Comment by vbelenky

Nah--use 254nm for that. It's a standard thing, if it's contained in a duct it doesn't need to be fancypants human-safe 222nm.

Ducting it kills most of the effectiveness though--now you have to move air through your ducts in order to treat it, so you only get as much treatment as you move air--usually not very fast or else it would be loud and annoying. You can move it faster, but then you need more UV since the faster-moving air won't be exposed for as long. Honestly, upgrade to a MERV-13 filter before thinking about residential in-duct UV

In-room UV is a different story--since it exposes all room air, pathogens start getting inactivated as soon as they're exhaled. The whole room becomes a disinfection reactor.