Buying an Air Purifier for Mold

mold air purifier

A mold is a fungus. And like other fungi, mold loves to feed on organic matter. In nature (outdoors) this is a good thing. Mold plays a crucial role in the decomposition of organic matter – and, as we all know, decomposition of organic matter plays a crucial role in a healthy ecosystem.

Inside your house, well, let’s just say mold isn’t as desirable. The mold itself and especially the microscopic spores it releases into the air (to reproduce) can lead to a variety of different health problems.

So, what can you do about it?

First, it’s important to understand how mold proliferates in the home. This can be broken down into four steps:

  • the mold spore lands on a surface
  • the mold spore only grows and eventually reproduces if it has access to food – let’s say it does – let’s say it lands on a piece of food like a piece of bread
  • with access to food, the mold starts growing – it grows by extending filament like structures called hyphae
  • some of these hyphae produce more spores which are released into the air and the cycle continues

This gives you TWO things to combat

  • mold – the network of hyphae (called a mycelium)
  • mold spores – airborne mold ready to land on a surface and start growing

Combat mold itself

To combat mold itself you need to make it difficult for it to grow. Mold needs

  • moisture
  • proper temperature
  • food

So the first thing to do is reduce humidity in your home. You can do this by running the air conditioning and/or by running a dehumidifier. Both will lower humidity.

Temperature – unfortunately, there’s nothing you can really do here as molds love room temperature. Few molds can grow at temperatures at or below 4 °C (39 °F) and this is why most fridges are set to this temperature. Unfortunately, setting the temperature in the home this low isn’t an option for most people.

Reduce food – this one is more difficult than you may think. Obviously you want to keep food sealed and keep some food stored at cold or freezing temperatures. But note that mold’s food options aren’t limited to human food. Yes, mold absolutely loves to eat human food but it finds other organic matter just as appetizing. The truth is that mold can feed on anything as long as its organic matter – it doesn’t matter if it’s human food or not.

A good example of other types of organic matter? Dust. Dust is comprised of a myriad of different types of particles including organic particles.

Of course, you can absolutely keep all surfaces in your home clean of dust to prevent mold growth. But you can also reduce airborne dust with an air purifier.

This is the first way an air purifier can help to reduce mold growth in your home. It can help to combat mold itself by reducing a component necessary for mold to live – by reducing the concentration of organic particles in the air.

Next, we’ll look at the second way an air purifier can reduce mold growth in your home – by removing mold spores – the means by which mold reproduces – from the air.

Combat mold spores

Two things make mold spores difficult to deal with:

  • Their inherent characteristics
  • The fact that they’re found in large numbers


Mold reproduces by mold spores – so spores are made in such a way to make reproduction as effective as possible.

Spores can be

  • Hydrophobic and adapted for wind dispersal – especially bad because this means that mold spores can easily become airborne (disturbed) even after settling
  • Resistant to UV radiation
  • Sheathed for water dispersal
  • Sticky – able to cling to fur and clothing for dispersal
  • Able to withstand extreme temperatures and pressures - unlike the mold itself, spores do not need humid conditions to survive – they can survive just fine in dry conditions

Large numbers - outdoors

Here’ the thing: mold is everywhere and therefore mold spores are everywhere. Why? We mentioned it at the beginning of this article: mold is a necessary part of decomposing organic matter outdoors in nature.

Right now, wherever you are, there are mold spores floating around in the air around you. Every time you go outside the concentration of mold spores in the air increases. The concentration outdoors can be as low as 50 spores per cubic meter of air all the way up to thousands of spores per cubic meter of air.

This is why, if you’re sensitive to mold allergies, the CDC advises that you stay away from compost piles, cut grass, and wooded areas – these are all areas ripe for decomposition – and mold.

Large numbers - indoors

Every time you open a window, every time you open a door, air filled with mold spores floods your home. Mold spores land on organic matter where they immediately start feeding and growing. Nonetheless, it’s only when conditions are especially hospitable (high humidity, etc.) that they grow and reproduce to a point where it becomes an actual issue. In other words, some mold spores, albeit at a low concentration is perfectly normal inside your home.

Most mold remediation companies use guidelines similar to the following when assessing mold count in a particular sample of indoor air:

Under 200 spores per cubic meter of aironly especially toxic species considered a problem at this level
Over 1500 spores per cubic meter of airthreshold at which you might have a problem with common species
Over 3000 spores per cubic meter of airthreshold at which you likely have a problem with common species

High spore count always equates to an elevated presence of mold.

Sometimes this “elevated presence” is so high that it requires complete mold remediation – i.e. not just removing spores but killing/removing the mold.

