Ultraviolet Lights (Benefits, Uses in HVAC, and Safety Precautions)

Thinking about installing Ultraviolet (“UV”) lights in your home for their alleged germ-killing benefits?

You’re in the right place!

In this proHVACinfo guide, you’ll learn:

  • What exactly is UV Light (can it really kill germs)?
  • Why everyone is talking about UV Lights (are these things the real deal?)
  • What the differences are between the different types of UV light (know what to look out for)
  • UV Lights in your home’s HVAC system
  • Top safety concerns of residential UV Lights and…
  • What the government think about this stuff
proHVACinfo | Ultraviolet Lights

UV light has been touted as “the next big thing” when it comes to indoor air quality (“IAQ”) control and air filtration, often praised for its alleged germicidal properties.

Moreover, with concerns about coronavirus running rampant for over a year, experts and homeowners alike have been looking at UV lights as a potential solution.

As a result, homeowners have happily paid hundreds of dollars to install fixtures inside their HVAC systems to put their minds as ease.

But are UV lights as good as they sound?

With our nation’s capital recently receiving a $600,000 grant to evaluate the effectiveness of UV lights on DC metro lines, you might think these devices are a cure-all for your microbial fears.

Let’s take a closer look at them shall we?

Each article on UV lights tends to copy the same supposed benefits over and over…

Seriously, check out the Google results for these things!

If you didn’t know any better you’d think that you should set up UV lights in every corner of your house!

And when used in residential HVAC systems, people are coughing up hundreds of dollars (sometimes more) in the hopes it’ll help keep them and their family safe of airborne pollutants.

The thing is…

In most instances, UV lights are, at best, not doing much of anything to disinfect your home. In fact, it’s more than likely you’ll end up using UV lights in a way that will damage other components of your HVAC system or that could even be detrimental to your health!

The truth is, yes, there is some evidence that under certain conditions, UV light can be beneficial, but if you’re going to spend your family’s monthly food budget on these things…

…then you should know exactly how they work and what their benefits are, right?

Our main Reason for Publishing this Article: Homeowner Knowledge and Safety

Right now there’s a lot of misleading, incomplete, out-of-context or biased information out there on UV lights, especially when to comes to HVAC.

This article is intended to lay out all the facts (from sources such as peer-reviewed articles and government studies) that exist on UV lights so you can make an informed decision, free of any confusing information or sales tactics.

Many of the websites that talk about the benefits of UV lights, especially when installed in your HVAC system, have a stake in the game.

They’re usually trying to sell you UV lights, and by the way, did they mention they can install them for you (for a steep fee, of course)? Not convinced?

Take a look at this forum post from an actual HVAC technician (from a post titled “Residential UV lights are worthless and potentially hazardous – Change my mind”)

Another professional HVAC technician on that same added that “The worst part is there will be dealers that will push the UV lamps […] playing on peoples fear of a virus only as a profit center, not an actual fix for anything.”

Don’t get us wrong – there are some HVAC companies / technicians that are doing right by consumers and correctly spelling out the limitations of their product offerings. However, as long as the individual advising you on the product is also selling it to you, there’s a risk of misaligned interests.

Here, we want to make all the facts available to homeowners from an unbiased source.

So, What Is UV Light Exactly?

There’s a good chance you’re familiar with the concept of UV light already.

The next time you’re headed to the pool on a hot summer day and reach for your favorite sunblock, take a look at the label and you’ll notice that the sunblock is rated according to how effective it is at protecting your skin from two different types of UV light, UV-A and UV-B light.

That’s right, the most common source of UV light is the sun!

What you probably didn’t know is that there’s a third type of UV light (UV-C), and that’s the specific type of UV light being touted around like it’s the best thing since sliced bread.

A Quick History Lesson

With all the rage about UV light in the media lately, you might think that using UV light to fight against dangerous microorganisms is a novel concept. However, the idea dates back the mid-1900s, when a Harvard University scientist by the name of William Wells demonstrated its effectiveness.

