The faster the air flow, the less time the UV light has to work on a pollutant.

2) The indoor air pollutants must find there way into the air ducts. Due to air flow patterns in buildings most do not, but rather more readily find there way into the lungs of building occupants.

3) If air pollutants do happen to enter the air ducts, they must come within 2 to 6 inches of the light bulbs to be rendered non-viable. Most pollutants will not come this close to the light bulbs because of the interior size of the ducts.

4) The UV bulbs must be relatively new in order to be effective. The effectiveness of the light bulbs diminishes over time. Just because the bulbs light up does not mean that the bulbs are effectively working on air pollutants.

5) The area in the air return where they are installed does not offer any benefit in the A-coil area which is the most contaminated area in all ducted HVAC systems.

6) The daily operational cost of the UV is at least double that of technology which is not only effective inside the ducts but also covers the entire indoor environment.

Despite the fact that the old UV technology is still being merchandised by many heating contractors, these are a few of the reasons I don’t carry them through my company but prefer the UVX light spectrum in combination with radio catalytic ionization.