Most air conditioning is not a legionella risk
Typical split units, cassette units and car air conditioning cool air using refrigerant, not sprayed water. They do not create the fine water droplets needed to spread legionella. Condensate trays should still be kept clean and draining.
Where the risk is real
- Cooling towers and evaporative condensers, which reject heat by evaporating water into the air
- Evaporative (adiabatic) coolers, which cool air by passing it through wet pads or sprays
- Humidifiers that create a water spray or mist
These systems have been linked to outbreaks and are covered by HSG274 Parts 1 and 3.
What to do
If your building has any of these systems, it needs a specific risk assessment and a written scheme of treatment, monitoring and cleaning. See our cooling tower service and HSG274 Part 1 guide.
Frequently asked questions
Can a split air conditioning unit spread legionella?
Standard split units do not spray water into the air, so they are not generally considered a legionella risk. Keep condensate trays clean and draining.
Do cooling towers spread legionella?
They can if poorly managed, which is why they must be notified to the local authority and treated, monitored and cleaned under HSG274 Part 1.
Disclaimer: This guide is general information about UK requirements and is not legal advice. Always check the current legislation and guidance for your premises.