Does A Dehumidifier Help With Mold?

Nobody wants to find mold growing in their home or property, it’s unsightly, it smells and it can be hazardous to people’s health.

You may have heard that buying and running a dehumidifier will help stop mold growth, but does it kill it, and how can you tell if it’s actually working?

In this article, we will be answering all these questions and many more, so for everything you need to know about dehumidifiers and mold growth, keep reading.

Dehumidifiers assist in both the prevention and removal of mold, by decreasing the overall moisture levels in a room to the point where it either cannot grow in the first place or, will dry out, become dormant, and be far easier to remove. They will not kill mold, but can certainly help prevent it.

Can a dehumidifier help with mold

What does a dehumidifier do?

A dehumidifier does exactly what you would expect from its name, it removes moisture from the air until the relative humidity reaches the percentage set by the user.

Refrigeration dehumidifiers work by drawing moisture-laden air into the unit via a grille. It is then passed over cooled pipes where the moisture condensates, and drips down into a reservoir where it can be collected. The warm and dry air is then passed back out of the unit into the room.

Absorption dehumidifiers are seen less often, and function in an entirely different way.

Again, moisture-laden air is drawn into the unit via an electric fan. It is then passed over a rotating wheel made of absorbent material that then has hot air blown on it to dry it out. The water evaporates from the absorbent material and is sent down an exhaust pipe to be redistributed.

How to tell if you need a dehumidifier

Living in heavily insulated properties has somewhat acclimatized us to living in a high-humidity environment. Here are some of the telltale signs that you may be living with excessively high humidity levels that need addressing.

Wall sweating

One of the easiest ways to tell if you might need to make use of a dehumidifier is to check your walls for moisture. A concrete wall is often cooler than partition walls, so this is where moisture will most likely begin to condensate (referred to as “sweating”).

If you can see obvious signs of water condensing on any of the walls in your property, it is a sure signal that you are dealing with very high levels of humidity that a dehumidifier could certainly help with.

Window fog

Check your windows throughout the day to see if they have become foggy or if any small droplets of water have developed.

Moisture will condensate on a window pane, as it is often several degrees cooler than the internal temperature of the room it is placed in.

Mold development

This of course is the main topic of this article, so if you have discovered mold growing in any room of a property, then it almost certainly has high humidity levels.

Anywhere that the moisture condensates will be a potential habitat for mold growth. This is why you typically find it growing on or near windows, air vents, ceilings, and on walls.

What does mold need to grow?

As mold and mildew are types of fungus, and can be surprisingly complex organisms. Their requirements however are fairly simple. All mold needs to survive is a source of moisture, nutrients to feed off, and a lack of airflow.

The moisture is provided by either high humidity environments and the subsequent pooling or condensing of water, or from water damage/spills. A humidity level of 55% is all that is required, and in humid climates, this level is easily reached through several months of the year, making mold a real problem.

Nutrients most often come from dust particles and a general lack of cleaning that can lead to an accumulation of organic materials which are then used for sustenance. And finally, a lack of airflow can come from simply not opening doors or windows to allow fresh air to circulate the room and remove moisture.

How does a dehumidifier stop mold growing?

A dehumidifier can help protect you against mold by removing one of the key elements it needs to grow, moisture.

Without the correct level of humidity, moisture will not be able to condensate and provide mold with the moisture it needs, so it will dry out and enter a state of hibernation until its circumstances become more favorable.

Dehumidifiers have the option to set the percentage of humidity within a room, so as long as you set this percentage to 50% or lower, you are making the room far too dry for mold or mildew to be able to successfully grow and reproduce.

Does a dehumidifier kill mold?

It must be made perfectly clear here that dehumidifiers are not designed to kill mold, however, what they can do is prevent mold from growing in the first place by keeping the moisture level too low, and it can also dry out mold that is already present within a property.

When the humidity level of a room with mold already growing in it becomes too, it will not die as such, but it will dry out and become dormant. If the moisture level of the room were to increase, the mold will begin to spread once again, but drying the mold out does give you the perfect opportunity to make sure it is removed in its entirety.

Once the room has been fully cleared of mold, you can set your dehumidifier back up so that it keeps the room below 50% humidity, and prevents any more instances of mold growth.

How effective are dehumidifiers against mold?

A dehumidifier will only be effective against mold if it is used correctly. For example, if the moisture setting is left at 50% humidity, the room should dry out and prevent further growth, however, if windows and doors are accidentally left open during this time, the likelihood of the dehumidifier being able to maintain a low moisture level in the room is lessened, making it less effective.

They should also not be completely relied upon and should be used as only one part of the process of mold removal and prevention.

Ensuring the property is kept clean, there are no leaks and there is adequate air rotation are other vital elements to prevent mold growth. Dehumidifiers do not kill mold, and dehumidifiers cannot remove mold, they can only slow its growth so that it can be easily removed.

Will a dehumidifier stop mold in a bathroom?

Dehumidifiers can help when placed in a bathroom by reducing moisture after bathing and can be somewhat helpful in preventing mold.

It is very important that you make sure the unit is away from any direct sources of moisture as the motor could fail and it could become dangerous if water gets into the working parts.

The unit would of course help to reduce moisture, although there are far better and more efficient methods to clear humidity after bathing, such as:

  • Installing a bathroom extract fan
  • Ensuring there are air vents to allow moisture to leave the room
  • Opening windows

The other aspect to consider when considering using a dehumidifier in a bathroom is its cost. After bathing, the moisture level in a bathroom will be extremely high, meaning the unit would have to work for a considerable amount of time to clear the room. Opening a window (if possible), is a much cheaper, faster, and safer method.

