Exposure time, and dust. IMO UV is not at this point overly practical for most home heating/cooling systems.
This is the site & info that we use at work. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
Filtration / Disinfection (ashrae.org)
My reason for posting filter info, was for those caught up in the wildfires.
In those cases, such as millions of people in North America (and elsewhere) are currently in, it doesn't matter one wit whether you live alone, or not. Unless you enjoy the taste of wildfire smoke.
Hello; Interesting take on the UV sanitizer lights. We have for months been wearing make do masks because the good stuff was near impossible to find. I get that the good masks were for you medical workers. Some sense in that. However the masks I could find the last months were just a little better than nothing to somewhat better than nothing. So that the UV lights are not practical enough for home heating/cooling is an odd take. First they have to be some better than nothing which seems to be a standard good enough so that masks are mandated again in many places.
I again assert that an authority which mandates wearing a mask ought to have a decent mask available, but that is just my ignorant way of thinking. But such is a side issue.
I also did not limit my comment on UV lights to home use only. I did use the word buildings for a reason. Some folks live in an apartment complex with central air. I did for a year. Some other buildings where people work may have separate offices and rooms but have shared air. I rented a room in a mans house for two school terms years ago. I guess I figure if the UV works to some extent then they may be worth it to some. The cost would be less in the long run than replacing the expensive filters. Folks could do filters and UV lights for all I care. I just personally live alone in a house so it is not an issues for me.
Hello; Yes the smoke is a problem for anyone with breathing problems. I can see how having a lung affecting virus and having to breathe smoke is a problem. Same as being obese, having asthma, and other side issues can be a problem. Including my high BP. A UV light may not do anything for smoke but if one can keep virus levels down then why not. If I wind up in a nursing home and have any say so the building will have a UV system.