIY.

No one will die as a result of your holes. Four inch is a common size for soil pipes but the bigger the hole the harder to drill assuming you will be using a core bit. What is the wall made of? Is this in Hatton Garden?

If you pull that Mitsubishi thing off the wall, there might be some holes there already.

price difference might not be worth the hassle DIY.

Is a fair point. Any plumber should have the tools but probably won’t fancy the job

I certainly won’t be doing it!
If the idea is sound then I shall get someone in to quote.

It’s not worth the hassle. I’m working at stuff like this daily. Get a quote from a guy that does core drilling, much quicker and easier.

Crack on:

😆

Tell the freeholder before you do it.

This is a seriousish alteration.

It will be dusty and make a nice mess

Your aircon unit will be under spec for the new volume to be cooled/heated. Look forward to a whole world of fun with either too hot or too cold days.

Holes will be able to be closed.
The reason for the holes is that our chocolate cabinet is tucked away in a corner. An absolute gale blows through our back door completely missing the chocolate corner. This will stop us having to put on the air con on all but the hottest days.
Would 3 holes be safe? From the unit to the wall is 120cm.

“…the 3 flats above…“

You may find that it’s not your wall to be drilling. As above, get permission.