The scientific term for this process is called ultraviolet germicidal irradiation (often abbreviated as “UVGI”). In simple terms, what this means it that the light is used to disrupt the DNA of these microbes to kill or otherwise inactivate them.

As an aside, William Wells was the same scientist who discovered that airborne pathogens are introduced into the immediate environment from a cough or sneeze, and can then be inhaled by nearby individuals and get them sick (a concept we’re all-too familiar with in today’s world of COVID-19)! Remember William Wells – he’ll be important in a few minutes!

What Are the Different Types of UV Light?

Ultraviolet radiation (which, for our purposes, you can think of as the same as ultraviolet light) is a form of electromagnetic radiation.

Like all forms of electromagnetic radiation, ultraviolet light is made up of microscopic particles called photons. These photons move in a wave-like motion at various activity levels.

The scientific community categorizes the different types of electromagnetic radiation according to how active these photons are, and how long or short the length of the “wave” the photon creates is. This categorization is called the electromagnetic spectrum.

The photon wavelengths for all UV lights are between 10 and 400 nanometers (a nanometer is one billionth of a meter). More specifically: the breakout of UV-A, UV-B, and UV-C wavelengths are as-follows:

  • UV-A: 315 – 400 nanometers
  • UV-B: 280 – 315 nanometers
  • UV-C: 100 – 280 nanometers

This is important for you to understand because it’s important that any lights you consider installing in your HVAC system produce exclusively UV-C lights.

Remember our example with sunblock before? Sunblock protects against UV-A and UV-B light because those are the wavelengths that damage human skin, causing sunburns and even cancer after excessive exposure.

At this point, you might be wondering “wait, if UV-A and UV-B lights are so dangerous to my skin, why isn’t the same true for UV-C lights?”

The answer has to do with how the shorter wavelengths of the UV-C light interact with your skin. UV-C lights are absorbed by the outermost layer of your skin (which is dead skin anyway), and is unable to penetrate to the deeper layers of your skin like its UV-A and UV-B counterparts.

But keep in mind this is not the case for your eyes! The thing that protects your skin from UV-C light is the outermost layer of skin, which your eyes do not have!

So when it comes to the superficial tissues of the eye, UV-C radiation can cause damage similar to UV-A and UV-B radiation. For that reason, it’s crucial that any UV-C light installed in your home is properly installed such that you are never looking at it directly.

To put some numbers to it: one study conducted by Harvard public health scientists estimates that only about 5% of the most common UV-C light penetrates to the top viable cell layer of human skin, compared with 15% for UV-A light and 50% for UV-B light. The cells of the cornea have no such protective layer, which is why your eyes are at risk.

UV Light in HVAC

Today, UV lights have become the latest craze in the world of air purification, specifically when it comes to HVAC.

Typically, when homeowners have UV lights installed in their HVAC systems, they’re installed in one of two places:

  1. In the ductwork of the HVAC system: The idea here is straightforward. Install a UV light inside the supply duct (or in some instances, the return duct), near the source of the circulated air (near the furnace or AC, before the air’s been dispersed throughout the house). If UV-C lights were to work effectively, they’d kill any airborne particles traveling through the ductwork before making its way into the home
  2. At the cooling coil or drain pan of an air conditioning system: In this instance, the UV light fixture is installed such that light is directed inside the cooling coil / drain pan. The reason that this location is so popular is that the moisture and wet surfaces found in these parts of the HVAC system make a natural breeding ground for mold and other bacteria to grow. This mold and bacteria can shed contaminants into the air that can enter the HVAC system.

Why Everyone Loves UV Lights

It doesn’t take more than a quick Google search to find a number of website ready to talk about the alleged benefits of UV lights.

