We’re about to re-do our bathroom and in the planning stages at the minute.

Currently there’s no extractor fan and I’m intending to add one of these.

Currently there’s a 40mm hole in the wall through which old unused water tank overflow pipe is protruding.

Will I be OK to vent out the through this hole or is this likely to kill the fan / not work – i.e. should I then plan to drill out a 100mm hole as per the ducting size?

A follow-up question, assuming I need a larger hole, is it feasible to make the current hole larger or will a new hole be required (I’ve never used a core drill before)?

40mm won’t cut it, go 400mm. Either chain drill or core cut.

Just get some core drill guys to do it. They’ll have it done in half an hour.

Will I be OK to vent out the through this hole or is this likely to kill the fan / not work – i.e. should I then plan to drill out a 100mm hole as per the ducting size?

It won’t work very well because it’s a fraction of the size. Core drills aren’t that hard to use, provided you do it carefully.

The Manrose inline fans are well-rated.

Lol, presume Nobeer meant 100mm.

But yes, drill to the diameter your manufacturer recommends, too big is better in future than too small.

You can core out from 40mm provided its on the edge of the new diameter and there’s enough meat for the pilot drill to hold onto. I’d be inclined to chain drill it though having expanded a 100 to 160 and buggered about with guides to hold it and such. Other option is up into the ceiling space and out the soffit.

Or out thru the slating using a witches hat – thats what I have done and IMO is the easiest way if you have decent access to the roof

+1 for saving yourself some money and going with a Manrose version of the inline extractor you linked. I looked at that vent-axia model when I got my bathroom redone and apart from it being rated slightly quieter I couldn’t see why it cost so much more (shifts slightly less air). From various reviews I read it didn’t seem it was any more reliable than Manrose ones.

If you’re going straight through the wall where are you going to put the inline fan?

Wouldn’t one like this be better?

Aye squirrelking, I meant 100mm, that would give plenty venty!

If you’re going straight through the wall where are you going to put the inline fan?

The current hole is in the loft where the inline fan will go.

+1 for saving yourself some money and going with a Manrose version of the inline extractor you linked. I looked at that vent-axia model when I got my bathroom redone and apart from it being rated slightly quieter I couldn’t see why it cost so much more (shifts slightly less air). From various reviews I read it didn’t seem it was any more reliable than Manrose ones.

Only reason I was choosing the vent-axia one is that it has a 2 year warranty rather than 1 year on the Manrose. Maybe I get conned by this but I take the opinion that if a manufacturer is giving a longer guarantee they are more confident in their product and so chances are it better (tested more?).

As an alternative, we’ve got four of these in the house, 2 running 24/7, 2 on demand only. 2 years so far, no problems.
https://www.greenwood.co.uk/product/153/unity-cv2gip

Manrose timer fan £50 on Ebay. Mine is in the loft and has two intakes going to a Y peice and vented out to a soffit  mounted grill.

A quick related question – we have a manrose fan that vents through our bathroom ceiling through the loft and out of the soffits. It’s only a couple of metres of ducting, but our bathroom is very steamy and in the winter we get a little condensation that drips back through the vent.

This isn’t helped by the hole of the extractor being at the opposite end of the bath to our over-bath shower, but I wondered if I’m likely to see any benefit from swapping the ducting in the loft to insulated duct?

Anecdotal Manrose feedback – we have had our fan for 8 years or so. The original did fail within the warranty period and was replaced with no quibbles. Since then zero issues to report.

I’ve fitted a few, and my main moan is the outlet cover. The flaps to stop birds, insects and vermin getting in make a horrible tap tap tap racket whenever there’s the slightest breeze.
We used to have an Expelair one with a solenoid activated grille but I can’t find one of those.