When to replace UV-C Lamps in your HVAC System

Installed in your facility’s AHU plenum or HVAC ducting is a UV-C lamp which, depending on the condition, may or may not be performing its primary disinfection function. Researchers believe eight out of 10 building engineers forget to replace their facility’s UV-C Lamps at scheduled intervals, meaning that 80% of facility managers are not seeing the ROI on their germicidal UV-C equipment.


UV-C lamps, while typically thought of as mysterious, are in fact manufactured on the same types of machines as fluorescent lamps and operate identically.


ABOVE, The left UV-C bulb looks nearly identical to the standard fluorescent lamp


The difference is that UV-C lamps require doped quartz glass, an expensive type of glass that does not include the internal phosphor that makes fluorescent lamps glow, producing visible light. In other words, because the UV-C wavelength (253.7 nm) is invisible to the human eye, the blue light that we can see only represents 5% of the total output of the lamps. So you can’t see if the remaining 95% output is reading full or empty. Unlike the dark or flickering lamp above your desk, the visible light emitted from a UV-C lamp is not a useful indicator of its performance. In short, UV lamps will continue to emit the blue light long after the UV-C output has decreased, by even more than 50%!

ABOVE, The UV-C wavelength (253.7 nm) is invisible to the human eye, the blue light that we can see only represents 5% of the total output of the lamps.



UV-C fixture design, while similar to fluorescent fixtures, is different in a number of ways. One of the primary differences is the environment in which these HVAC type fixtures are meant to operate. Its stainless steel construction is one of the main differentiators; however, the functional life difference has to be its electronic ballast design. Being in a cold, damp environment requires a robust ballast that can withstand the fluctuating electrical demands of the lamp as its surrounding air cools, warms and moves. Also, the damp environment provides an additional challenge for the electronic components and necessitates the use of a complete waterproofing, or that it can be mounted remotely, outside of the plenum.


ABOVE, The benefits of using germicidal UV are two-pronged: clean, healthier air in your building and a cleaner, healthier HVAC system (which means less maintenance, odours, and an overall longer-lasting system).


The applications of UV-C lamps are many, they are used in virtually all building types for HVAC surface irradiation to keep cooling coils and plenums clean.

Another popular use since the 1940s is upper-air UVGI systems for in-room killing of airborne pathogens. In all cases, maintaining the lamps so that the installed systems are emitting the proper amount of UV-C energy to accomplish the goal of the application, is imperative.

Most lamp manufacturers (American Ultraviolet, Sanuvox, Phillips, Steril-Aire, GE, etc.) recommend: removing and replacing UV lamps every 9,000 hours or 1 year (annual preventative maintenance [PM] schedule). Most premium quality lamps will emit at least 80% of their original UV-C output at the end of one year.


Premium quality lamps will emit at least 80% of their original UV-C output at the end of one year.


An annual schedule consolidates change-outs into one service interval, allowing the facility to purchase lamps in larger quantities, saving time and costs.
In remote systems (mechanical rooms, interstitial spaces), there are accessories available for continuous monitoring of lamp-ballast functionality that communicate with building management systems (BMS). Monitoring of critical environments (hospital isolation rooms, etc.) for whole system performance and lamp-on hour meters can be utilised as well.


ABOVE, Direct human exposure to UV radiation is extremely dangerous. Viewing through a UV-C viewport is the safest way to view fixture operation – the safety glass blocks UV-C bandwidth light.


The locations where UV-C fixtures are typically applied have unfortunately created a situation where the lamps are installed and often forgotten.  Later on Facility Management may believe they work when in actuality, the lamp’s lifespan has expired. Whether UV-C fixtures are installed at the air handler manufacturer’s factory or retrofitted into an existing system, when UV-C is installed, it should be immediately added to the building's PPM programs. This way it’s not forgotten and its benefits can be enjoyed for many years to come.


when UV-C is installed, it should be immediately added to the building's PPM programs. This way it’s not forgotten



When it comes to replacing UV-C lamps, certain practices should be avoided. A common mistake many make is replacing them only as they stop functioning. This method is highly labor intensive and inefficient. Furthermore, as that 9,000-hour mark passes, the lamps’ germicidal effectiveness begins to diminish, potentially causing HVAC system performance to be compromised.


ABOVE, No matter how good the coil cleaner, sprayer or pressure washer used, the effectiveness of these methods reaches about 30mm into the coil and the organic and biologically active matter gets packed deeper into the coil fins.


A more advisable solution is to establish an annual replacement schedule whereby all lamps are methodically swapped out at a designated interval. Such a strategy eliminates the need to carry a large inventory of replacement lamps. Instead, it offers plenty of lead time and a more logical routine. Annual replacement is also more cost-effective. Individual replacement means higher lamp and labor costs and downtime during each procedure. An annual schedule consolidates change-outs into one service interval. This also reduces the need, with the exception of critical environments, to invest in an expensive radiometer or other equipment to monitor individual UV-C output. The knowledge that lamp replacement will be serviced each year will allow peace of mind for Facility Managers.


Most important of all, annual replacement guarantees that UV-C output will never fall below effective levels and HVAC/R efficiency and IAQ will not be compromised. By implementing such a schedule, you are doing your duty to protect both your building occupants, as well as your equipment from the effects of microbial buildup.



Enjoying the read? Learn more about UV-C here at cleanairaust.com.au/uvc, or email the team sales@cleanairaust.com.au, we’re always on hand to offer specialist solutions and detailed analysis of your HVAC-R Systems.