Some of the most common are:

  1. Kills Mold / Bacteria – As discussed, the number one reason everyone is talking about UV light is it supposed germicidal properties. We’ll get into more detail on this below, but for now we’ll just say that the actual science behind the application of UV lights in a residential setting is shaky to say the least.
  1. Improved Airflow – Microbes are not only hazardous to your health, but they can also build up throughout the HVAC system, making the various components work harder and reducing how much air can flow through the system. Removing the microbes would have the added benefit of increasing air circulation in the house.
  1. Improved Efficiency – Accompanying the increased airflow in the home is an increase in how efficiently your major HVAC components run (strictly speaking, the increased efficiency is what causes the improved airflow). As with improved electrical efficiency elsewhere in the house, what this would mean for you is that this would cut back on your electric bills. In fact, some articles go so far as to claim UV lights can cut energy consumption by up to 35%! As we’ll see, the reality is a little more nuanced, but it’s easy to see why such lofty promises can draw attention from eager homeowners.
  1. Easy Maintenance – In contrast to UV lights, the tried-and-true method to improve indoor air quality is by the use of a filter, especially a certified HEPA filter. The trouble with filters, however, is that over time they degrade, get clogged and need replaced (or at least, need regularly washed in the case of a washable filter). Compare that to a UV bulb, which can last up to 9,000 hours (about a year) before it needs replaced. Here again we see why UV lights have appeal for homeowners who just want to set it and forget it.
  1. Low Maintenance Cost – Less frequent replacement means lower maintenance costs once everything is set up. You can find replacement UV bulbs for around $30. Assuming the bulbs last a year, that’s about half the cost of replacement filters, which can cost around $30 for a 6-month supply.

So is UV Light Safe and Effective in your HVAC system?

Now that we have an understanding of the history and the science behind UV lights, we can get down to brass tacks.

If you do enough research on this topic, and spend hours poring through the actual scientific studies that are available (like we did), you come to realize a few things:

  1. The vast majority of articles out there touting UV lights have no scientific evidence to back up what they’re saying. The majority simply refer to anecdotal evidence, or accept what the broader community has established as fact.
  1. The few website that actually try to get at the science behind this stuff all boil down to the same handful of studies. The findings of these studies are often are then extrapolated upon in order to make convenient inferences about what could be possible based on related but ultimately inapplicable findings (inapplicable for our purposes, anyway).

You see, when you strip away all the fluff and focus on the facts at hand, the ability of ultraviolet light to kill airborne particles boils down to three things:

  1. Wavelength of the ultraviolet light
  2. Intensity of exposure
  3. Duration of exposure

Remember William Wells from earlier? Much of the recent work around the effectiveness of UV lights as germicide comes back to work he pioneered. Now, let’s revisit the science, taking each one of these factors into consideration.

Wavelength of the Ultraviolet Light

You already have a good understanding of the different wavelengths of UV light from the earlier section. That is, the most effective wavelengths fall into the UV-C category of 100 – 280 nm. However, not all light in this category is created equal! Work inspired by Wells helped further refine the specific wavelength broadly considered to be most effective as a germicide, and that is 254 nanometers.

Note: Some manufacturers are more precise, and specify their product uses the 253.7 nm wavelength. This is a relic of the specific type of measurements Wells and scientists back in the day used. Technically, the pioneering work was focused on wavelengths of 2,537 Angstrom, which is equivalent to 253.7 nanometers.

What this means for you is that in order to even be a candidate for use, a UV light must use the 254 nanometer wavelength. Anything else is ineffective at best and potentially harmful at worst.

Alright – enough of the technical stuff. Let’s get practical and look at two examples of Amazon products below, each of which are advertised as “Sanitizing UV lights and look similar on the surface.

Both these products are advertised similarly, as sanitizing UV lights, but thanks to what we’ve learned so far, we’re able to identify some problems.

As we see above, the second product not only doesn’t use the proper wavelength of UV light, it also produces ozone! More on ozone below, but believe us when we say any product producing ozone in your home is a major nonstarter.

More recent studies are being done on even shorter UV light wavelengths, specifically 222nm (which calls into the category of “Far UV-C” light). While there is evidence that certain wavelengths may be easier on the eyes and skin, other studies have shown that 222nm can still damage human skin (and, it would stand to reason, eyes as well).

There are a few websites out there selling “Far UV-C” light, but even those sites often include disclaimers that until more research is done, there is no guarantee that Far UV-C light is not potentially harmful.

