Extract help.

[number49]

Apologies if this is the wrong section but I'm working on the assumption it's generally sparks that would install extract fans...

I need a bathroom extract which will be installed by our electrician after I've core drilled the hole.

I've been offered a loan of a 117dia core drill to save hiring one, but want to make sure it's the right size as I assumed I'd need something closer to 100mm for a small bathroom extract.

Haven't chosen a specific fan yet but assuming extra low voltage wall fan with trickle and boost.

Can anyone confirm what the usual sizes are and what I line the hole with once it's made???

 

[EFLImpudence]

The fans are usually 100mm and 150mm.

A selection -
http://www.discount-electrical.co.uk/section.php/106104/1/domestic-fans

You can line the hole with any form of ducting or pipe into which the fan will fit and seal with anything suitable.

A hole drilled by a 117mm bit could be alright (although it will end up larger) but on some of the fans the fixing screwholes are too close to the edge of the hole.

A 100mm. (or 150mm) core would be better.

 

[JohnD]

if you use about 110mm, you can poke the duct in fairly loosley, and poke mortar all round to fill the gap. If it useful to fill the cavity with loft insulation stuffed through the hole as soon as you're through the first leaf, not just for insulation but also to prevent fragments falling down it. I don't know why 117mm is so popular. 100mm I have tried but was too tight.

I have small hands and can reach through to push mortar betweeen the duct and the hole in the far side ot the wall. You could probably do it with expanding foam but this will be very messy.

I like to take off the plaster on the inside and pack plenty of mortar round the end of the pipe, so once hard it is strong enough for any fixing screws.

Once the mortar has set, you can slide the duct if necessary, because the mortar will be at a smooth shiny surface where you grouted it hard against the duct.

Give the duct a slight fall to the outside so any condensaton or rain runs out.

 

[trevmai]

A 107mm core bit is normally ok for me.

 

[Lectrician]

Yep, 107mm is ideal (100mm is too tight). 110mm is quite commonly stocked and is fine too. I would be a little worried that a 117mm would be a little too large, the grill and fan not covering the hole, and leaving fixings tricky to drill.

 

[PrenticeBoyofDerry]

I concur with the above two posts, that a 107mm cored hole would be more suitable. If not 110mm is the next best alternative.

 

[number49]

Thanks for the input. Will take the plunge and get hold of a107mm bit instead. I should've mentioned the wall is solid brick so no cavity to worry about (The one and only time my ancient walls are an advantage! )

 

[Lectrician]

A short while ago I had a chap down the road from me come knocking at the door asking if I had a core drill he could borrow. He said he was struggling to get through the wall for his fan and that it was just too hard to keep stitch drilling.

I popped down to his house to get him going with the drill.......

And could immediately see the problem......

He was trying to whack a hole out through the concrete lintel above the window!

 

[PrenticeBoyofDerry]

Thanks for the input. Will take the plunge and get hold of a107mm bit instead. I should've mentioned the wall is solid brick so no cavity to worry about

When coring a hole make sure you use a drill that is suitable for the job, one with an anti lock chuck mechanism, also it is advantageous to do some stitch drilling, can help prevent the core grabbing, also remember to keep pressure on whilst drilling and keep a good grip of the auxiliary handle. This will help prevent any accidents.
Rotation not hammer.
If you don't have the right equipment, it can be hired.