My previous 2 flats were hotter inside versus outside during summer.

Everyone recommends keeping windows and curtains closed, but it made no difference for me.

I'd assume if my flat was hotter inside than outside, then having my windows open could not hurt. I could never figure out something that worked and my old London flat hit 37.5 Celsius once.

My new flat is on the ground floor at the back of the building in the shade all day and so much cooler. But I on,y have windows on kne side so getting a nice breeze going when I want might not work.

Hit a maximum of 25 in my flat this week thankfully, no fan or aircon.