Sometimes this “elevated presence” of mold is outdoors. Note that if outdoor levels are high, indoor levels will also be high so there’s not always a mold problem inside the home if mold counts are high.

Either way, the bottom line for our purposes here is that

  • mold spores can be found at extremely high levels outdoors
  • they easily enter the home
  • occur in great number indoors even at what is consider “normal” levels – ie there’s no real mold problem – and at these levels they can still trigger allergies for certain individuals

So what can you do about it?

The good news is this:

Most mold spores are in the 2 to 40 micron range (in terms of size). This makes molds spores large enough to really be filtered by any type of particle filter at all. For most other particles, we recommend a HEPA filter but mold spores are so large that you don’t necessarily have to limit your air purifier search to units equipped with a HEPA filter at all. Even no-name proprietary particle filters should be able to filter mold spores from the air just as well.

Still, we do prefer HEPA equipped units because HEPA filters are going to be able to filter a lot more than just mold spores from the air. Remember, mold feeds off of dust and dust particles can be much smaller than 2 microns. HEPA does extremely well with these smaller particles while proprietary particle filters give mixed results.

We specifically recommend HEPA equipped units with at least 250 CFM. That is, units that are able to process at least 250 cubic feet or air per minute. Such units can be had at very reasonable prices and provide far better air processing than cheaper lower CFM units.

Air processing is important because the more air the unit is able to process every minute,

  • the faster the particle concentration in the room is going to be lowered when the air purifier is turned on initially
  • the quicker the unit will be able to process new unwanted particles that enter the room air
  • the lower the overall particle concentration that is able to be achieved and maintained in the room

250 CFM units also tend to be more energy efficient and quieter at the same output when compared to smaller (lower CFM) units.

One of the best 250 CFM units we’ve tested so far is the Winix 5500-2. It’s equipped with both a washable pre-filter and a HEPA filter. Both of these filters are going to work in tandem to remove mold spores and the airborne organic matter that mold feeds off of – namely dust - from the room.

Larger particles will collect on the pre-filter. The great thing here is that it’s washable so you can clean it off and reuse it without paying for a replacement filter.

Smaller particles will make their way all the way to the HEPA filter. The “HE” in “HEPA” stands for “high efficiency” and this isn’t an overstatement of facts by any means. Once smaller particles get to the HEPA filter they’ll be stopped at a rate of 99.97%. That means that for every 10,000 small particles that get through to the HEPA filter only 3 will make it through to reenter the air. Those same 3 particles will eventually be filtered out as the air is reprocessed over and over again by the air purifier.

Again, the Winix 5500-2 is equipped with both a washable pre-filter and a HEPA filter. It is currently the single model we would recommend as the best air purifier for mold.

Mycotoxins – the third thing to combat

So far, we’ve only discussed mold and mold spores.

Mold spores in large quantities – cause allergic reactions and respiratory problems

Mold on food – can make you sick when consumed

But there’s one more mold byproduct that that we haven’t discussed – one that is also very much a health concern for humans – mycotoxins. These chemicals, produced by only certain types of mold, become airborne in multiple ways:

They can be found in

  • Spores
  • Mycelium debris
  • Small particles of dust (the toxin is excreted by the mold and absorbed by the particle of dust)

For the purposes of this discussion we’ll call all three of these “carriers” of mycotoxins particles. Studies show that mycotoxins are found in particles ranging from 0.65 to >7 microns with most being found in particles in the 3.3 to 4.7 micron range.

Here again, a HEPA equipped air purifier is recommended. And again, a 250 CFM unit is recommended.

So while we’ve added yet a third type of particle to the air that you need to worry about if you have mold problems in your home, there’s still only one type of air purifier we recommend for the job: a HEPA equipped 250 CFM unit.

Such a unit will be able to effectively remove

  • airborne dust that mold feeds off of
  • airborne mold spores
  • airborne mycotoxins “carriers”

Again, the specific model we would recommend here as the best air purifier for mold (including dust, spores, and mycotoxins) is the Winix 5500-2.

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Comments (2)

Consumer Analysissays...

Most of the particles of concern are trapped in the HEPA filter which is replaced - not cleaned. The pre-filter, which is cleaned, only traps larger particles. And it should be cleaned with a vacuum which shouldn't release those particles back into the air.


Thank you! Excellent analysis. Question: Is it dangerous to clean the filters?

It's great that the mold spores, dust, and mycotoxin/carriers are trapped, but what happens when you open the unit. Aren't you in danger of inhaling a BIG dose of them?

If not upon opening the unit, then perhaps when you wash the filter -- doesn't that stir it up and set some of the particles free?

How is this handled?