Why Would I Need An Ultraviolet (UV) Light In My HVAC System? 

Mold Development

Mold likes an environment that is dark and damp and the inside of an HVAC system is dark and damp. Molds are micro-organisms that decompose dead, organic material that has made its way to the ducts or other landing sites within the system. The color of the surface upon which mold spores grow is often black or green. The color is determined by the type of mold in place, the nutrients that are feeding the spores, the type of material upon which the mold grows, and how long the mold has been growing.

Mold needs moisture, a food source, oxygen, and a held temperature between 40 and 100 degrees Fahrenheit. The mold will secrete liquids that are designed to decompose whatever substrate is there. Some molds can actually get humidity from the air if the relative humidity remains above 60%.

Mold multiplies and spreads by the use and extension of hyphae that act like root hairs. In this way, the mold can grow to cover a very large area inside the duct-work, coils, or drain-pan. The spores are carried away by air and water. When it reaches a new destination, it attaches itself to the substrate and begins the propagation process.

It is interesting to note that mold spores are always with us. They dwell outside and inside the home or building where we work. Mold becomes a problem when all factors are gathered together to produce a thriving colony. We are exposed to them all the time, but only when they have a food source and are being provided enough moisture and oxygen will they thrive and become a maintenance issue. What we have to think about is how to minimize the factors that cause molds to thrive. The primary factor to be controlled is the level of moisture present in the HVAC system. It is, therefore, important to understand that areas inside and outside the HVAC system need to be kept as dry as possible.

Health Effects of Mold

Mold spores and other contaminants live at the unseen, microscopic level. Because of this, humans have the tendency to think they are ok in their environments when they are not really. Exposure to mold can have serious health effects. Mold spores can cause nasal stuffiness, coughing, wheezing, eye irritation, throat irritation, and even skin irritations. People who have serious breathing issues before encountering mold will have even more difficult symptoms after encountering it. Mold exposure has been linked to the onset of pneumonia, asthma, and other deep lung conditions.

UV Light

Let’s take a look at what UV really is and what it means. The name comes from Ultraviolet which relies mainly on the “ultra” part to give it it’s defining qualities. As you may know, the light that we see is only a small portion of the kind of light given to us by the sun. “Ultra’s” original meaning in Latin was “beyond.” So, the light we are talking about is beyond the color spectrum of our human eye’s ability to see. It was discovered in 1801 and the research showed that ultraviolet light had the ability to react chemically with other components. In 1878, the light’s ability to sterilize bacteria became known.

Ultraviolet light uses a catalytic chemical reaction to produce the oxidation of organic matter. It is able to convert pathogens, pollens, and mold into harmless inert byproducts. Essentially, UV light can use a photochemical process to change contaminants into another chemical makeup. Because the contaminants are most often carbon-based, UV light can be helpful to break it down.

With better building products being developed, seals being covered with the latest sealants, and construction building codes focusing on better homes and buildings, the indoor air quality has declined. The air is usually re-circled and this air must be sent through filters. These filters have increased in quality over the years, but still do not remove all the contaminants in the flow of air. The installation of a UV lamp is a solution for eradicating harmful components of the air being breathed.


The most often location used for the installation of a UV light in an HVAC system is downstream of the air filter in the supply duct over and as near as possible to the intake side of the A/C evaporator coil. This location helps keep the lamp clean and targets the bacteria growth that may take place on or near the A/C coil. Another choice is to install the lamp in the return air duct downstream of the filter. A lamp may be placed in either location or in both.

Biohazards and Terrorism

It needs to be mentioned that UV lights are also being used in the protection of our population and reducing the impact of potential biological attacks on our homeland. UV has proven so helpful in the eradication and control of contaminated air that our Department of Homeland Security has commissioned laboratories across the nation to continue doing research directed at enhancing UV technology in homes, hospitals, public buildings, and government locations. Indeed, the Department of Homeland Security Research Center has joined with the Environmental Protection Agency to manage and encourage research into exactly how to keep American citizens safe if terrorists release toxic chemicals or airborne pathogens into atmospheric locations.

So, with the success of UV in home HVAC systems and with the use of UV as national protection against terrorists, the argument for the continued use of UV is pretty solid. The use of UV and its effectiveness is determined by the intensity and wavelength of the radiation, the length of time a microorganism is exposed to the light, and the type of contaminant present in the HVAC system. Even with these parameters and the growing types of contaminants present in the air, UV has data backing it up showing its usefulness in getting rid of airborne contaminants that harm people.