Ducting re-jig for shower room extract fan

[FozzieBear]

I have a small ensuite shower room approx. 1.7m square. In the loft above I have a 100mm Manrose MS-100s inline fan connected to a ceiling vent like this

and discharging through the soffit via this

There is a short length of vertical rigid ducting above the inlet spigot and then a 90 degree bend with another 300mm of rigid plastic to which is connected a short length (1.0m) of flexible ducting to join to the fan inlet. The outlet also goes via another short length (1.5m) of flexible ducting to the vent in the soffit. Sketch below

Despite good reviews of the Manrose I am disappointed by the performance. The fan is on its highest speed setting and I have connected a third party timer delay which can run the fan for up to 300 minutes. However, although the fan ceiling valve/inlet is positioned half over the shower and half over the WC it doesn't seem to clear steam and "odours" very quickly.
I've read other posts on this forum and Manrose seems the fan to go to but I am wondering of the flexible ducting is causing too much friction particularly as their is a 180 degree bend in the ducting before enters the fan.
I am wondering if I replaced the inlet side of the fan with rigid plastic ducting and two 90 degree bends where the existing 180 bend is located might reduce the frictional loss. I've got a bit of wiggle room with the fan but a 180 degree bend will have to be incorporated in either the inlet or on the outlet due to access to the soffit.
Am I wasting my time for the benefit It might achieve?
many thanks

 

[HERTS P&D]

You have exactly what i have done, but i connected the fan to a sensor, so when anyone goes into the bathroom or upstairs hallway the fan comes on for 20 mins. Even when the cat goes in the hall it turns it on.

Get a peice of toilet paper and lay it flat on the fan with it on, does the fan hold the paper in place, if so then it is working correctly. You just might need more time.

Andy

 

[endecotp]

How does replacement air enter the room?

 

[mikehammer69]

You have exactly what i have done, but i connected the fan to a sensor, so when anyone goes into the bathroom or upstairs hallway the fan comes on for 20 mins. Even when the cat goes in the hall it turns it on.

Get a peice of toilet paper and lay it flat on the fan with it on, does the fan hold the paper in place, if so then it is working correctly. You just might need more time.

Andy

I've a current relay/ contactor on the shower cable to switch timer fan

Great job the automation, it simply works

Very similar setup to above 1 long straight piece of rigid ducting 2 flexis at inlet and soffit

So that's actually a U bend on the ducting, does that not affect flow and why design it like that rather than more direct ?

 

[Murdochcat]

How big is the gap under the door? Unless the fan can suck air into the room, it can’t blow out

 

[mikehammer69]

Yes the gap ?
Edit : scrap my idea of checking suction with tissue, with that inlet

 

[mikehammer69]

I dunno I'm not an expert on airflow but that looks a terrible design of ductwork

A right angle and a U bend and most of it in flexi not rigid

 

[^woody^]

That length of ducting should not be an issue with a centrifugal fan. What does the fan spec say about duct lengths? Bends tend to count as 1m of duct.

Longer smoother radius would be better than 90°bends.

I can't see why that layout has to be like that. It's that a 2d layout or 3d? If not 3d, could it be? ie take the duct up vertically then bring it down - or ideally out through a tile terminal.

Is there a sufficient door undercut for input air to the bathroom? Min 10mm. Is the door diagonally opposite the ceiling outlet?

 

[FozzieBear]

How does replacement air enter the room?

We cut a large vent in the room door when we refurbished the room for replacement air

 

[FozzieBear]

I've a current relay/ contactor on the shower cable to switch timer fan

Great job the automation, it simply works

Very similar setup to above 1 long straight piece of rigid ducting 2 flexis at inlet and soffit

So that's actually a U bend on the ducting, does that not affect flow and why design it like that rather than more direct ?

I know having a bend is far from ideal but there was no other option. The inlet in the ceiling is close to the external wall where the soffit is so you cant position the fan any other way. Either the 180 bend is on the inlet or the fan is reversed and the bend is on the outlet . That's why I wondered if replacing the 180 with 2 x 90 degree rigid bends might be less resistance??

 

[endecotp]

Is the flexi pipe full of water?

 

[endecotp]

it doesn't seem to clear steam and "odours" very quickly.

Can you quantify that - how quick do you expect it to be?

I have the same (or very similar) inline fan for an en suite. It has about 4 - 5 m of rigid ducting, some 100mm round and some rectangular, and several bends. It does clear the humidity after a shower, but it takes a while; I leave it on for at least 30 mins, often much longer.

 

[FozzieBear]

That length of ducting should not be an issue with a centrifugal fan. What does the fan spec say about duct lengths? Bends tend to count as 1m of duct.

Longer smoother radius would be better than 90°bends.

I can't see why that layout has to be like that. It's that a 2d layout or 3d? If not 3d, could it be? ie take the duct up vertically then bring it down - or ideally out through a tile terminal.

Is there a sufficient door undercut for input air to the bathroom? Min 10mm. Is the door diagonally opposite the ceiling outlet?

Thanks Woody ,see my responses to mikehammer69 and endecotp above re layout and provision for replacement air.

Its far from ideal but best within restrictions available except for perhaps swapping some of the flexible to rigid trunking. I might be able to get a smoother bend using semi rigid aluminium ducting. I could potentially get two larger radius bends using semi rigid but its going to be a b*****d getting it down through the eves.

Manrose specify up to 12m of ducting so well within that.

I hadn't considered a tile vent but that's going to involve a roofer and a specialist tile from Sandtoft their interlocking County Pantiles which are now metric but were imperial when installed 20 plus years ago so new ones don't fit. I've already had that issue with some damage to the verge of my roof which was nightmare to resolve.

 

[FozzieBear]

Is the flexi pipe full of water?

No. No condensation buildup.

 

[FozzieBear]

Can you quantify that - how quick do you expect it to be?

I have the same (or very similar) inline fan for an en suite. It has about 4 - 5 m of rigid ducting, some 100mm round and some rectangular, and several bends. It does clear the humidity after a shower, but it takes a while; I leave it on for at least 30 mins, often much longer.

It can be several hours to clear and I don't have the water very hot.