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Humidifier 03 1200px Depositphotos 402137558 xl 2015

Using an Air Purifier and Humidifier Together-Hidden but Rare Problems

Like me you are probably wondering how humidity affects an air purifier and whether a humidifier could actually stop an air purifier working efficiently. The two appliances can form a good combination with the humidifier providing the optimal amount of water vapour in the atmosphere for our comfort and the air purifier reducing the level of particles in the air to protect our health.

As a general rule a humidifier and air purifier can be used together. The overall humidity in the room should not exceed 90%. Otherwise, the efficiency of the air purifier HEPA filter plummets. So if you do use the 2 together, it would be wise to have a humidity meter.

As the effects of air pollution on health become more apparent, air purifiers (“air cleaners”) are being increasingly used to remove air pollutants. The most well-known particles are pet dander, mold spores, airborne allergens, and house dust mites. House dust mites multiply quickly in humid conditions. So quite apart from interfering with the air purifier you should avoid humidity levels above 50% to stop them multiplying. You should also avoid humidities above 80% or mold (fungus) may start growing in your house.

However, other airborne particles are probably a greater health problem-ultrafine particles. Although not widely appreciated, ultrafine particles in the air can enter our bloodstream. In this way they can affect organs throughout our body and even reach the fetal side of the placenta. It is also becoming apparent that the amount of harmful particles in the air needed to affect health is within the range was previously thought to be safe.

Air purifiers are also thought to be useful in reducing the transmission of viruses from person-to-person. There are also special situations such as forest fires which produce particles that are now thought to be more dangerous than smoking! Air purifiers can remove these particles from the air as well as chemicals.

Humidifiers can help if you have very dry air in your home as they produce humid air. They simply add water vapour to the air they do not remove particles or chemicals from the air.

So why can also humidifying the air be a good idea?-

Adding a Humidifier to an Air Purifier Can Have Health Benefits

If the humidity in your home is very low a humidifier can help your health in several ways-

1) A humidifier is Likely to Lower the Severity of Viral Respiratory Infections

If the humidity of the air is too low, humidifying the air can protect us against respiratory infections. One of our defence mechanisms, mucociliary clearance of our airways, relies on mucus in our airways trapping particles, bacteria and viruses and being continuously moved up and out of our lungs. If the air is too dry, the mucus becomes stickier and more difficult to move. So at very low humidities when this mechanism is impaired viral respiratory infections such as influenza can be more severe.

In one study mice at low relative humidity (10-20%), developed much more severe influenza. This found that other defence mechanisms in the lungs were also impaired-

  • Mucociliary clearance, so the virus was not cleared from the airways as well
  • Innate antiviral defence
  • Tissue repair function

2) A Humidifier May Relieve a Dry Cough

If the air is too dry, the mucus becomes stickier and more difficult to move. This can also lead to collection of mucus in parts of our airways, causing irritation and coughing. This would only apply if the dry cough is caused by low humidity. There are of course plenty of other causes for dry coughs. If you have a cough that is persistent for longer than 2 weeks, you should always see your physician.

3) A Humidifier May Prevent Mucous Membranes in Your Nose and Throat From Drying Out

If the air is too dry, it can cause our mucous membranes to dry out. Mucous membranes are surfaces in our bodies such as our mouths, nasal passages and throat which can become sore and uncomfortable if they dry out. Nose bleeds may be related to low humidity. Also, our lips can become chapped, which can be made better by raising the humidity.

4) A Humidifier Can Prevent Very Dry Skin

Some people notice dry skin in conditions of low humidity, and people with eczema or other skin conditions may find that their skin is worse under conditions of low humidity.

Another benefit of a humidifier is that it may protect wooden objects or flooring in our houses. This is because anything made of wood in our houses will shrink and warp as it dries out. This can lead to cracks around door frames and of course problems with wooden flooring.

The ideal level of humidity is 30 – 50%.The humidity in the air is higher in the summer and lower in the winter. So you may need a dehumidifier in the summer and the humidifier in the winter in addition to an air purifier.

Looking into this, I found some very interesting facts about how humidity alters that function of an air purifier and the comfortable range of humidity.

Effect of Humidity on a HEPA Air Filter

Once the humidity gets above 90% the efficiency of a true HEPA filter drastically declines.This is shown by the following diagram –

Humidifier using an air purifier and humidifier together Ver 01 1
Diagram of the change in HEPA filter efficiency with increase in humidity. Drawn from data in this reference.

However, it is reassuring that for most of the range of humidity the filter performs its function of reducing particles from the air very well. We just have to be careful to avoid very humid conditions.

Another potential problem with continual moisture on the HEPA filter is the possibility of fungi growing on the filter. The air stream through the filter would then take fungal spores and particles into the room air.

