Flexible metal ducting for bathroom extraction
- Thread starter morqthana
- Start date
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you need to describe the set up BUT you do not want the vent pipe to be any longer than necessary as it will impair performance
Fully extended , though metal variety not ideal for bathrooms , its cold and promotes condensation , make sure it has a fall to exit point .
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Never seen insulated "concertinard" ducting.
Fully expanded or not, surely the length of the run will be the same?
Well, yes - I had been going to reply to Murdochcat to say that if I stretched it out I would cut it to length, not coil it up.
As for the set-up:
Inline fan in the loft, connected directly to a vent in the bathroom ceiling. One of these, installed vertically:
A metre or so away, horizontally, and less than that vertically, is a vent in the roof tiles.
125mm ducting.
1) Because of the relative distances, I can't use rigid PVC, as 45° elbows won't work, and I've not found adjustable ones. Could possibly use metal, but "125mm" seems to not mean exactly the same thing when mixing systems.
I could switch to using flexible PVC, either the sort sold as ventilation ducting (although that sags more than a baby's nappy way overdue for a change) , or the twinwall underground stuff, which is much more self-supporting, and smooth inside, which would help performance and not trap condensation, but then I might hit the "so what exactly does '125mm' refer to" problem.
2) No chance of a fall to the exit point. Quite the opposite On the outlet side of the fan I have a condensation trap with a pipe draining through the soffit.
I'm going to have to expand the flexi somewhat, or I probably won't be able to get it to bend into the right 'S' shape - I was just wondering if it's advisable to expand it as much as possible.
I guess doing that would mean less weight and therefore less chance of it sagging? I was going to take a view once it's installed as to whether I should create a support for it.
I also wondered, if it were fully expanded, if there'd be less chance of condensation remaining trapped inside it?
Insulation: No, it isn't insulated, and yes I know it should be. But no chance of that happening before winter, so I'm hoping the trap will do its job - I can revisit insulation next year, either wrapping the ducting, or enclosing the whole fan-duct-roof vent space in insulation - Kingspan/Knauf/Celotex PIR boards should do the trick.
Inline fan in the loft, connected directly to a vent in the bathroom ceiling. One of these, installed vertically:
A metre or so away, horizontally, and less than that vertically, is a vent in the roof tiles.
125mm ducting.
1) Because of the relative distances, I can't use rigid PVC, as 45° elbows won't work, and I've not found adjustable ones. Could possibly use metal, but "125mm" seems to not mean exactly the same thing when mixing systems.
I could switch to using flexible PVC, either the sort sold as ventilation ducting (although that sags more than a baby's nappy way overdue for a change) , or the twinwall underground stuff, which is much more self-supporting, and smooth inside, which would help performance and not trap condensation, but then I might hit the "so what exactly does '125mm' refer to" problem.
2) No chance of a fall to the exit point. Quite the opposite On the outlet side of the fan I have a condensation trap with a pipe draining through the soffit.
I'm going to have to expand the flexi somewhat, or I probably won't be able to get it to bend into the right 'S' shape - I was just wondering if it's advisable to expand it as much as possible.
I guess doing that would mean less weight and therefore less chance of it sagging? I was going to take a view once it's installed as to whether I should create a support for it.
I also wondered, if it were fully expanded, if there'd be less chance of condensation remaining trapped inside it?
Insulation: No, it isn't insulated, and yes I know it should be. But no chance of that happening before winter, so I'm hoping the trap will do its job - I can revisit insulation next year, either wrapping the ducting, or enclosing the whole fan-duct-roof vent space in insulation - Kingspan/Knauf/Celotex PIR boards should do the trick.
Annoying though it can be timer overrun is best set as long as possible , this reduces any condensation in pipework.
So cut it to length, support the pipe so it can’t collect condensation in it AND place some loft insulation over it to reduce condensation.
That should be ok. You just don’t want it to have the ability to sag under the weight of an water and effectively block the pipe
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