It bathes the area around it with UV-light, killing any bacteria and virus, along with some mold reduction, on the surfaces it shines on and also in the air it shines through. The technical term for it is “ultraviolet germicidal irradiation,” and it has only line-of-sight effectiveness. If the UV-light is not shining on a surface, then it will not be disinfected. 

   The photo above shows a unit manufactured by Honeywell installed in a supply air duct above an air conditioning air handler’s evaporator coils. When installed in this location, it treats both the surfaces of the evaporator coils and the air flowing through the duct. The photo below shows the same unit before installation.

    The system can also be installed in the return air duct to treat all incoming air in the air conditioning system. This particular UV-light system is activated by air flow in a duct.

    A UV air treatment system, in conjunction with an air filtration media, can be helpful for people with allergies or a compromised immune system and, when the evaporator coil area is irradiated, it can also reduce the musty smell emanating from a system with mold growth on wet surfaces by killing the mold. 

    Unfortunately, although a UV light can kill mold on the evaporator coil surfaces that it shines on directly and continuously, mold spores floating in the air through the evaporator coil are not exposed to the light long enough to have an effective kill rate. 

    UV air treatment devices come in many shapes and sizes, and the Honeywell unit is just one example. But, if you see a small  to medium-size box stuck on the side of a main supply or return duct near an air handler and it has the words “ultraviolet” on it along with a warning about not directly viewing the light, then it is likely a UV air treatment system.

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  To learn more about heating and air conditioning systems, see these other blog posts:

• How can I find out the SEER of my air conditioner? 

• My air conditioner won't turn on. What's wrong? 

• How can I find out the size of my air conditioner? 

• How can I tell whether the condenser (outdoor unit) is an air conditioner or heat pump? 

• Where is the air filter for my central air conditioner and furnace? I can’t find it? 

• Does an old air conditioner use more electricity as it ages? 

• How did homes stay cool in Florida before air conditioning? 

• What is wrong with an air conditioner when the air flow out of the vents is low?

• Why has the thermostat screen gone blank? 

• Why does it take so long to cool a house when an air conditioner has been off for a while? 

• Why is my air conditioner not cooling enough? 

• What are the most common problems with wall/window air conditioners?  

• Will closing doors reduce my heating and cooling costs? 

   Visit our HEATING AND AIR CONDITIONING page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.