IINM, listeria is usually spread by contaminated food, not air.

Probably meant Legionnaires. Melbourne recently had an outbreak when outdoor cafes used cooling towers (essentially mist sprayers) with some sus water - https://www.health.vic.gov.au/health-alerts/outbreak-of-legi...

My bad. Yes, I saw DIY heat exchangers posted in the past and people were worried about Legionella/Legionnaires and mold. It seems scary when we don't know what we are doing.

DIY heat exchangers would be so awesome though. Only new constructions are required to have an heat exchanger here.