Jim Dillon
Barry,
I investigated this a few years ago before we installed AC. There is actually quite a bit of research available on this topic. Try searching in PubMed using the search words "ultraviolet disinfection of air" or something close. IIRC, what I concluded (right or wrongly) was that UVAC reduced the level of airborne contaminates by reducing (or preventing) the growth of contaminates at the source, i.e. the coils, drain pan etc. This is why most providers of this equipment (Honeywell, Aprilaire, Ultravation, Sterilaire) recommend that the bulbs be located adjacent to the coils, and not somewhere else in the duct system - because of the air-flow problem others mentioned. The only downside that I can recall (other than expense) is that the plastic on any exposed wires may deteriorate with time, and that the bulbs must be changed at one, two or three year intervals depending on how you are using the system. Hope this helps.

Jim