The short answer
- A dehumidifier removes water from air. It does not stop water entering the building, and it will not remove mould that has already grown on a surface.
- Aim for indoor relative humidity of roughly 40 to 65 percent. An inexpensive hygrometer, left in 2 or 3 rooms for a fortnight, is the smarter first purchase.
- Run it with the windows and doors of that zone shut, with clearance from walls and curtains. Dehumidifying an open house means dehumidifying Brisbane.
- A neglected unit becomes its own problem: standing water in the tank, a clogged filter and dust on the coils. Clean it on a schedule or do not bother owning one.
- Refrigerant and desiccant units suit different spaces and temperatures. Neither type is simply better than the other.
- If there is an active leak, a dehumidifier only masks it. In the right conditions mould can begin growing in around 48 hours, so drying a water event within hours matters far more than any humidity setpoint.
A dehumidifier is the usual first purchase when a house feels damp, and in the right situation it genuinely helps. It is also sold as the answer to problems it cannot touch. Here is where that line sits, and how to decide whether you need one at all.
What the machine actually does
Air goes in, water comes out of it, drier air goes back into the room. That is the entire function. It has no effect on water coming through a wall, no effect on a slow leak under a vanity, and no effect on a blocked gutter dumping into a cavity.
The part that catches people out is mould that is already there. Drying the air can slow or stall growth, which is worth something. But the growth does not vanish when the humidity drops. It goes quiet. Dormant spores and dead mould still matter, and whether mould is alive was never the measure of whether it is a problem. Removal is physical: a cloth, detergent and effort on non-porous surfaces, and on porous materials the growth extends below what you can see, so the approach depends on the material and the extent. Sometimes the material has to come out. There is more detail on all of this in the guide to mould and damp in Brisbane homes.
A dehumidifier manages air. It does not manage water.
Buy the hygrometer first
Most people buy a machine because the house feels humid. Feel is unreliable, and it is heavily influenced by temperature and by what you were doing 10 minutes earlier. A cheap hygrometer removes the guesswork for a fraction of the cost of a dehumidifier.
Put one in each room you are worried about and leave them for 2 weeks. You are looking for a range of roughly 40 to 65 percent relative humidity, and more importantly for the pattern: what happens overnight in a closed bedroom with 2 people breathing in it, what happens after a shower, what happens on a wet week versus a clear one.
- Keep the hygrometer away from windows, air conditioner outlets and heat sources, at about chest height.
- A room that sits at 55 percent most of the day and spikes to 80 percent for an hour after showers has a ventilation habit to fix, not a machine to buy.
- A room that sits above 70 percent for days at a time is a different conversation, and worth investigating rather than simply drying.
Most of the moisture is generated inside
Brisbane's outdoor humidity gets the blame, and it does contribute. It is not the whole story. Cooking, showering, drying laundry indoors and simply breathing all release water into the house, and a closed-up home with a full clothes rack in the lounge generates its own weather. Several of the highest readings you record will have nothing to do with what is happening outside.
- Run the exhaust fan during showers and for 15 to 20 minutes after, and check that it vents outside rather than into the roof space. Plenty do not.
- Lids on pots. It is a small thing that removes a surprising volume of water from the kitchen air.
- Dry laundry outside where possible. If it has to come inside, put it in one room with the door shut, a fan moving air and an exhaust or open window, rather than spread through the house.
- Open up when the outdoor air is drier than the indoor air, which in practice usually means the middle of a clear afternoon, not 6am.
Sizing, without the marketing
Capacity is quoted in litres per day, measured under warm, very humid test conditions. Your bedroom in August is neither, so real extraction will be lower than the number on the box. Treat the rating as a way of comparing models rather than a promise.
Size for the zone you actually intend to control, not for the floor area of the house. A unit working on a closed bedroom, a laundry or a shut-off living area will hold a setpoint. The same unit in an open-plan house with a stairwell will run continuously, never reach target, and cost you money for a marginal result. Check the tank too. A small tank on a unit running hard means emptying it morning and night, which is why continuous drainage to a laundry tub or floor waste is worth having if it will run for days.
