Fighting COVID19 with humidification

Building humidification is critical for people’s health !

Maintaining relative humidity in offices, workplaces, schools or any other building reduces the potential risk of transmitting viral diseases.

Many scientific studies have confirmed that  an indoor relative humidity between 40%-60% will help fighting against viruses spread on 2 fronts:

  • Air with 40% to 60% RH will limit the spread and survival of any virus such as novel coronavirus SARS-CoV2.
  • a humidified air above 40% RH will help protect mucosal barriers of human beings , resulting in an increase resistance against any microbial attack.

Here are three of what we think as the most pertinent scientific studies related to the subject:

“Maintaining a relative humidity between 40%-60% within the building environement may help to limit the spread and survival of SARS-CoV-2 within the built environment, while minimizing the risk of mold growth, and maintaining hydrated and intact mucosal barriers of human occupants.”
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Abstract from “2019 Novel Coronavirus (COVID-19) Outbreak: A Review of the Current Literature and Built Environment (BE) Considerations to Reduce Transmission” by Leslie Dietz, Patrick F. Horve, David Coil, Mark Fretz, Kevin Van Den Wymelenberg, (2019)

“There are data to suggest that outdoor absolute humidity levels affect humidity levels inside and that simple humidifiers may be adequate to raise absolute humidity to levels associated with a significant reduction in influenza virus survival.”
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Abstract from “Influenza and humidity: Why a bit more damp may be good for you!” by Jane A. Metz, Adam Finn, (Journal of Infection (2015) 71, S54-S58)

“The relationship between inactivation and RH was not monotonic, and there was greater survival or a greater protective effect at low RH (20%) and high RH (80%) than at moderate RH (50%).”
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Abstract from “Effects of Air Temperature and Relative Humidity on Coronavirus Survival on Surfaces” by Lisa M. Casanova, Soyoung Jeon, William A. Rutala, David J. Weber, and Mark D. Sobsey, (2010)


SARS-CoV-2 is transmitted by aerosols


CDC (Centers for Disease Control and Prevention) and the WHO (World Health Organization) recognize that “pathogens that are primarily transmitted by close contact (i.e. contact and droplets) can sometimes also be transmitted by air in special circumstances”.

‘’The virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak, sing or breathe heavily. These liquid particles are different sizes, ranging from larger ‘respiratory droplets’ to smaller ‘aerosols’. ‘’

Inadequate ventilation or air treatment allows an accumulation of small respiratory droplets and airborne particles that can remain viable and infectious in aerosols for hours.

The smaller the virus particle is, the longer the spread will be and the humidified air will act directly to stop the spread. This is explained in a study by Makoto Tsubokura, team leader for computational fluid dynamics at Kobe University and the RIKEN Institute. When the droplets come out of your mouth, they mix with the air and disperse. But when the air is dry, the droplets evaporate faster. As they evaporate, what we call aerosolization progresses. So, the droplets that would have fallen on the floor disperse more if the air is dry.

Maintaining air humidity between 40% and 60% indoors would allow a better fight against coronaviruses by reducing aerosol contamination.

How humidified air is helping us?

Above 30% relative humidity, human body’s defenses are stronger.
Air that is too dry can be harmful to health due to dehydration.


Humidity is an essential condition for well-being : 
Humidified air protects the human body and prevents dryness of the skin, eyes and lungs:


  • The skin is our first body barrier that needs to be hydrated to prevent itching, cracking and bleeding.
  • Tears protect our eyes from outside contaminants.
  • A dry nose, dry throat or dry lungs can increase the risk of respiratory infections.


Human body contains at least 65% water, humidified air is essential to maintain hydration, increase our immune defense and prevent health issues.

ASHRAE Epidemic Task Force



Dry air below 40% RH has been shown to:

    • Reduce healthy immune system function (respiratory epithelium, skin, etc.)
    • Increase transmission of some airborne viruses and droplets (COVID-19 still being studied)
    • Increase survival rate of pathogens
    • Decrease effectiveness of hand hygiene and surface cleaning because of surface recontamination or too-quick drying of disinfectants

Thanks to recent studies by ASHRAE, an international technical organization in the field of HVAC engineering, we have more information and new directions for HVAC systems to help mitigate SARS-CoV-2 transmission. 

More information


Isothermal or adiabatic humidification?

Air humidification is one of the essential Indoor Air Quality element to control in order to fight against SARS-CoV2 causing COVID19.  are the humidification methods equal?
Is adiabatic humidification equal to isothermal humidification? Humidity is an essential condition for well-being : 

Isothermal humidification produces hot steam from boiling water. Energy to evaporate the water is introduced by a water heating source once the water has turned to hot steam it will be naturally a quickly absorbed by surrounding dry air with no more energy exchange.

With isothermal humidification, steam at 212F [100C] injected into the air will kill any pathogenic particles (bacteria or viruses) present.

It is pure, sterile and there is no additional risk of contamination from water; since, if any it would have been killed by heat-up water to the boiling point.

IER steam humidifier
IER steam humidifier

Adiabatic humidification is adding water to the air by using energy from surrounding air, fine droplet of water will evaporate to the air or  air will pass through wetted media. Since water evaporation is done by transfert of energy from surrounding air, the air is cooled as well as humidified.

Adiabatic humidification uses a source of cold water, which need to be free from contaminant before evaporation to the air. There are many strategies to reduce pathogenic particles from water itself, like filtration or purification such as Reverse osmosis filtration or deionization process, or with UV disinfection. 

