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Most Common Air Conditioner Germs

Most Common Air Conditioner Germs (+ 5 Things to Do About It)

We all know this. Switching the AC on is the best way to beat the hot and sweaty summers in Brisbane. Besides, the air filters in the unit can filter out air pollutants as well.

But what if your air conditioner hosts a colony of germs that can adversely affect indoor air quality?

In that case, you are risking air conditioning sickness resulting from inhaling a wide range of viruses, bacteria, and mould. Since an average Australian spends 90% of their time indoors, the risks are considerable.

The good news is, you can prevent this from happening by taking a few precautions. Yes, your aircon (or ANY aircon, for that matter) is a veritable germ party. But first, you can cut down on their amount. And second, the fact that there will always be some doesn’t mean you’re doomed.

So what causes the growth of bacteria in air conditioning systems?

Let’s find out.

Types of Microbes in Air Conditioning

With all the comfort that air conditioning systems offer, they can be a major source of airborne infections in any indoor environment.

Think I’m exaggerating?

There have been a few studies to identify the type of bacterial communities found in HVAC systems. In one study conducted in Japan, five major bacterial categories were found in dust samples collected from sample units. Other forms of bacteria were also found in fewer numbers. 

The common places where these bacteria were found are the filters, fans, coils, and air vents of the AC unit. The density of the bacterial categories in an AC unit depends on the environment of the location and the occupant activity.

Air Conditioner Filter Replacement

The categories of bacteria found in air conditioners in the study are:

  • Proteobacteria
  • Firmicutes
  • Actinobacteria
  • Cyanobacteria
  • Bacteroidetes

Among those identified, three of the bacterial genera have potential health risks. Beyond that, an HVAC system can also help in the transmission of viruses, especially in crowded spaces.

Environments that have a heavy density of workers and visitors will have a more dynamic density of pathogens. This can cause a wide range of respiratory ailments including allergic rhinitis, asthma, and pneumonitis.

The other microorganism commonly found in indoor air is mould or fungi. The cooling ducts in air conditioners can be breeding grounds for various types of toxic hygrophytic fungi.

One research pointed out three common types of fungi found in an air handling unit.

  • Penicillium corylophyllum 
  • Aspergillus versicolor
  • an unidentified Cladosporium species

Quite simply, it is not uncommon for microbial life to colonise air filter surfaces. In many case studies, the fungal contamination levels were higher than the safe limits set by the WHO. This can be a health risk, especially for young and immune-depressive patients.

The main reason for that is the mycotoxins that come as a result of the mould-breeding in a dirty air conditioner. Inhalation of these toxins can cause inflammatory diseases and autoimmune disorders. While not as widespread as bacterial and viral infections, fungal diseases are a global health concern.

Dirty Air Conditioner

A common type of mould found in the Australian climate is the Stachybotrys Chartarum, a form of black mould. This strain is toxigenic and can cause symptoms like cough, nasal irritation, wheezing, chest tightness and dyspnea. It has also been associated with the so-called Sick Building Syndrome.

According to Professor Sheryl Van Nunen, a spokesperson for the National Asthma Council, almost 40 per cent of the Australian population is atopic. This means they have “an inherent ability to be allergic”. And people with allergies, and asthma are more vulnerable to infections related to mould.

Bacteria in Air Conditioners and Sick Building Syndrome

The combination of these microorganisms in indoor air gives rise to bioaerosols which can harm human health. Bioaerosols are a major cause of sick building syndrome and can give rise to allergic reactions, respiratory problems, and infectious diseases.

Note that there are no standardised protocols for the data collection or interpretation of bioaerosols. That makes drawing definite conclusions and setting exposure guidelines from the studies difficult. Besides, the concentration of airborne bioaerosols depends on various factors like ambient temperature, indoor airflow, and relative humidity. This makes data interpretation more challenging.

So, can a dirty AC make you sick?

The answer is, yes.

While all that may sound worrying, there is no need to panic. Proper cleaning of the air conditioning filters and unit goes a long way in getting rid of harmful pathogens.

Besides, AC units can also help in reducing viral activity. Another research notes that an indoor temperature between 20–25 °C and relative humidity between 40–70% can help in weakening the SARS-CoV-2.

And not everything you hear about microorganisms in air conditioner units is true. For example, consider the issue of bacteria in air conditioning that cause Legionnaires’ disease.

The truth is, Legionella Pneumophila bacteria breed in water and not inside air conditioning ducts and filters. So water supply systems and air-conditioner cooling towers are the major breeding grounds for this bacteria. Unless the air conditioner uses a water-based system for refrigerant cooling, there is hardly any chance of Legionella bacteria infection.

Service Guy Cleaning and Maintaining Air Condition Unit

Does the Air Conditioner Kill Germs?

You may have heard about high-efficiency particulate air (HEPA) filters. These are highly effective in removing microbial contaminants from the air. They claim to remove 99.95% of particles from the air including dust, pet dander, and pollen. 

However, HEPA filters can’t remove airborne chemicals like VOCs and ozone. That’s why activated carbon, which can remove such impurities, is a part of advanced HEPA filter units.

As per the standards set by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), these filters come with a MERV rating. The higher the rating, the more efficient the filter. HEPA filters come with a MERV 17 or higher. 

