DIY Vent Fan Exhaust Duct in Small Bathroom

Mouldy bathrooms are a common problem and unless you find a way to get rid of dampness, moulds will not go away and constant exposure to them can even lead to asthma. The dampness created by hot water (mainly from the shower) ideally needs to be let outside through a duct so that it doesn't stay on ceiling and walls. Ducts are however not standardly made with small fans. Here is a hint how you could make one yourself. You just need to get a bit creative.




I will explain the technical problem right from the start. When you buy a fan with 2 heating bulbs it has a big opening where the damp air is sucked out of the room but there is no connection to a duct.

They look great ...

... but on the other side there is just a a large opening.

This is a small fan with 2 heating bulbs ...

They are made for "leaky" houses where the sucked air is to disappear somewhere through cracks in the walls and roof. But had it been used in a small bathroom, the dampness would stay in the area between your gyprock and the concrete walls above it and effectively come back and condensate slowly destroying your soft wall from the other side.



You need to get the vapours OUT through an opening in the wall that should be in every bathroom.


You need to break the tile with pliers and run the pvc pipe through it

Here it is still untouched

Pipe already in the vent hole. Seal it around it with foam in spray.

The pipe should slightly descend from the fan so that any condensed vapours are led away.

Now you have a duct but how to connect it to the fan?

This is a 100mm pipe but the fan diameter is much larger. I have never found any adapter that would connect the two.

So I took to making one myself.

I needed something that would last and I knew I would have to glue something together. First I had no idea what that something might be and so I was looking for flat plastic containers.

You can see more specs on this picture

The fan is about 240mm high and there not much room left between left between gyprock and the concrete wall above it.

You can best see it on this picture (there is only about 120 mm left):

You're connecting 100mm flexible hose with a much larger opening in the fan

Here is the gypro

 So it had to be fairly flat and it had to be closed and be somehow connected to the 100mm flexible ducting hose or pipe.
First I couldn't find anything that would faintly resemble it. Some tradies couldn't even understand what the heck I was blabbering about. I just couldn't make myself clear enough describing what I wanted.

Then, in desperation I found a fairly flat plastic container in Bunnings. I will update this post as soon as I recall what that was.....

I cut a hole in it and placed it on top of the fan

Here you can see it from the other side

I had to cut a smaller hole on the side and create a matching shape on the pvc pipe. This 'contraption' had to be put together somehow. First I tried to use the industrial sealant (they are of brownish color). But then I spoke to a person who saw that thing after a few years when demolishing bathrooms. They harden and crumble.

Here is what does NOT work

You really do need this one to get the job done

Sikaflex glue is perfect for this purpose. If it's good enough for cars, it will be good enough for fans. It's very strong and lasts for year. When it dries you have a real problem to take things apart.

Anyway, when finally glued together, it looked like this:

It doesn't have to be nice because it will be covered by the gyprock ceiling

As you can see, I covered the top with a plastic sheet and also glued.

There is however a trick. You CANNOT glue the whole thing together FIRST and mount it in the ceiling AFTER because it would not go through the hole in gyprock (that is only slightly larger than the fan diameter).

You have to glue the TOP part FIRST, insert the fan through the gyprock and ONLY THEN glue it together. This is a fiddly work because your access to the ceiling might be very limited.

Here is how it looks when already connected to the duct. No air will leak in between the soft and hard walls and 100% of it goes outside.

 Finally, it has to be connected to power by an electrician.

Here you can already see it connected

With this fan and correctly installed duct you will have no moulds in your bathroom. The ceiling paint will last longer and the bathroom will become a much more hygienic and healthy place. Damp places with moulds can trigger asthma. You can read more on this website that's dedicated to it. Please go and read it carefully. Many people treat consequences but maybe should look at origins first.