Unfortunately, decontaminated or disinfected water evaporated into the air will not be able to eliminate pathogenic particles from the air, it will only pick them up and transport them further.

ACA atomizing humidifier
ACA atomizing humidifier

In conclusion, isothermal humidification using steam humidifiers is a better solution to fight against SARS-CoV2 causing COVID19 disease since the hot steam injected in the air is pure and sterile (free for any germ). This steam will kill any virus particles that would be in direct contact with the steam.          


                                                                                                                                                                Contact us, if you need help


Electrode boiler and resistive type electric steam humidifiers compared


In this article I will explain the difference between electrode boiler and resistive type humidifiers.
They are both producing steam and use electricity as source of energy but they are based on two completely different principles of operation.
Knowing their differences and their limitations will help you to select the best technology for your application.

How electrode boiler humidifiers generate steam?

Electrode boiler humidifier uses electricity flowing through streams of water to create steam. The conductive properties of water are used to carry electric current. The current drawn and therefore steam production relies on water conductivity (typically between 125 and 1250 µS/cm) and also on the water level covering the electrodes surface.





How resistive type humidifier is making steam?

A resistive type (or resistance type) humidifier uses immersed electric heater to heat up the water to the boiling point to produce steam. Current drawn by the humidifier is the result of Ohm’s law; it is constant and only relying on the resistance value of the heater.

Steam output and accuracy

Steam output of electrode boiler humidifier is a direct function of water conductivity and water level. The cleaner and purer the water is, the lower is its conductivity. Water conductivity contained in electrode boiler humidifier cylinder will increase as the humidifier is producing steam. Steam is free of minerals, salts or other substances, so all of those substances stay in the remaining water until a blow down is performed to renew water contents.

Another factor affecting steam output is the amount of scale or lime stone accumulated on the electrodes. Scale is the result of the precipitation of the minerals and salts contained in water. This process is absolutely inevitable for any electrode boiler humidifier as the use of tap water (city water) is required by its principle of operation.


Humidity output accuracy cannot be better than +/-5% RH for electrode boilers, furthermore the steam output will slowly decrease over the operation of the humidifier until the steam output cannot supply the demand. Then the cylinder has to be replaced.

For a resistive type humidifier, steam output is independent from water conductivity (or other conditions), also the possible scale build-up on the heating element will not affect the steam output of the humidifier. Humidity output accuracy for resistive type can be as low as +/-1% RH. This accuracy is maintained over the life of the humidifier.

Water quality

As already mentioned, an electrode boiler needs water conductivity (impurity) to be able to operate, so this type of humidifier cannot accept treated water such as RO or DI water.

Reverse osmosis (RO) is a water purification technology that uses a semi permeable membrane to remove ions, molecules and larger particles from drinking water.
Deionized water (DI), often synonymous with demineralized water, is water that has almost all of its mineral ions removed. Deionization is a chemical process that uses specially manufactured ion-exchange resins.

Resistive type humidifiers can accept very pure water such as RO or DI water. However most manufacturers offering this type of humidifier will use poor materials and/or have limitations due to their water level sensing devices, so they will impose an added cost option for their humidifier able to operate with RO or DI water.

IER humidifier by steamOvap can accept any type of water from tap (city water) to RO water without additional option.


Electrode boiler service consists in removing the ”consumable” plastic cylinder that is not able to produce enough steam anymore by a brand new one.

No recycling program is yet offered by manufacturers for this plastic and electrical spare part that will end in the waste.


In the contrary  steam cylinder of a resistive type humidifier is a pemanent part usually made of stainless steel. When tap water is used, this one needs to be serviced. The service consists in opening the cylinder and removing the accumulated scale inside.

This operation can be labour and time consuming and complicated thus requiring special skills and tools for most of the resistive type humidifiers on the market.

This is not the case with IER humidifier by steamOvap, thanks to its patent pending ‘‘guide & lock’’ system that allows you to open and clean the steam cylinder in a few minutes without needs of tools or special skills.

Cost of ownership

Initial cost to purchase an electrode boiler humidifier is lower than resistive type humidifier.

Most of the humidifier manufacturers are offering both technologies. They price electrode boiler humidifier much lower than their resistive type ones. Their pricing is done the same way printers manufacturers do with ink jet printers versus laser printers. Just like ink jet printers, electrode type humidifiers are cheaper to purchase, but as they will be used and operated the consumables will represent considerable costs:ink cartridges for printers or spare plastic cylinder for electrode boiler humidifiers.

Its low initial costs makes electrode boiler humidifier the contractors choice. Most of the time required future spares are not included in the initial budget. This is a very lucrative business for humidifier manufacturers and one of the reasons electrode boiler humidifier is their entry level product.

IER humidifier price is very competitive; furthermore no spare is required for the service of the humidifier. It is the only humidifier on the market offered with a 3 year warranty.

In any case, total cost of ownership is in favor of resistive type humidifier, after only 18 months in average.


When selecting electric steam humidifier, electrode boiler can be very attractive as promoted by other humidifier manufacturers. Reason is simple: they want your business of spares plastic cylinders for the years to come.

Unless you are not concerned by inaccurate and unstable steam output, plus the cost of spare cylinder replacement over the life of the humidifier and the resulting waste of plastic in the field, then electrode boiler humidifier should be your option.

If you prefer to ensure a good humidity control, save energy by using pure water, as well as lower your environmental impact while optimizing the total costs of ownership for the building owner; then resistive type is the best choice for electric steam humidifier.