Extractor fan ducting (condensation)

[drives]

Hi all,

I have an extractor fan in our shower room, directly above the shower cubicle- recently installed a DMEV type fan which all works well in terms of extracting the steam at least. This vents into uninsulated foil ducting, which in turn is attached to a vented tile on the roof.

What I didn't realise was a problem is condensation in the ducting- I've only noticed it the last day or so where the temperature has dropped and it is dripping both back through the fan, and the ceiling where the ducting runs.

I've therefore done some googling today and it would appear that ideally I need to use rigid ducting, and a condensate trap? I don't have much roof space above, due to the dormer roof configuration, and just thought I'd ask for any additional advice on here as to how best to approach it? I was looking at just cutting a section of plasterboard out above the cubicle, doing the above, and then the condensate pipe can go through the soffit/facia?

As said any advice on better (or easier) solutions, or just confirming above appreciated. I suspect my biggest issue is going to be lack of space between the roof tiles and the shower room ceiling, and what is a very short run of ducting. Second photo shows where the dripping is coming through, and last photo is of the roof above (slight pitch over the dormer- vent tile is just underneath left hand velux in the photo. The dormer window to the left is the shower room, and cubicle is against the exterior wall pretty much right below the vent tile).

 

[noseall]

Hi all,

I have an extractor fan in our shower room, directly above the shower cubicle- recently installed a DMEV type fan which all works well in terms of extracting the steam at least. This vents into uninsulated foil ducting, which in turn is attached to a vented tile on the roof.

What I didn't realise was a problem is condensation in the ducting- I've only noticed it the last day or so where the temperature has dropped and it is dripping both back through the fan, and the ceiling where the ducting runs.

I've therefore done some googling today and it would appear that ideally I need to use rigid ducting, and a condensate trap? I don't have much roof space above, due to the dormer roof configuration, and just thought I'd ask for any additional advice on here as to how best to approach it? I was looking at just cutting a section of plasterboard out above the cubicle, doing the above, and then the condensate pipe can go through the soffit/facia?

As said any advice on better (or easier) solutions, or just confirming above appreciated. I suspect my biggest issue is going to be lack of space between the roof tiles and the shower room ceiling, and what is a very short run of ducting. Second photo shows where the dripping is coming through, and last photo is of the roof above (slight pitch over the dormer- vent tile is just underneath left hand velux in the photo. The dormer window to the left is the shower room, and cubicle is against the exterior wall pretty much right below the vent tile).

Have you tried insulating the duct hose?

 

[drives]

Have you tried insulating the duct hose?

No not yet. It looked as though that might be hit and miss as to whether it solves the issue but would certainly be an easier option (albeit I think I’ll still have to cut a chunk out of the ceiling for access).

Having another look this morning I’ve realised the droplets on the ceiling aren’t from a leak above. It’s condensing water where the temperature has dropped, the moisture content in the room is high, and the ceiling isn’t insulated. It’s much worse this morning after I turned the fan off. Will have to have a think about that alongside the drops of water coming back through the fan.

 

[noseall]

No not yet. It looked as though that might be hit and miss as to whether it solves the issue but would certainly be an easier option (albeit I think I’ll still have to cut a chunk out of the ceiling for access).

Having another look this morning I’ve realised the droplets on the ceiling aren’t from a leak above. It’s condensing water where the temperature has dropped, the moisture content in the room is high, and the ceiling isn’t insulated. It’s much worse this morning after I turned the fan off. Will have to have a think about that alongside the drops of water coming back through the fan.

A short duct run, coupled with some insulation wrap, should not cause you any bother. You need to insulate that ceiling. Tack a 50mm PIR board to it, plasterboard and skim.

 

[drives]

A short duct run, coupled with some insulation wrap, should not cause you any bother. You need to insulate that ceiling. Tack a 50mm PIR board to it, plasterboard and skim.

Thanks- Ideally I would pir but it’s just the outer extremities of some of the upstairs rooms where there isn’t any insulation above. The dormer used to be flat roofed and I don’t get when they altered it to pitched why they didn’t insulate above the plasterboard ceiling at that point in these areas, but is what it is…

Edit- attached a photo to show what I have above. The far end is where the soffit vents are. The foam insulation is sitting below the old dormer flat roof. I don't get why they have done what they've done (other than time and money saving obviously but in the grand scheme of things you would have thought sorting this when it was all being constructed would be cost effective). but I didn't want to block the soffit/eaves ventilation by trying to retrospectively push insulation into these gaps?

 

[thomp1983]

Either do as noseall says and add a 50mm PIR board to the underside of your bathroom ceiling then reboard and plaster or,

If it's just that small section shown that's uninsulated cut the current ceiling along the middle of the joist and around the edges and carefully remove it, fit the PIR from below, refit the piece of board you removed then fill and make good the edges before repainting the ceiling.

 

[Murdochcat]

How much of an air gap under the door do you have? For the fan to work effectively it needs to draw dry air into the bathroom from the rest of the house

 

[drives]

How much of an air gap under the door do you have? For the fan to work effectively it needs to draw dry air into the bathroom from the rest of the house

I've got around 4-5mm under the door

 

[thomp1983]

That's not enough, you want at least 10mm on an 800mm wide door for the average 4" extractor fan, we've 15mm under ours.

 

[blup]

A suitable air gap under the door will make a big difference to efficiency

Blup

 

[drives]

Ok thanks I will look at increasing the gap as well

 

[^woody^]

Why is the presence of condensation in the duct a problem?

 

[drives]

Why is the presence of condensation in the duct a problem?

I’m not sure now if it’s collecting in the duct and dripping back down, or just collecting on the outer cover (which is a concave shape on the inner side) as it’s drawing the moist air through.

Either way the issue is it is dripping through the hole for the pir sensor which means it is detecting movement and staying in boost mode until it stops dripping.

 

[drives]

Just wanted to update on this and thank everyone for their help. I fitted insulated ducting (bit of a faff as can’t easily access void) and this has completely solved the problem with respect to water no longer dripping back down through the fan. This was in turn setting off the movement sensor but now this has been sorted the fan works as intended.