Intensity and Duration of Exposure

Modern UV lamps will keep the intensity of exposure constant, so we’ll focus on duration of exposure in this section.

You see, the studies Wells is most famously known for don’t actually have anything to do with sanitizing rapidly moving air, like what would be needed in an HVAC system. His work primarily dealt with 1) preventing infections from airborne contaminants in hospital settings and 2) preventing the spread of common diseases (such as tuberculosis) among school age students in classrooms.

In the hospital setting, you can imagine UV lights hanging from the ceiling of an operating room, shining down across the floor, tables, and other surfaces in the room for hours on end, while the bacteria below bake in the germicidal light.

In the classroom setting, wells employed a sanitation method called upper-room ultraviolet germicidal irradiation (“Upper-room UVGI”). Upper-room UVGI is essentially the process of directing ultraviolent lights at the ceiling of a (sufficiently large) room with the intent of rendering airborne particles harmless after repeated exposure to the lights as the result of natural air circulation.

What this means is that every time these airborne pathogens circulated up to the ceiling of the classroom they got a strong hit of UV-C light. The cumulative exposure time of this recurring circulation is significant enough that it did help prevent germs from spreading in this scenario.

If you contrast the above examples in a hospital setting or in a classroom with the air circulation in your home’s HVAC system, the problem becomes obvious: the air circulating throughout your home’s ductwork would be exposed to UV light for no more than a second or two before it’s blown throughout the system.

A 2008 study estimates that UV light was effective in rendering bacteria inactive only after 30 minutes! This is realistic in a hospital setting or through repeated exposure in a classroom, but would virtually never happen in residential HVAC. Unfortunately, Far UV-C light seems to have the same problem.

While research is ongoing, one study suggested 90% effectiveness after 8 minutes of exposure time and 99.9% only after 25 minutes, both of which are unrealistic circumstances when it comes to residential HVAC.

Downsides of UV light

Now that we’ve looked under the hood of some of the common factoids about UV lights and seen that they aren’t all they’re cracked up to be, let’s consider some of the downsides when it comes to UV light.

Anything that’s covered in shadow is not affected

When we think of UV light in an air duct, we tend to imagine the light touching every corner of the ductwork, instantly affecting anything that passes through, like a force field. Unfortunately the reality is more complicated than that.

The reality is that many common airborne pollutants, including viruses, can actually travel through the air while attached to dust, fibers and other microscopic particles.

Recent research found that viruses can be transferred when attached to fur as well as microscopic fibers inanimate objects.

One of the well-known limitations of UV lights is that in order for the lights to be effective, the light must directly hit the pathogen it’s trying to destroy. That is to say, anything covered by a shadow is not affected by the light.

What this means is that any microbe attached to larger (but still microscopic) particles could easily elude any effect at all from UV light.

This is a known limitation of using UV light even in the relatively stable context of a hospital room, where shadows abound. This is less of an issue for something like upper-room UVGI, where particles are consistently floating around.

However, contrast that with just the second or two any airborne particles are traveling through your HVAC system, and we see that the truth is far from the “force field’ of air quality protection we like to imagine.

Ozone

As we saw in the example Amazon product above, manufacturers (and sometime in-person salespeople) are often eager to sell you anything they can justify calling “sanitizing UV light” as though all products are created equal.

In some instances, this can mean selling you a product that not only is ineffective (because it uses the wrong UV wavelength), but can also mean selling you a product that introduces ozone into the air you breathe.

Why is this a problem?

Thanks to the EPA, it’s no secret that ozone is bad stuff when introduced into your home and the air you breathe. Ozone can damage your lungs, irritate your thought and cause coughing, chest pain, and shortness of breath.

There is a longstanding issue in the field of indoor air quality of sellers advertising “ozone generators” as a helpful piece of technology to cleanse the air, when the reality is that they’re anything but. While this topic is largely outside the scope of this article, it illustrates the issue that it can be extremely difficult to know what you’re actually getting in the area of UV light, and the person selling it to you might not know either!