Which type of dehumidifier should you get to tackle mold?

In terms of which “type” of dehumidifier you should purchase to tackle excessive moisture and mold growth, really depends on your preferences and circumstances.

Compressor dehumidifiers can be cheaper to run (up to 50%), so if running costs are a concern or you live in a high-humidity climate, this could be one avenue to take. Whereas Desiccant humidifiers are usually much quieter, so if you don’t want to be disturbed by the unit running for long periods of time, this may also be a consideration.

Below is a selection of each that come with great reviews for you to consider.

Waykar 2000 Sq. Ft Dehumidifier for Home and BasementsOpens in a new tab. Compressor (US)

AIRGJOB 70-Pint Energy Star Dehumidifier for BasementOpens in a new tab. Desiccant (US)

Pro Breeze 12L/Day DehumidifierOpens in a new tab. Compressor (UK)

EcoAir DD1 Simple Blue MK3 Desiccant DehumidifierOpens in a new tab. Desiccant (UK)

How to tell if your dehumidifier is preventing mold

Beyond the obvious answer of “there is no mold growing”, there are several ways that you can test to see if your dehumidifier is working correctly for mold control, which are:

Checking for wall sweat

Remember that earlier I said cooler walls in a property will be where moisture will often condensate? Well, one method to check if the moisture levels have dropped is to simply pass your hand over the walls of the room. You are checking for any moisture or wet patches on the surface, if you find none, you know the moisture levels are decreasing.

Use a hygrometer

A hygrometer is a small digital clock-style device that constantly measures the humidity levels within a room. Placing one of these small devices in the room you are trying to prevent mold in is a very simple way of seeing the humidity percentage of the room. As long as you see the level is dropping and staying below 50%, you know that you are preventing mold. Hygrometers are a cheap and simple way to quickly determine the humidity level of a room.

You can also place a hygrometer in other rooms f the property to see if there is any likelihood of mold developing elsewhere. Remember, it is easier to prevent the problem than needing to treat it at a later date. There are plenty of options for hygrometers, below is a link to one that comes with some excellent reviews.

DOQAUS Digital HygrometerOpens in a new tab. (US)

NOKLEAD HygrometerOpens in a new tab. (UK)

Check the dehumidifier display screen

The small screen on the top of the unit will tell you what the current humidity level is and what percentage you have set the room to. If you can see that after several hours of running the unit is still no closer to getting to the desired humidity levels, you can see that there may be other factors in place that are raising the moisture levels faster than the unit can remove it.

Can a dehumidifier spread mold spores?

Dehumidifiers that have been used and not cleaned for a considerable time can indeed spread mold spores, as any mold growing within the unit can release spores into the air if it feels threatened.

Due to the fan within the unit, these spores can easily be expelled out of the back with the warm air, spreading the mold spores throughout the property and potentially spreading the problem from one room to multiple.

Dehumidifiers vs Air purifiers for mold prevention, which is best?

The very interesting answer to this question is that they are both highly useful for dealing with mold but in completely different ways.

A dehumidifier as we have discussed will remove moisture from a room, which will prevent mold from growing initially, and will dry mold to the point that it will become dormant and can be cleaned and removed.

An air purifier, however, will not remove moisture or, indeed, kill mold, but can trap air born allergens and mold spores from the air. So, if you already have mold within your property, an air purifier will help to reduce the spreading of spores, making the task of removing mold far easier.

So, the answer is to use both units in tandem to achieve the greatest results. Keeping the room clear of moisture whilst removing any air born spores will give you the greatest chance of successfully removing the mold without it spreading.

What else can you do to help prevent mold growth?

As well as ensuring the room you wish to prevent mold in is kept as dry as possible, there are a few other measures you can take to prevent mold growth.

Keep the room clean

Mold also requires nutrients like any other living organism, and it gets this predominantly from dust particles. Dust is made up of organic materials, one large component being shed human skin cells. These cells provide the minerals, oils, and proteins that mold needs to sustain itself.

Making sure the room is kept clean on a regular basis by vacuuming and dusting will remove the dust that mold needs, thereby removing one of its key requirements.

Keep the room ventilated

Ventilation (or lack of), is a big factor when it comes to mold prevention.

When a room is lacking in fresh air, moisture within the air is allowed to accumulate in one place where it can condense and create pools of water that mold can use for hydration.

Simple tips like opening windows and doors, inserting air vents, and adding extractor fans will all help to increase the volume of fresh air brought into a property.

New build homes are especially prone to airflow issues, as they are built to be as well insulated and airtight as possible to reduce heat loss. Whilst this is a good thing for the environment and helps to keep living costs down, it does also increase the chance of mold growth, as the air can become stale and moisture has no way to escape the building, making condensation more likely.


Dehumidifiers can certainly be very helpful in preventing mold from occurring. They will not kill mold, but they can dry a room to the point that mold will dry out and become dormant. The humidity level should be set to 50% or lower to achieve the best results, and using a combination of both dehumidifiers and air purifiers can make to process of mold removal more effective.

Chris Walker

Chris Walker has struggled for several years with mold after buying his own property. After finding the solutions to several issues around his home, he decided to create this site in order to answer as many questions about mold and mildew as possible to help others dealing with the same problems.

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