Where Does Your Dryer Actually Vent? Why a Roof or Wall Cavity Is the Wrong Answer

A vented dryer does one thing that people rarely think about: it takes the water out of a load of wet washing and puts it into the air. A full load holds a genuinely surprising amount of water, and all of it has to go somewhere. That is the whole job.

Which makes the important question about any dryer not how well it dries, but where that air ends up. In a lot of Melbourne homes — particularly townhouses, apartments, converted laundries and any house where the laundry has been moved during a renovation — the honest answer is that nobody knows, and the duct does not reach outside at all.

What a dryer is actually discharging

Warm, saturated air, plus lint. Over a winter of daily loads, that is a large volume of water leaving the machine, week after week, in a season when the house is shut up and nothing else is drying out either.

Discharged outside, this is unremarkable. It leaves the building and disperses. Discharged anywhere inside the building fabric, it becomes the single most concentrated moisture source in the house, running several times a week into a space with no ventilation and no sunlight.

The three terminations we find

There are effectively three ways a dryer duct ends, and only one of them is correct.

Through the wall or eave to an external hood. The right answer. A short rigid run to a proper external termination with a flap that opens under airflow and closes when the machine stops.

Into the roof space or a wall cavity. Extremely common in retrofits. Somebody ran a flexible hose up through the ceiling with every intention of taking it out through the eave, and it never happened. The duct discharges into the roof cavity and the laundry seems fine, because from inside the room the dryer is behaving normally.

Nowhere at all. The hose has fallen off the back of the machine, or was never connected, or has split behind the appliance. The dryer vents straight into the laundry. This one at least announces itself: the room fogs up, the walls run with condensation, and the door has to be left open.

What venting into a cavity does over a winter

A roof cavity has no way to shed water. Warm wet air rises into it, meets the cold underside of the roof on a Melbourne winter night, and condenses. That water runs down onto the ceiling insulation and the framing, and it does this again every time the dryer runs.

Meanwhile the lint that would normally leave the building settles across everything up there, holding moisture in place and adding a fuel load in a space nobody inspects.

The damage shows up in a way that rarely gets connected back to the dryer. Insulation compresses, gets damp and stops insulating properly. Ceiling plaster stains or sags. A musty smell appears in a bedroom or a wardrobe that shares a wall or ceiling with the laundry. Mould grows on the cold side of a ceiling, sometimes appearing metres away from where the duct actually ends. People clean the mould, it comes back, and the machine that is causing it keeps running three times a week.

A wall cavity is the same problem in a narrower space, with the added issue that the moisture is now inside a wall where it can reach framing and insulation directly.

How to trace your own duct in ten minutes

This is genuinely worth doing, and it takes very little.

Start at the machine. Pull it out far enough to see the back and confirm the duct is actually attached, not lying on the floor behind it. Follow the duct as far as you can see. Note whether it goes through an external wall, disappears up into the ceiling, or vanishes into a cupboard or cavity.

Then go outside while the dryer is running on a warm cycle. Look for a hood on the wall or under the eave on that side of the house. If it exists, you should feel warm damp air and see the flap lifting. Nothing moving, or no hood at all, means the air is going somewhere inside.

Two other signals worth trusting. If the laundry itself fogs up while the dryer runs, the duct is disconnected or split. And if a room adjacent to or above the laundry has developed a musty smell or a stain on the ceiling over winter, treat that as evidence about the duct rather than a coincidence.

What a proper run looks like

Short and straight, to the nearest external wall or eave. Every extra metre and every bend costs airflow, and lost airflow is why lint settles inside a duct rather than leaving through it.

Rigid or semi-rigid smooth ducting is far better than a long length of concertina hose. The ribs inside flexible hose catch lint at every corrugation, and a hose left slack behind the machine develops a sag that collects condensate and eventually blocks solid.

The termination needs a hood with a functioning flap. Not an open pipe end, which lets weather, insects and birds straight back in, and not a mesh screen, which lint blinds off within months. And the run has to stay clear, which is what dryer vent cleaning exists to do — a blocked duct is both a fire risk and, for the purposes of this article, a duct that is now discharging its moisture backwards into the room.

If there is no route to an external wall

Plenty of Melbourne laundries are internal, in the middle of an apartment or tucked into a hallway cupboard, with no practical path outside. Venting into the ceiling because it is the only option available is still not an option; it simply moves the damage out of sight.

The two real answers are a properly ducted run to whatever external wall can be reached, even if it takes a route through a cupboard, or a condenser or heat pump dryer, which does not vent at all and collects the water instead. Heat pump models also tend to run cooler and are worth looking at on their own merits.

Whichever way it goes, the principle does not change. The water in a load of washing has to leave the building. Any arrangement that stops short of that is not drying the clothes so much as relocating the problem into a part of the house nobody looks at until something stains.

Frequently asked questions

How can I tell whether my dryer vents outside?

Run the dryer on a warm cycle and go outside to the wall or eave where you expect the vent to be. A working termination has a hood with a flap that lifts, and you will feel warm damp air and see the flap moving. If you cannot find a hood anywhere on that side of the house, the duct almost certainly ends somewhere inside the building fabric.

Is it really a problem if the duct just ends in the roof space?

Yes, and it is a slow one rather than an obvious one. A roof cavity has no mechanism for shedding water. The moisture from every load condenses on the cold underside of the roof overnight, drips onto insulation and framing, and lint settles on top of it all. The visible result is usually staining or mould on a ceiling, sagging insulation, or a musty smell in a nearby wardrobe.

Can a duct be too long or have too many bends?

It can. Every extra metre and every bend adds resistance, so the fan moves less air, the cycle runs longer, and lint drops out of the airflow inside the duct instead of leaving with it. The best run is the shortest, straightest one to the nearest external wall, using smooth rigid ducting rather than a long loop of concertina hose.

Do condenser and heat pump dryers need a duct at all?

No, and that is the point of them. They condense the moisture and collect it in a tank or send it out through a drain, so nothing needs to be ducted anywhere. They are worth considering in an apartment or an internal laundry where there is no practical route to an external wall — but the water still has to be emptied or plumbed, and their lint filters still need clearing every cycle.