Ventilation is not the same as air conditioning.

In some buildings mechanical ventilation systems also provide heat and cooling, but in others stand-alone air-conditioning units are installed to cool the air – these are very common in offices and hospitality buildings.

Mechanical ventilation systems work by providing fresh air to a building via ducts and fans and/or extracting stale air from rooms. There are a range of different systems, from simple extractor fans to interconnected systems serving multiple rooms. The performance of a system will depend on its design and the maintenance, as well as whether the flow rate of the ventilation is suitable for the number of people in the room.

Most stand-alone units do not provide any fresh air, and so they do not reduce the risk of infection – in fact they can give a false sense of security by making the air feel fresh when it is not.

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