Positioning of extractor fan vent & humidity sensor

as close to the source of the problem as possible. Ideally right by the bog pan. Some people have even plumbed the extract fan to the pan, but that creates a few issues. If no toilet, near the bath/shower.

anywhere except corners, where air doesn't move as much. Ideally in the middle.

right. Although those shutters are far from perfect in windy conditions. Powered shutters are much better.

NT

Agreed, our gravity shutter rattles in windy weather, but we can live with it rather than replace it.

Somewhere you can easily reach it to make adjustments, since you will need to tweak the settings from time to time as the weather changes or if you have a particularly damp few days etc. There is no particular need for the sensor to be in the centre etc.

Its worth having just to stop the external ones clapping open an shut so often in the breeze.

I'll see (or hear or feel) how it goes. I didn't get one with the other stuff, but there's enough room up there to add one later.

Thanks.

Do you put it between the ceiling grate & the fan or between the fan & the outside grate?

the latter.

That's what I would've guessed, but it never hurts to check.

I don't see it making much difference.

NT