A HEPA filter with a MERV 17 rating can remove 99.97% of air particles ranging between 0.3-1.0 micron in size. Beyond that, there are ULPA filters that come with higher MERV ratings and can capture 99.999% of all airborne impurities. 

During the peak of the Coronavirus pandemic, WHO recommended the use of MERV14/ISO ePM1 70-80% air filters or a filter of higher capacity in AC units. It also suggested that the filters should be periodically cleaned and maintained in line with the manufacturer’s recommendations.

Even so, these filters do not kill the germs and smaller microbes between 0.2 to 1 micron can pass through them.

Mechanical filters use various mechanisms to trap particles. The particles get trapped as the opening between the filter fibres or screen mesh is smaller than their diameter. In time, the fibres of the filter element get loaded with particles and airflow across the filter gets reduced. 

Cleaning Air Conditioner Filter

When left unclean, the accumulated particulate matter can get released downstream of the airflow and clog the air ducts. Studies have indicated that the area downstream of the filter can be a breeding ground for aerosolized microorganisms. 

These microorganisms thrive by using the material collected on the filter surface as a food source. They grow profusely when temperature and humidity ranges are favourable. Ultimately, microbes from these breeding grounds can get dispersed in the filtered air.

Moreover, if the filters are clogged, the air can find a path of least resistance to enter the room. It does so by bypassing the filters and carrying harmful pathogens with it. That makes periodic cleaning of filters a must to restore collection efficiency.

Bottom line? HEPA filters are not an absolute solution to reduce symptoms of air conditioning sickness. Even so, they are a good choice for allergy or asthma sufferers. Unfortunately, not all manufacturers manufacture HEPA filters as standard specifications. Such filters are often labelled as “HEPA-type,” or “HEPA-like.” Make sure to steer clear of such brands.

UV Lights for AC Systems: Do They Work?

As we said above, even though they are effective, HEPA filters in an air conditioner do not remove all microbes. For that purpose, modern AC units make use of UV lights to remove bacteria and other microorganisms in the system. These steriliser UV lights will kill mould within the reach of the light, as well as the viruses and bacteria that grow inside the AC unit. 

In reality, limited research has been done to study the germicidal effects of UV light on fungi. However, existing studies suggest that UV radiation generally is effective in reducing bacterial and fungal contamination in AC units.

You can add UV lights to an HVAC system, but you’ll probably have to call a professional. However, most HVAC contractors will not allow you to modify their system without voiding your warranty. So, make sure that you understand the terms of service before making any changes to the unit.

Some AC filters also use bactericidal substances on the filter surface that kill the bacteria. Different types of bacteriostatic agents are used for this. ASHRAE has recommended that AC manufacturers should ensure that these agents do not introduce chemical pollutants into the indoor air.

UV Lights for AC System

The moral of this story?

At the end of the day, no air filter will be able to clean up the indoor air single-handedly. It is necessary to keep the filter clean and remove all sources of airborne pollutants from the indoor space.

How to Keep Your HVAC System Germ-Free: 5 Things You Can Do

Always take the help of a well-trained technician to maintain your AC and keep it free from microbes. Here are the steps you can take.

  1. Routinely clean or replace the AC filters of your home and car to prevent them from clogging up. Filters of air conditioners that are heavily used in dusty conditions may need frequent replacement. Besides, cleaning will also reduce the air conditioner’s energy consumption.
  2. The evaporator coil and condenser coils of the AC unit can accumulate dirt and become a breeding ground for fungi. Keep the coils clean and ensure proper airflow around them.
  3. Make sure that the drain channels of the unit do not get clogged. Accumulation of moisture can result in a higher concentration of microorganisms. In case there is any water damage from the AC unit, fix it without delay.
  4. Do not depend solely on the AC as a source of air in the room. Open the windows to let in fresh air and use ventilation fans to circulate the air. This will dilute the concentration of bioaerosols that may be present.
  5. Those who suffer from allergic conditions and asthma can think of investing in an additional air purifier. In-duct air purifiers can help in the elimination of microorganisms within the AC and clean the air.


Air Conditioner Controller

To sum up, bacterial and other microbial infections from air conditioning units are a possibility. The health effects can be more pronounced for individuals with chronic respiratory illness and the very young.

However, there are ways to prevent that from happening. As long as the AC unit is cleaned regularly and properly there is no cause for serious concern. Make sure to schedule regular maintenance for the unit from a skilled technician.

Beyond that, clear any signs of mould or mildew from inside your home. In case you are frequently experiencing nose and throat issues, breathing problems, headaches or other symptoms, check if any troublesome microbes are hiding in the AC. This is especially important if you tend to sleep with your aircon on!

Frequently Asked Questions

Can bacteria grow in air conditioners?

If the air conditioner is not maintained and cleaned properly, there is a high chance of bacteria and mould growing inside it.

What are the symptoms of air conditioning sickness?

There are various symptoms of air conditioning sickness. Some of the symptoms are respiratory issues, nose or throat irritation, coughing and sneezing, fatigue and headaches, and sore muscles and joints. 

Can you get Legionnaires disease from home air conditioning?

The Legionella bacteria prefers freshwater bodies breeding grounds. Since home air conditioning units do not use water you are unlikely to get Legionnaires disease from them.

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