Refrigerant or desiccant
These are 2 different mechanisms. A refrigerant unit chills a coil below the dew point so water condenses out of the air, which works well when the air is warm and loses effectiveness as the space gets colder. A desiccant unit passes air over a moisture-absorbing material and then drives that moisture off with heat, so it holds up better in cooler air and tends to warm the room slightly while it runs.
Which one suits you depends on where it will live and what temperature that space sits at, how much noise and warmth you will tolerate, and what you are running it for. A subfloor or garage in winter and a closed bedroom in February are not the same problem. Anyone who tells you one type is simply better than the other is usually selling that type.
Running it so it earns its power bill
- 1Shut the windows and doors of the zone you are treating. An open house means the unit is working on outdoor air, which it will lose.
- 2Give it clearance. Air needs to get in and out, so keep it away from curtains, walls and the back of the couch, and follow the clearance in the manual.
- 3Set a target inside the 40 to 65 percent band rather than the lowest setting available. Drying a house to 30 percent gains you nothing and is hard on timber and joinery.
- 4Run it when the space is closed. Overnight in a bedroom, or during the day in a shut laundry, usually beats leaving it running in an open living area.
- 5Expect some heat and some noise. Both are normal, and both are worth checking before you put one in a bedroom.
The maintenance nobody mentions at the point of sale
A dehumidifier that is not cleaned turns into a warm, damp, dust-fed box with a fan blowing across it, plugged into the wall of the room you were trying to protect. This is the most common way a good purchase becomes a bad one.
- Empty the tank every day it runs, and wash it properly rather than tipping it out. Standing water at room temperature grows a film quickly.
- Clean or replace the filter at the interval in the manual. A blocked filter drops performance long before you notice it.
- Vacuum dust off the coils and grilles with a brush attachment. Dust plus condensation is exactly the combination we are trying to avoid.
- If you use a drain hose, check it is not kinked and that it is actually draining.
- Before you put it away for the season, run it dry, clean it, and store it somewhere that is not itself damp.
When it is the wrong tool entirely
If water is entering the building, a dehumidifier is a very expensive way to avoid fixing a leak. Set that against the timeline: given the right conditions, mould can begin growing in around 48 hours, so drying a water event within hours rather than days is the single most useful thing anyone can do. A domestic unit alone will not dry a soaked wall cavity or carpet underlay inside that window.
Stop and get the source looked at if you see any of the following.
- Staining that comes back in the same spot after you clean it.
- Bubbling paint, swollen skirting or a soft patch of plasterboard.
- Condensation on the same window every morning while other rooms stay clear.
- A unit that runs constantly and never reaches its setpoint in a closed room.
- Any recent leak, overflow or roof event, whether or not you can still see damage.
Worth saying plainly: this is not an old-house problem. New builds have their own failure modes, including condensation inside steel-framed wall cavities where nothing shows on the surface until it is well advanced. Older stock has its own set, and there is a separate piece on what to watch for in a Queenslander. Neither category is safe by default.
A final point about relying on your senses. Mould does not have to be visible, and it does not have to smell. Most significant problems have no smell at all, and where there is an odour, nose blindness sets in within days of living with it. A house that smells fine is not evidence of anything.
Where cleaning fits into this
Mould needs moisture, food and time. None of the 3 can be eliminated, but all 3 can be influenced. Moisture is the big lever, which is why this article is mostly about water. Housekeeping is the quieter one, and it genuinely counts: dust is food, clutter blocks airflow and holds humidity against surfaces, excess soft furnishings hold moisture, and stacked-up belongings hide the early signs that would otherwise prompt someone to look behind them. Reducing dust and clutter will not fix a leak. It does change how fast a marginal room tips over.
