Do Air Purifiers Help With Mold?-Yes but 4 other things are “crucial”

It is unpleasant to live with mold which can be difficult to get rid of. So an instant fix with an air purifier is very attractive.

As a general rule an air purifier with a HEPA filter will easily remove mold spores. The air purifier needs to have a high enough air flow, at a noise that you can tolerate, to clean the volume of the room at least 5 times every hour to reduce the spore count in the air 80% or more. Also a carbon filter in the air purifier will deal with any fungal odors.

So lets investigate further-

[Mold grows in damp places, the water in moisture is enough for it to grow. It spreads by producing microscopic spores that can germinate if they land in a moist environment. Spores are everywhere in our outdoor air and inevitably enter our homes. They are not the only problem, fragments of the indoor mold itself can enter the air and act as an allergen to produce an allergic reaction.

Indoor mold may not be obvious, it can be hidden behind a dry wall, under wall paper or above ceiling tiles, just because there is no visible mold does not necessarily mean that you do not have a mold problem.

Hepa Filtration is Needed

HEPA filtration in a standard HEPA air purifier will essentially remove all of the airborne mold spores and mold particles from the air going through the filter. HEPA filters find particles 0.2 – 0.3 micrometres in diameter the most difficult to remove. So as mold spores are 2-20 um in diameter a true HEPA filter will easily remove them. The main way that they do this is by the basic sieve mechanism whereby large particles cannot get through the gaps in the filter, like peas in a collindar. Please see diagram below-

do air purifiers help with mold
Filtration efficiency and the mechanisms underlying it for a HEPA filter

So a true HEPA filter will have no problems dealing with mold spores.

The more carbon the filter has the more odor it will remove and the longer it will keep working. The filter below is exceptional in containing 5lb of activated carbon granules. A replacement filter will only be needed after 24 months, is from the iQair HealthPro Plus which I have written an article about here.

Diagram showing the percentage filtration at various particle sizes. At the size of fungal spores, and other airborne allergens, such as house dust mite, and pet dander a HEPA filter is virtually 100% efficienty in removing them.

Beware of air purifiers that state the filter is “HEPA like”, “99% HEPA or state how good the filter is over several paragraphs without stating that it is a HEPA filter. An air cleaner with these specifications will probably not have a HEPA filter or the manufacturer would have said so.

HEPA filtration is central to modern air cleaners and is the core technology that allows us to improve our indoor air quality. Other technologies have been developed but tend to perform much less well than HEPA filtration in removing particulate air pollutants.

So air purifiers help with mold by essentially removing all mold particles from the air.

Adequate air Flow-5 Air Changes per Hour

However even a brilliant filter will not help if the amount of air processed by the air purifier is not high enough. One air change per hour for a room is when the a volume of air the size of the room goes through the air purifier once in an hour.

The EPA recomend that when using an air purifier there should be a minimum of 5 air changes per hour. This will lower particle count 80%, so 20% of airborne particles are still left in the air. A higher number of air changes per hour will lower the particle count further but if you put your air purifier on a lower setting eg sleep mode because of the noise you may only reduce the particle count by 30%.

Diagram to illustrate the importance of air flow in filtering room air

So the most important part of choosing the air purifier is asking yourself the question “does it have enough airflow for my room at a noise level that I can tolerate”. So never buy an air purifier for its maximum air flow as you will find this fan speed too noisy. In fact the next fan speed down in some air purifiers may be too noisy. What is too noisy for longterm use will vary from person to person. For me anything above 50db is too noisy.

Another rule is not to let the air quality indicator decide the fan speed as the sensors that the air purifiers use are too inaccurate. I have written an article about this here.

Sealing the Area With Mold Off

There are 2 reasons for wanting to seal the area with mold off-

  • So appliances such as air purifiers and dehumidifiers are working on a limited amount of air and can be fully effective
  • So that mold does not spread to other areas of the home

Carbon filter in Air Purifier Will Help Get Rid of Mold Odor

One of the air quality problems with mold is its odor it is a “musty” smell. Here an air purifier can help as well. These smells are caused by volatile organic compounds which a different kind of filter in the air purifier can remove-an activated carbon filter. Activated carbon has a great abundance of microscopic fissures into which molecules of volatile organic compounds can enter. Once the volatile organic compounds into deep into the activated carbon the activated carbon molecules attract them and keep them lodged deep in the carbon. In this way an activated carbon filter removes the molecules that are causing odors from the air.

The activated carbon filter of the iQair HealthPro Plus-5.5lb of activated carbon. The granules of carbon can be seen in the right hand panel
The activated carbon filter of the iQair HealthPro Plus-5.5lb of activated carbon. The granules of carbon can be seen in the right hand panel

So in addition air purifiers help with mold by reducing odors but can they be even more effective-

Can air purifiers kill mold?

