Connecting 40mm pipe to 100mm extractor ducting.

sonny liston

Hi folks,
I have a ground floor bathroom extractor fan that leads up to my attic via a 40mm rigid plastic pipe.
In the attic there is a 100mm flexible ducting which connects to the outside via venting tile on the roof pitch.
Whats the best way to connect the 40mm pipe to the 100mm ducting?

The builder used some black rubber reducer thing("Waterline" is written on it), I have seen them in woodies & b&q. You cut the required width of the smaller hole(32mm or 40mm).

Condensation is collecting inside the rubber reducer and then running down the outside of the 40mm pipe. I was thinking to get a new rubber reducer, and cut a smaller hole to provide a tighter seal with 40mm pipe.

There is also condensation forming where the flexible ducting is placed over the 100mm part of the reducer. The flexible ducting is placed around the outside of rubber reducer and taped together. I think condensation is running down the inside of the ducting, but outside the reducer. I wonder should the ducting be placed inside the reducer so that it contains any condensation that flows back down the ducting?

Of course containing all this condensation means it might run back down the 40mm pipe and damage the fan!

Cheers.

MicktheMan

All ducting, piping etc in the cold attic space needs to be fully insulated all the way to the vent tile. Otherwise you will have a pool of water on your bathroom floor.

DublinDilbert

Is the 40mm pipe circular? Sounds like someone used 1&1/2 waste pipe for the extractor. Is there any chance to upgrade this?

As above you need to insulate all of the ducting very well in the cold attic space

sonny liston

Thanks.
I will look into insulated ducting.

Yes, the 40mm pipe from the fan is circular.

I think the rubber seal the builder used(to connect 40mm pipe up to ducting) is normally used to connect 40mm waste pipe from sink down to larger 100mm sewage pipe?
So, in my case this rubber seal is being used upside down.

Is there a better way for me to connect the pipe up to the ducting?