In our own work that means professional HEPA vacuums, the correct brushes, citric acid, steel wool where the surface can take it, and physical effort in place of harsh chemistry. Everything we use is fragrance-free and free from SLS, parabens, phthalates, triclosan, bleach and added dyes, and we leave essential oils out too, because a fragrance is still a fragrance and still a trigger. We clean surface mould where it is safe to do so as part of a clean. We are not remediators, and full remediation is specialist work.
A home health review is a whole-home clean with a careful look at the everyday conditions that hold moisture: airflow, damp-prone corners, and the spots that stay wet after a shower. It is not a mould inspection, a test or a moisture assessment. Where something looks beyond the reach of a clean, we say so, so you know when to bring in a qualified building or mould professional.
On bleach, since it comes up every time: it removes colour while leaving the growth in place on porous surfaces, and it is mostly water, so you are adding moisture to the exact spot you are worried about. It looks like it worked. That is a different thing from working.
Health scope: this article is about buildings, not people. Nothing here diagnoses, treats or gives advice about anyone's health. If you have health concerns relating to your home, speak to your GP or another appropriate health practitioner.
So do they work
Yes, for the job they are built for. A correctly sized, well-placed, well-maintained unit will hold a closed space inside a sensible humidity range, and that is a real advantage in a Brisbane summer, in a laundry, or in a bedroom that runs wet overnight. It is a tool for managing air. Buy the hygrometer first, fix any water source before you spend a cent on a machine, and if you do buy one, commit to cleaning it. If that last part sounds like too much bother, the honest answer is that you are better off without one.
Common questions
What humidity level should I keep my house at in Brisbane?
Roughly 40 to 65 percent relative humidity is the range to aim for. Below that you gain nothing useful and it can be hard on timber and joinery, and sustained readings above it give mould the conditions it needs. The pattern matters as much as the number, so look at what happens overnight in closed bedrooms and after showers, not just the daytime reading in the lounge.
Will a dehumidifier remove mould I can already see?
No. Drying the air can slow or stall further growth, which is worth having, but existing growth does not disappear when humidity drops. It simply goes quiet, and dormant spores and dead mould still matter. Removal is physical: detergent, a cloth and effort on non-porous surfaces, and on porous materials the growth extends below the surface, so the right approach depends on the material and how far it has gone.
Should I run a dehumidifier with the windows open?
No. With windows or external doors open the unit is effectively trying to dry outdoor air, which it will never win. Close the room or zone you are treating, give the unit clearance from walls, curtains and furniture, and let it work on a defined space. Ventilation is still valuable, just not at the same time as the dehumidifier.
Do I need a dehumidifier or an air purifier?
They do different jobs. A dehumidifier removes water from the air and changes the conditions mould needs. An air purifier filters particles out of the air but does nothing about moisture, so it will not change those underlying conditions. If your humidity readings sit high, the dehumidifier is the relevant tool. If your readings are fine, a purifier will not fix a damp problem you have not found yet.
Is a refrigerant or a desiccant dehumidifier better?
Neither is better in general. A refrigerant unit condenses water on a chilled coil and works best in warm air, losing effectiveness as the space gets colder. A desiccant unit absorbs moisture and drives it off with heat, so it copes better in cooler spaces and warms the room slightly while it runs. The right choice depends on the temperature of the space, the noise and warmth you will tolerate, and what you are running it for.
How often does a dehumidifier need cleaning?
Empty and wash the tank every day it runs rather than just tipping it out, clean or replace the filter at the interval given in the manual, and vacuum dust off the coils and grilles regularly. A neglected unit holds standing water and dust in a warm space with a fan blowing across it, which is exactly the condition you bought it to avoid. Run it dry and clean it before storing it between seasons.
Is a dehumidifier enough after a leak or flood?
Not on its own. Given the right conditions mould can begin growing in around 48 hours, so drying within hours rather than days is what counts, and a domestic dehumidifier will not dry a soaked wall cavity or carpet underlay inside that window. Stop the water source, get the wet materials dealt with properly, and treat the dehumidifier as one part of the drying effort rather than the whole plan.