Extractor with rigid ducting

[jshailes]

Hi. I was wondering if someone could offer any advice regards the installation of an inline bathroom fan please as I'm really not sure sure what to do.

The fan I've purchased is a Vent-Axia ACM125T. The dimensions for the ducting connection is 122mm:

The issue I have is that the rigid ducting is 125mm so it's quite loose. I've considered putting lots of silicone on it, or insulation tape around the axia pipe to make it slightly larger, but both ideas seem a bit of a bodge. I was wondering if anyone could offer advice on the best way to connect it together?

For reference, or in case there's any advice/mistakes I've made, the overall setup is as follows:

Thanks in advance,

Jame

 

[James]

You should use a short length of flexible pipe between duct and fan. Stops vibration down ducting too.

 

[littlespark]

You can get reducers to change from 125 to 100mm if that’s a problem

 

[jshailes]

You can get reducers to change from 125 to 100mm if that’s a problem

Thanks @littlespark, the outlet on the fan is 122mm and the rigid pipe 125mm, so they're quite close, just not sure if they're close enough to just silicone together (or whether silicone is indeed common practice)

 

[jshailes]

You should use a short length of flexible pipe between duct and fan. Stops vibration down ducting too.

OK thanks very much for the tip. It's a pretty short run already, so if I had say 5cm of flexible either side, do you think that would suffice? Am I right in thinking I'd hose clamp the flexible pipe?

 

[littlespark]

Normally, duct is sized to match up with fans and Wall vents etc.... and are different to other 100mm diameters such as drainage pipe.

A cable tie, or a wrap of duct tape is enough to secure.
Hose clamp is a bit overboard unless it’s metal flexi to metal duct. Will crush plastic if overtightened

 

[littlespark]

Ive been asked by another member who has insufficient privileges to post in the DIY section to suggest that the ducting may need a condensation trap.

 

[jshailes]

Ive been asked by another member who has insufficient privileges to post in the DIY section to suggest that the ducting may need a condensation trap.

Thanks. I'd not heard of those until a couple of days ago when I saw someone suggest it on another post - I did a bit of reading and my impression was that a lot of people avoid the need by putting insulation around the ducting. Do you think that's true and if so does it work sufficiently well?

 

[Andy78]

Is the loose fitting verified in practice or just theorised from the data ?

Usually 125mm duct fits a 125mm fan. I'd expect the 122mm to be the internal diameter ?

 

[jshailes]

Is the loose fitting verified in practice or just theorised from the data ?

Yes it's verified. If I put the ducting and fan together on the table and then picked the fan up, then the ducting would fall off. It's not a snug fit, albeit obviously only a small gap, say 1mm or maybe less all the way around it. This is unlike the other fittings I have (pipe connector, vent etc) that fit snugly inside the ducting.