Dehumidifier for Mould

Does a dehumidifier help with mould?

Yes, and the reason comes down to one number: humidity. Mould spores are floating in the air of every home, all the time. They are harmless until they land somewhere damp and start to grow. Mould generally needs relative humidity above 60 percent to take hold. Keep the air drier than that and the spores simply cannot get going.

A dehumidifier pulls moist air in, strips the water out of it, and returns drier air to the room. Run consistently, it holds the humidity in a problem area down in the safe zone, which is roughly 30 to 50 percent. That is below the level mould needs, so existing growth is starved and new growth is prevented.

What a dehumidifier will not do is remove mould that has already established itself. If you can see it or smell it, that colony needs to be physically treated and removed first. The dehumidifier then does the long term job of keeping the conditions wrong for mould to return.

What humidity level stops mould?

Aim to keep indoor relative humidity between 30 and 50 percent. Once you climb past 60 percent, you are in mould territory. The table below is a quick guide to what different humidity levels mean inside the home.

A cheap hygrometer (a humidity meter) from a hardware store lets you see where your rooms actually sit. Most people are surprised how high the reading climbs in winter, when windows stay shut and warm moist air has nowhere to go.

Where dehumidifiers make the biggest difference

Some spaces in an Australian home trap moisture far more than others. These are the spots where a dehumidifier tends to pay off fastest:

• Bedrooms and living areas in winter, when condensation forms on cold windows overnight.
• Wardrobes and built-in robes, where still air and packed clothing hold dampness.
• Bathrooms and laundries that lack an exhaust fan or get little natural light.
• Basements, garages and under-house storage that sit cool and poorly ventilated.
• Rooms on the shady, south facing side of the house that never quite dry out.
• Homes near the coast or in high rainfall areas where outdoor humidity stays up most of the year.

Compressor or desiccant: which type of dehumidifier is best for mould?

There are two main types, and the right choice depends mostly on how cool the room gets. This matters more in Australia than people expect, because the rooms with the worst mould are often the coldest ones.

Compressor (refrigerant) dehumidifiers

These chill a coil so moisture condenses out of the air, much like the back of a fridge. They are efficient in warm, humid conditions, which makes them a solid pick for summer dampness and for warmer parts of the country. Their weakness is the cold. As the room temperature drops below about 15 degrees, they lose efficiency, which is a problem because winter is when many homes get their worst mould.

Desiccant dehumidifiers

These use a moisture absorbing material rather than a cold coil, so they keep working effectively even in cool rooms. For the typical Australian mould problem, a bedroom, wardrobe or bathroom that turns damp and cold through winter, a desiccant unit is usually the better all round choice. They also tend to run more quietly, which matters in a bedroom.
For most homes dealing with recurring mould, we recommend a desiccant dehumidifier. It handles the cold, damp conditions that cause the majority of the call outs we see.

How to choose the right size

Dehumidifiers are rated by how many litres of water they can pull from the air in a day. Bigger is not always better; you want a unit matched to the space so it runs efficiently without short cycling. As a rough guide:

• A single bedroom, wardrobe or small bathroom is well covered by a 10 to 12 litre unit.
• An open plan living area or several connected rooms suits a 20 to 25 litre unit.
• A whole floor, a damp basement or a large area after water damage calls for a 30 litre unit or larger.

Look for a model with a built in humidistat. This lets you set a target humidity, say 50 percent, and the unit switches itself on and off to hold that level. You get the protection without the power bill of running it around the clock.

Our recommended dehumidifiers

We only stock units we are happy to put our name behind, chosen for Australian conditions and the kind of mould problems we treat every day. Each comes with a smart humidistat so it manages itself once you set your target level.

• Cool-Seasons 10L Smart Desiccant Dehumidifier: ideal for a bedroom, wardrobe or bathroom, and well suited to cool winter conditions.
• Large 35L Smart Dehumidifier: built for bigger areas, open plan homes, or drying out a space after a leak or flood.

You can see current pricing and order directly from our online shop, or ask our team which size fits your situation.

A dehumidifier is part of the solution, not the whole fix

It is worth being clear about this, because it saves people money and frustration. A dehumidifier manages the symptom, which is damp air. It does not address the source of that moisture. If mould keeps returning, something is feeding it: a hidden leak, poor ventilation, rising damp, condensation from a structural cold spot, or a bathroom with no working exhaust fan.

The most reliable way to beat mould for good is a three step approach. First, find and fix the moisture source. Second, professionally remove the existing mould so spores are not left to spread. Third, control the humidity going forward with proper ventilation and, where needed, a dehumidifier. Skip the first two steps and you will be running that dehumidifier forever while the mould quietly carries on behind the scenes.

Not sure where your moisture is coming from?

This is the part most homeowners cannot diagnose on their own, and it is exactly what we do. The Mould Doctor provides a free inspection for properties with visible mould across Victoria, New South Wales and South East Queensland. Our technician takes moisture and humidity readings, identifies what is actually causing the problem, and gives you a clear report with recommendations and a quote. Every treatment is backed by our 12 month guarantee.

Call 1300 944 595 or request a quote online to get started.

Frequently asked questions

Will a dehumidifier remove mould that is already on the wall?

No. A dehumidifier dries the air and stops mould spreading, but it cannot remove an existing colony. Visible mould needs to be physically treated and removed first. The dehumidifier then keeps conditions dry so it does not come back.

How long should I run a dehumidifier each day?

With a built in humidistat you can simply set your target humidity, around 50 percent, and let the unit decide. It will run when the air gets damp and rest when it does not. In a badly affected room you may run it most of the day at first, then far less once the space dries out.

Does a dehumidifier work better than opening windows?

It depends on the outside air. On a dry, breezy day, opening windows is free and effective. But in winter, in wet weather, or in humid coastal areas, the outside air is often damper than the inside, so airing out the room can make things worse. A dehumidifier works regardless of the weather outside.

What size dehumidifier do I need for mould?

For a single bedroom, wardrobe or bathroom, a 10 to 12 litre unit is plenty. For open plan living areas choose 20 to 25 litres, and for whole floors, basements or flood recovery go for 30 litres or more. Matching the size to the space keeps it efficient.

Are dehumidifiers expensive to run?

Less than most people fear, especially a desiccant model with a humidistat. Because it only runs when humidity climbs above your set point, it is not drawing power constantly. The cost is small compared with repeated mould treatments or the damage damp does to a home over time.