IAQ and Air Cleaners

We get questions all the time regarding the use of UV lights in residential HVAC units. Where is the best place to position one? How do they work? What is the best use of them?

For a time, Aprilaire offered our own line of UV products. Our recommendation was always to position UV lights near the peak of your A/C’s evaporative coil or “A” coil. Place it in such a way that the coil and drain pan are fully expose to the light. These are the components most likely to contribute to microbial growth as they contain the three things most needed to support it, moisture, a food source, and a dark environment. Plus, even if your home has a whole-house air cleaner, anything growing on your A-coil can enter your air stream after the air cleaner.

Conversely, UV light is not terribly effective as an air cleaner for several reasons. The first is a question of exposure. Particles tend to zip through your air ducts at around 300 feet per minute. What this means is that their actual exposure time is a fraction of what would be required to destroy organic particles. Put another way, if you were baking cookies in your oven (oatmeal raisin, of course) you might be able to tap the edge of the hot baking sheet without getting burned, but if you held your hand there, you would definitely get a serious injury. The concept is the same with UV light. Most particles require a minimum amount of exposure to be considered destroyed, and this can be from a few seconds to a few minutes. And in order to get that exposure time, a particle would have to zip in front of a UV lamp many times. Hopefully, there’s an actual air cleaner on your system to trap those particles so that they don’t get a second chance to zip through your ducts. They would get trapped the first time.

The second reason is simply that, with an air cleaner, once that air cleaner has trapped the particle, destroying it is a little redundant. If an organic particle can’t get back into the air stream, does it matter if it’s alive or dead? Generally not.

So there we go.