Ultraviolet Air Purification, Before You Buy... 

An understanding of ultraviolet air purification can save you a lot of money. There are many of these products on the market today. Most of the products are no better than the snake oils that were peddled in the early days of the U.S.A.

These products are designed to kill germs, viruses, and other micro-organisms. They use a process called photocatalytic oxidation to attack the dna of these pollutants. 

This process involves the use of an ultraviolet light bulb. Their ability to kill the organisms depends on the strength of the UV field and the amount of time the organisms are in that field. Although the process can kill organisms, it is not the most effective means of improving indoor air quality. The airflows in a typical home hvac system do not allow the organisms to stay in the UV field long enough to be killed. Also, these units do not physically remove the organisms from the home.

Disadvantages of these units... 

There are several disadvantages of using these products. They are expensive to buy and to maintain. The bulb requires replacement every year and they are not cheap. Also, the bulbs contain mercury which is bad for the environment. It is recommended that special precautions be taken to dispose of them.

Furthermore, the UVc rays can degrade plastic materials. (Most of the evaporators in newer central ac systems have a drain pan that is made of plastic.)

Ultraviolet Air Purification, Better alternatives... 

There are much better air purification methods. One simple alternative is to upgrade the filter in the hvac system to a MERV 10 air filter. This is as effective as the light and a lot less expensive. They also actually trap the organisms and they are physically removed when the filter is changed.

Along with replacing your filter, a properly designed duct system is an effective solution in place of the air purifier. It is less expensive and more effective to lower the concentration by dilution with outside air.