I see many new offering from HVAC companies to do retrofit UV lights on AC systems as a way to combat the coronavirus.

I also see a number of ads from local establishments like restaurants, hair salons etc... claiming that they have new "coronavirus killing UV systems in place to make sure their environment are sterile".

I also see some reports saying that UV-C doesn't do much because it needs time to work and the air is moving through the AC too fast for it to have any real effect.

Anyone knows for sure? I could use a Myth Buster eposide on this.

 

It all depends... Yes, UV can kill virus, bacteria and mold. But, it must be of sufficient intensity and there must be enough exposure time. Higher intensity of UV requires less contact time and vice versa so you can't simply say "it works" or "it doesn't without examining all the parameters. The system must be designed and sized properly in order to work. Also, UV bulbs decrease in output as they age so they need scheduled replacement.

I have used UV sterilization with my aquariums for decades. It even works on larger organisms and algae. I had to match the power of the UV sterilizer to the flow of water I put through it. But once you get it set up properly it does work.

 

At the current time they don't know if the HVAC system can spread corona virus. There are no documented cases of that happening. Typically UV/C in the air handler is installed close to the evaporator coil to help control mold buildup on the coil.