New Bathroom Fan

[imroberts]

I've just moved into a house which doesn't currently have a bathroom fan.

I think I've decided on a Vent Axia ACM100T as it looks to have a high airflow as well as being one of the quietest available. Though if you think there are better units out there please let me know.

I have a number of questions about the best way to install it:

1) I like this kind of vent from an aesthetic point of view. Is there any issue using something like this or will this be fine?
https://www.amazon.co.uk/gp/product/B004X4RKL6/

2) I imagine I'll install the fan with flexible PVC ducting. Is there a significant benefit to the flexible aluminium stuff or to using solid ducting instead?

3) In terms of back draught shutters, what's best? My experience of gravity flaps is they tend to rattle in the wind so I'd wondered whether an in line back draught shutter was a better option? If I go with this as an option, are any better than the others? Where should it go relative to the outside and to the fan unit? What type of external grille should be fitted alongside an in line shutter?

Any other advice anyone can offer would be appreciated.

 

[JohnD]

I find a cowl vent is good for weather resistance and not rattling much. Some of the better fans have built-in non-return valves like butterfly wings in very thin light plastic.

Rigid duct is much better than flexible hose. It does not trap so much dust and fluff and can easily be wiped clean. Tilt it slightly so any condensation runs outside and can't collect in the duct (flexy is bad for that too). Wrap loft insulation round the duct to minimise condensation and muffle sound.

Soler & Palau make very good quality fans, including some that have been sold branded as vent-axia

Examples
https://www.tlc-direct.co.uk/Products/SLTD250.html
https://www.tlc-direct.co.uk/Products/SLTD160T.html

They also make some 5-inch and bigger ones, which will be quieter as they can run slower., and the bigger duct allows better airflow

You will find one-way valves and other accessories via my link.

Check throughput, noise, and price inc vat when comparing.

If you get a 2-speed one you can try it at the quieter low speed and see if that is sufficient (remote speed change controls are surprisingly expensive but you can do it at installation wiring connection).

 

[imroberts]

If rigid ducting is better I'll go with that - it's only a shortish run so the costs aren't prohibitive - though the elbows are more costly than I imagined!

Does rigid ducting need joining with solvent cement or anything, or does it simply push together?

Tilting to channel any moisture outside makes sense - should I also tilt the ducting *before* the fan slightly to channel any water outside (albeit via the fan) or should I tilt this the other way to channel any moisture back into the bathroom? The latter seems a little counter-intuitive but wanted to be sure what was best.

 

[JohnD]

You don't want water trying to run into the fan.

the pipe adjacent to the fan will be the warmest part. Wrap it in insulation. Presumably it will be quite short so not much condensation anyway. You can let it tilt towards the bathroom (not dripping onto the ceiling). If you actually get water dripping out of it (unlikely) you can add a duct drain.

I confess I don't use cement on my ducts. with a bit of slope on it, any water should run into the socket and away. but in my case the fan runs every time the room is used and I don't get discernable condensation. If you have lots of steamy showers maybe you will.

flexy hose is bad for condensation because it tends to drape in loops and water collects at the bottom of each loop

 

[imroberts]

Thanks for the advice. Next question is around hole sizes!

I have, if memory serves me right, a 107mm core drill which I thought I'd used for installing a 4" vent at a previous property. I was in B&Q today and all their 4" ducting recommended a hole of at least 112mm... I'd like the holes to be as tight as possible and, ideally, I'd rather not buy a new core drill just for this job, but if I need to, I need to.

Firstly, is a 107mm core drill fine for the cavity wall? What would be the "normal" size people would drill?

Secondly, I've cut ceilings with a padsaw before now but I'm going to get a holesaw for this job as the bathroom is recently decorated and I want to avoid any possibility of damage. I see a common size for holesaws is 102mm - given a 4" / 100mm vent should be that size I assume, I'd have thought a 102mm hole would suffice? Again what would be the norm?