Hi, Mike

The use of UV light for deactivating bacteria, viruses, etc. isn't new. I had UV lights installed in two HVAC systems in my former home 20 years ago. They were part of the Lennox "Pure Air" system.

There are two applications for UV light in an HVAC system: air sterilization and coil sterilization. According to what I've read, UV light is more effective for deactivating microbes and viruses on surfaces than in the air stream because of the amount of exposure time required to deactivate them. So, from a practical standpoint, I suggest the use of UV light is limited to coil sterilization.

Before spending money on a UV disinfection system, I suggest you consider alternatives which enhance air filtration, and install a continuous fresh air ventilation system with energy recovery such as an ERV or HRV. While those won't remove 100% of particulates, bacteria, and viruses, they will reduce their concentration in air and provide a general improvement in indoor air quality 24/7.

I think for residential they're basically snake oil.

My understanding is that gaining any benefit from UV in the airstream requires an enormous amount of power and a quite expensive UV system. As @Charles Ross Homes said, they can be effective on the coils but I'd guess that the majority of coils still wouldn't benefit from them as you'd be trying to kill something that's not there.

Yes to a proper ERV/HRV!

See what MERV filter you can use in your installed HVAC system if its forced air. We run MERV-13 (that does well against most pathogens including COVID) as a standard filter but have MERV-16's for when outside air quality is really bad (typicallly forrest fires).

Our HVAC blowers are constantly ON (not circulate which typically only runs 20 mins per hour) and our ERV's run for 20 mins / hr standard but also any time CO2 levels are above 550 ppm.

I agree with Charles: "the use of UV light is limited to coil sterilization" in domestic HVAC systems. UV light in a static environment (anti-bacterial hood, HVAC coil) may kill bacteria under the right conditions. In a dynamic setting (in a heating/cooling air duct) the airflow is to high for the UV to have time to kill anything. Plus, you have to change the bulbs every year (and they aren't cheap)!

Oh, and its amazing how companies take advantages of bad information in pandemics ("Almost daily we are out at schools, hospitals, nursing homes and doctors offices installing these")!