How do I form a seal between these please

[denso13]

It is, you have a standard set up, nothing overly long at all. A slight slope to the grill will deal with any water build up.

 

[Jupiter01]

It is, you have a standard set up, nothing overly long at all. A slight slope to the grill will deal with any water build up.

the manrose pipe coming out of the fan is around 1.5 metres long. This then goes into the vertical pipe which is around 1.5m.

 

[denso13]

3m through an inline duct in a loft is pretty average. Simply sloping it back the way, which costs nothing, should solve it, if not you can look at other solutions.

Again, I have never seen something of this length done in soil pipe.

 

[Madrab]

Maybe it's just me but I wouldn't want condensate dripping out of a roof vent onto the bathroom floor TBTH, if that's the idea/outcome

 

[potterton678]

I was thinking something like this?
View attachment 413273

This setup will always collect water somewhere. Insulation will help but it won't eliminate the problem. Ideally, you need the exhaust vent to be in a gable end wall. Can you do that?

 

[JohnD]

3m through an inline duct in a loft is pretty average. Simply sloping it back the way, which costs nothing, should solve it, if not you can look at other solutions.

Again, I have never seen something of this length done in soil pipe.

I used to use soil pipe, which is readily available in long lengths, with fittings, and very sturdy, but, annoyingly, some brands of fan now have spigots that will not fit inside it. You can buy rigid duct from HVAC suppliers, including insulated versions.

I really don't like the convoluted flexi pipe.

I agree about running it horizontally (with a slight fall to the outside) if you can. The initial length will be the warmest and least prone to condensation.