FWIW, the HVAC units installed in ducts in accordance to the instructions are designed to kill 99% of airborne contaminants on a single pass so long as the air is filtered of large particles and the bulbs and ballast are sized properly for the air flow and volume of the system they're installed in.
I did a LOT of research before I began messing with it. It is not to be taken lightly, so to speak.
The bulb/ballast combos for HVAC use are sized to compensate for the gradually diminishing output of UV-C that happens over time, so are factored into the bulb life ratings. But unless the bulbs are replaced annually (the exact schedule depends on actual hours of use) then they will become completely ineffective. And sizing for a custom build is not straightforward whereas HVAC specs are fairly standard and fall within a typical range of air volume and flow rate that the UV systems are specifically designed for.
IMO one way to look at UV-C in the context of mycology is thinking of it like a motion-sensing floodlight in the context of security. That is, it will add an additional layer of security to your property that might make a difference in some cases, but by itself it won't secure squat because to do that you'll still have to close and lock your gates on your fences and lock your doors and windows and all the rest before worrying about stuff like motion sensing lights.
A UV light is definitely not a magic bullet or miracle cure to contamination problems. But having one in my HVAC system has proven very beneficial to me over the years, so I'm still a fan and still keep one running.
If you really want to take cleanliness to the next level, get a commercial-duty high-pressure dry steam cleaner. Mine produces 65 PSI dry steam, which makes short work of pretty much anything organic and can sanitize the micro-scratches and pores found on even the smoothest surfaces and that liquid sanitizers cannot penetrate. Given a choice between having UV lights or a steam cleaner, I'd pick the steam cleaner without hesitation.
I did not intend to complicate the process of mastering mushroom growing, which is why all I was suggesting was installing a UV duct light in your HVAC system.