Where does the shower steam actually go?
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We run the ensuite fan for every shower, and I have wondered where it blows. Last week I took a torch up through the manhole to find out.
It does not go outside. There is no duct at all. The fan is part of the combined heat lamp, light and exhaust unit in the ceiling, and it discharges straight up into the roof space. So does the one in the loft bathroom, an older unit doing the same thing, but I think into a tighter roof space.
Up there it is timber, insulation and still air, and in winter it is colder than any room below. Every shower we have taken in this house has sent its steam to the coldest, least ventilated part of the building, several times a day, for years.
Fixing it properly is not simply a matter of running a pipe out to the eave. The cheap axial fan fitted in most Australian ceilings moves plenty of air with nothing attached to it, and far less once it has to push through a duct — so the fan has to be able to shift air through the pipe as well.
The Australian Government's YourHome guide is blunt about the principle: vent bathroom, laundry and kitchen exhaust directly outdoors. Ours do not.
What I do not know is how much this has cost us. I could see no mould on the underside of the roof while I was up there, which is the good news, and you can judge that from the photos as well as I can.
Is it worth getting both of them ducted outside? For now the ensuite window does more than the fan does.
Coming up
Machine versus open window: which one earns its electricity.
The leak we found under the vanity.
Saving the bed slats.
Related Posts
- Previous — wet windows, and the tool that turns them into a dehumidifier: Wet windows: the free dehumidifier 7 Aug 2026
- Earlier — why our heating leaves the moisture in: Our heating doesn't breathe 3 Aug 2026
Links
- On choosing a bathroom fan — why a cheap axial fan moves far less air once it has to push through a duct: What bathroom fan should you use and not use? — Efficiency Matrix
- The Australian Government on condensation, including venting exhaust fans outdoors: YourHome — Condensation
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No mound in Canberra climate and was still practice in 2012
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Should be vented external to the house.
That looks perfect for growing mould.
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I can honestly say I have never seen mould in a ceiling caused by bathroom fans.
Having said that, they have always been older homes where the roof space has lots of natural ventilation.
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Conditioned space ends at the ceiling. Exhaust warm air full of moisture , it condenses on the cold tin, grows mould as the tin warms air rises picks up the water and the mould carries it out the top, spills over mould grows in the nice warm air full of water in the sun...
Mould, mould and more mould
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In any case those fixtures can go.
Very dated now big hole = loosing heaps of heat all the time like a big chimney.
Stick your head over it in the roof space with fan off see what I mean
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Also, the first combination bathroom fans and lights we bought were hopeless even though they were supposedly designed to be used with venting. All up I think we spent around $1,000 mainly on decent fans.
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Given how poorly insulated your ceiling is, I’d fix that as a priority first.
Yes, ducting to outdoors is better, and should be considered for sure. A whirly bird or two can also assist.
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They are fine, it's nothing to worry about.
However, my rangehood is ducted up to the whirly wind.
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Personally I think we are still in the "limbo 1/2 way" solution to building and dealing with nothing humidty & temperature but we are getting there
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Our ceiling was the same, and when I was younger (and still had joints that actually move) I fixed it all, making it do a much better job.
Our bathroom exhaust fans (x2) are the same. I’ve never seen any issue, as the roof space is naturally quite well ventilated with gaps around the edge etc.
We’re in SEQ though with a somewhat different climate. Summer heat is our problem, not winter cold. What helped with that REALLY DRAMATICALLY was in 2012 when we ripped the old dark 1970 tiles off and fitted “Surfmist” colorbond, complete with good blanket insulation under the colorbond.
That made an absolutely MASSIVE difference to our Summer cooling.
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Colourbond or tiled with sarking = duct it outside with proper inline fan to have enough grunt to push the air out.
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We added a solar powered roof ventilator, it has a solar panel on the top side which runs a small fan in sunlight hours.
All our bathroom fans we have vented to eaves/verandah ceiling or through the roof tiles. We have one old fan in our hallway loo that vents into the roof space - but it only extracts filthy smells (LoL) not steam.
A product we got recently from Bunnings (but it may have been discontinued on Clearance) is a low profile roof vent - it has a wide flashing and the vent part looks like a tortoise shell. It's vented on the downslope side and includes strong mesh grille to prevent insect entry and possibly bushfire embers. It sits very low to the roof tiles and looks unobtrusive. On bbq rangehoods venting through the verandah roof tiles we used stainless flues and cowls, hoping that any grease would vent to air not so much on the roof.
In our newer fans, we used the stiff corrugated aluminium ducts. The floppy silver foil type ducts included with budget fans have much worse airflow characteristics.
It is easy to get fan units with side ducted air outlets. Many fans give stats of airflow on the box and in general a larger duct gives better airflow - so choose 150mm or 125mm duct versions over a 100mm duct version.
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