A standard air purifier with a HEPA filter simply traps the mold spores and particles but does not kill them. In many ways there is no need to kill them as they are harmless trapped in the filter. Therer are other technologies which can kill them-

UV Light in an Air Purifier

As a general rule mold spores cannot be inactivated by the UV light in a home air purifier.

This may seem strange as some air purifiers have UV lights to try to kill microorganisms. UV lights damage DNA and so stop microorganisms growing and dividing effectively “killing” them. UV light works best when DNA is most vulnerable. This is when it is being used and is in a relatively open configuration. Mold spores are inert, their DNA is not active and vulnerable. So they are resistant to UV light and take a very long time in UV light to be inactivated. In an air purifier mold spores in the air stream are whisked by the UV light and only irradiated for a fraction of a second.

This is simply not enough time for the UV light to be effective. Further discussion of this point can be found in this article.

PECO Photoelectrochemical Oxidation

PECO is used by the Molekule and can destroy spores but only the spores that come within the vicinity of the device will be inactivated. It is encouraging that this approach has been found to be effective for viruses. However for particles this approach has was tested by the NY Times Wirecutter who reported that it was not very effective for particles.

An Air Purifier is Better For Mold in a Localised Area Than an HVAC System but an HVAC Air Purifier is Better at Improving Air Quality in the Whole Home

An HVAC system with the right filter can potentially improve the background quality of air in your home, I have written an article about this here.

Although an HVAC system will improve the air significantly it will not be as good as an air purifier in a particular room processing the air 5 or more times per hour.

4 Crucial Things That Need to be Done Next if You Have Mold

Isolate the Area if Possible Until the Mold is Dealt With

This is to stop a high concentration of mold spores and allergens spreading throughout your house. This may help prevent allergic reactions and make it less likely that mold will grow elsewhere.

Stop the Mold Growing

Even with good air purification there will still be 5-20% of the mold products in the air and so there is a need to stop the mold growing and also to remove it.

The best way to stop mold growing is to deprive it of water. This can be done by reducing the relative humidity below 80%. The quickest way to do this is to use a dehumidifier. So you may wish to buy one to keep the humidity in the area with mold at 30-50%, this should stop the growth of mold.

Remove the Defect That Allowed it to Grow In The First Place

The source of the moisture also needs addressing. If it is a leaky roof or breach of basement water proofing the source of the leak needs fixing. It may be that the area you are in has high levels of humitidy at some times of the year and then a whole house dehumidifier may be the best option.

Mold prevention is also important, as a general rule to prevent mold growth any water damage to your home should be dried out within 24-48 hours. This is likely to prevent mold from starting to grow

Remove the Mold

Once you have removed the conditions for mold to grow you should consider how to remove any mold. The EPA recomends that if the patch of mold is 3 feet by 3 feet or less then you could do it yourself but if it is larger it is best to get a professional contractor in to do it. I would add that if you have any respiratory condition or problem with your immune system that you should not do it yourself.

If you do remove the mold yourself you should have a mask to prevent you breathing high levels of fungal fragments and spores into your lungs. I have written and article about the best type of mask to get here.

There is a very useful EPA guide as to what to do if you find household mold here.

Health Problems From Mold

Allergic Reactions

The majority of health problems for mold are with allergic reactions to the mold allergens. This can lead to a runny nose, sneezing, rash, and red eyes-general allergy symptoms. It can also lead to asthma attacks in people with asthma.

Inhalation of mold fragments/allergens can cause a hypersensitivity pneumonitis ie inflammation of lung tissue or organic dust toxic syndrome.

Can mold grow in your lungs?

Mold can grow in damaged lungs or in people with a problem with their immune system. It is rare for it to grow in healthy lungs in people with an intact immune system. Aspergillosis is an example of this.

These are some of the more common manifestations of exposure to mold but there are others. If you think that you may be affected by mold you should consult a health professional.

Mildew is another type of fungus that grows when there is water available. As a general rule Mildew tends not to damage the surfaces on which it is growing like mold does. Also it is easier to remove and has fewer health implications.

Conclusion-do air purifiers help with mold?

Air purifiers help with mold and will remove a high percentatge of from the air. A HEPA filter is the basic standard that the air purifier should have. Then the degree of removal mainly depends on the air flow that you have the air purifier on. This should be a minimum of 5 air changes per hour.  

You will also need to stop the mold growing. The quickest most effective way of doing this is to use a dehumidifier to deprive it of water that it can get from moisture in the air.

Then you should mend any leaks that have let water in.

The existing mold hopefully now not growing should be removed but whoever does this should wear a very high efficiency mask. This is to prevent high concentrations of spores being breathed in.


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Whole House Dehumidifier-9 Important Factors-an article about the types of whole home humidifier and the advantages and disadvantages which can be found here.