So although both an air purifier and the humidifier can be used at the same time, it would be best to place them as far apart as possible

Effect of The Air Purifier on Humidity

The air purifier working will not make any difference to the humidity in the atmosphere. There is nothing in the air purifier that will absorb a significant amount of water vapor.

A humidifier with an ionizer
A humidifier with an ionizer

Position of Air Purifier in Relation to Humidifier

They should be as far apart as possible. This is to make sure that the air purifier filter does not become saturated with water droplets. The worst combination would be for the outlet of the humidifier blowing humidified air into the intake of the air purifier.

Effect of Humidity on Air Purifier Particle Sensors

Humidifiers may also affect air purifiers by altering the reading of any inbuilt air quality sensor. The sensors that are built into air purifiers are usually relatively cheap and use infrared technology rather than more accurate laser diffraction. The infrared sensors consist of an emitter and an infrared receiver. When the receiver detects the amount of light reaching it has decreased, it assumes this is due to air pollution. The greater the decrease, the more air pollution it registers, and the higher the speed it runs the air purifier at. Water particles can absorb the infrared radiation and so appear as pollution. As the humidifier produces water particles, the air purifier thinks that the pollution in the room has increased.

Incidentally, I would never recommend running an air purifier using the internal sensor. You should always have a separate air sensor which uses laser diffraction as the technology to check the air quality in the room. This is a much better way to check that you are reducing the particle count adequately to protect your health.From my own experience, it is quite surprising how much the particle count in the air changes. Without a meter it is impossible to tell. Almost certainly many people who use air purifiers in bedrooms must be turning them down, because of noise, to levels that they do not realize are ineffective.

Young child looks at water vapour from a humidifier
Young child looks at water vapour from a humidifier

Effect of Humidifiers on the Carbon Filters of Air Purifiers

Activated carbon filters remove pollutant gases/chemicals from the air. These airborne contaminants are removed both by physical adsorption and chemisorption. In physical absorption the gas molecule travels into a pore in the carbon. It then impacts the walls and is trapped by intermolecular forces. The surface area of carbon filters is very large per gram of carbon – approximately 2000 m²/g. So each gram of carbon provides the surface area at approximately the equivalent of fall football playing fields!

An air purifier can have an activated carbon filter weighing more than 2.5kg, although most have a thin coating on a thin filter.

Chemisorption is where there is direct chemical reaction between the gas and the material in the filter. At higher levels of humidity, water molecules are adsorbed and so prevent the chemisorption of gasses. So as a general rule for a carbon filter to work well, the humidity must always be below 60%.

Effect of Humidifiers on Air Quality

Distilled water must be used with ultrasonic air purifiers, as otherwise mineral particle may be added to your home’s air. So whilst the air purifier is trying to reduce particles in the air, the humidifier may be adding them. There is a case report of the lungs of a young child being damaged by an ultrasonic humidifier. So using the wrong water in a humidifier can reduce air quality.

Another way in which humidifiers can impair the quality of the air is if bacteria and fungi grow in the water, the humidifier then disperses into the room. So it is better to use distilled, and hence sterile, water in a cool mist humidifier or an evaporative humidifier to avoid bacterial growth in the humidifier water. This is particularly so in the case of a cool mist humidifier or a vaporiser used in cold mode. Warm mist humidifiers and a vaporiser used in “warm” mode heat the water so killing bacteria and fungi. So starting with sterile distilled water for these is not so important.

The two devices can be combined in an air purifier humidifier combo. An air purifier humidifier often leads to a compromise in specifications, especially regarding the air purifier element. Often an air purifier combo will not have true HEPA filters and so is not really adequate for air purification.

Humidifier emitting jets of water vapour
Humidifier emitting jets of water vapour


Using an air purifier and humidifier together is possible to improve your indoor air quality. Also, as a humidifier and air purifier address different aspects of air quality, it will sometimes be necessary. Possibly only for parts of the year, most likely in the winter when the humidity level is lower. This is not a problem provided the inlet for the air purifier is not near the outlet from the humidifier. This is because humidity is greater than 90% decrease HEPA filter performance tremendously.

In addition, water droplets in the air will confuse the inbuilt air sensor in most air purifiers to make the air purifier think the air is more polluted than it really is. Whilst you need to be aware of this potential interaction ideally would not be using the inbuilt sensor of the air purifier anyway. It is better to have an external air quality meter. The reason is these use different technology and are more accurate.

So as a humidifier can potentially change the function of an air purifier, it would be best to situate the humidifier as far away from the air purifier is possible.

Related Questions

See Also

Different Types of Humidifiers-Only 1 Type Will be Perfect For You

Do Humidifiers Help With Asthma? Yes in 2 Important Ways

Whole House Humidifier-7 Reasons It Is So Much Better Than Several Portable Units

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