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Can you get Legionnaires’ Disease from Air Conditioning

30th May 2022

What is legionnaires’ disease?

Legionnaires’ disease is a respiratory disease which is contracted by inhaling legionella bacteria which can be found in water.

Can I get it from drinking water?

No, you can only get legionnaires’ disease by inhaling droplets of spray from evaporated water.

When am I at risk from inhaling droplets of spray?

When the water has lain stagnant over a long enough time for the concentration of the bacteria to reach a harmful level, this time being dependent on the temperature of the water being between 20-45°C. Outside this temperature range, the bacteria can’t multiply to a harmful level.

Is it possible to get legionella from air conditioning?

There is a potential risk with water cooled air conditioning, but not air cooled types.

What’s the difference between a water cooled and an air cooled system?

Water cooled systems are where the heat is rejected through a cooling tower. In air cooled systems the heat is rejected through a refrigerant condenser, not through water. Air conditioning with a comfort cooling application commonly found in offices and homes are usually air cooled systems.

Where is the risk in a water cooled system?

In the cooling tower, which has a reservoir of water, some of which evaporates into the air during a winter shutdown, the spray can be lethal when the system is re-started for the summer.

How can I prevent the risk?

By chemically treating the water supply to the cooling tower to kill the bacteria and, equally importantly, by regluar maintenance of the system, taking particular care during shutdown and start-up.

The air conditioning unit in my office uses refrigerant but there is water in the drip tray. Could legionella be found here?

No. This is just condensate from the dehumidification process and is pumped away. It is not at the right temperature to contain legionella and , even if it was, it can’t evaporate before being pumped away.

How common are cooling towers?

Cooling towers used to be very common before the use of air cooled refrigerant gases became more popular. They are still found in factories and public buildings but are becoming less common. 

What other areas in our business have a risk of legionella?

One area of risk are businesses that have showers which have been closed or out of order for any period of time. Before reopening, these businesses will need to ensure that their washrooms are suitably disinfected to eliminate any legionella risk.

How can I minimise the risk of legionella in these types of systems?

As with all air conditioning systems, cooling towers need regular maintenance. Your contractor can advise you on what procedures and steps they will take to maintain your air conditioning system.

How can I find out more?

If you need advice on your air conditioning systems please feel free to get in contact with us here.

For more information about air conditioning projects please take a look at our design and installation page.

For further information about our servicing and maintaining air conditioning take a look here.

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