This is the same reason why at proHVACinfo we never recommend any products that produce ozone.

For the sake of completeness we’ll mention that the negative effects of ozone can be mitigated by certain types of glass used for the UV light’s bulb, but for simplicity we’ll just say here that if you do choose to get a UV light, be sure to get one that doesn’t product any ozone!

Damage to materials

In addition to the potential ozone exposure, there is risk that UV lights will degrade and even damage certain materials, including plastic, polymers and certain dried textiles. What this means in practical terms is that there’s a chance the UV light you’re paying so much money for could be not only ineffective, but could actually damage the casing on the wires in your HVAC system as well as air filters.

Let’s take a look at what yet another HVAC technician had to say

What Does the Government Think About UV Light in HVAC?

While the government doesn’t explicitly discuss UV light in the context of residential HVAC, there is some information about whether UV light could be used to fight coronavirus; information available on various government websites is consistent with what we’re talked about above.

The FDA website is quick to point out that work still needs to be done about the most effective wavelength, dose and duration of UV-C radiation required to fight coronavirus (they also cite UV lights’ use in reducing the spread of tuberculosis, no doubt a reference to our friend William Wells!)

It also confirms that UV-C radiation is only potentially effective after direct exposure, so viruses covered in shadow buy other contaminants such as dust will shield pathogens from any would-be effect of UV light.

Furthermore, the FDA confirms many of the risks identified above, including potential harm due to direct exposure to skin and eyes, the potential for UV-C lamps to generate ozone, degradation of household materials, and even the potential for some UV-C lamps to contain mercury!

What Should You Do Instead?

Now you might be thinking “Great, you’ve convinced me that UV lights aren’t all they’re cracked up to be. All I want to do is keep the air my family and I breathe safe. What should I do instead?”

This is a great question. The good news is that the principles for maintaining high indoor air quality have been well established for a long time and haven’t changed. The bad news is that it doesn’t have to do with the latest craze or any fancy technology.

The three principles for indoor air quality were already mentioned by our first HVAC technician above who was skeptical of UV lights. They are: ventilation, humidity control, and filtration.

Ventilation

The EPA has long said that the single most effective way to improve the quality of your indoor air is to ventilate your home with clean outdoor air.

This is a decision you have to consciously make and a step you have to actively take because most home heating and cooling systems do not mechanically bring fresh air into the home (i.e. they don’t have an outdoor air intake).

The good news is that this step is very easily accomplished by simple things like opening your windows or cracking a door.

This has the added benefit of not only introducing clean outdoor air into the home, but also diluting the concentration of any airborne pathogens that might be inside already.

Humidity Control

Humidity control is an often overlooked component of indoor air quality.

What most homeowners don’t know is that indoor humidity can increase concentrations of certain indoor air pollutants, including mold. If mold beings to grow, it can produce spores that can irritate or otherwise damage the lungs.

The ideal level for indoor humidity is between 30 and 50 percent. Simply opening the windows (if it isn’t humid out) or turning on the air conditioner (if it is humid out) can help decrease humidity, while a whole-house humidifier can increase humidity.

Filtration

The last component of effective indoor air quality is filtration. By this we mean the use of portable air sanitizers (air purifiers) where needed in the home and an effective furnace humidifier.

The Bottom Line: (be very careful when dealing with UV lights)

At the end of the day, the main reason we wrote this article and have been so critical is that while UV-C lights are being touted by some as the next generation product for residential indoor air quality solutions, the truth is that the jury is still out and there are real risks that are understated or are often ignored entirely.

For example: when a website or overly-aggressive salesman tells you they’re offering a next-generation product that uses the latest technology to stop any airborne pathogen from entering the air you breathe, what else would a homeowner who’s simply concerned for the wellbeing of their family do but justify spending hundreds of dollars on something to keep their family safe?

The next thing you know, you have these fixtures homeowners don’t fully understand installed throughout the house, potentially around young children, emitting light that’s could be hazardous to the eyes and skin or even introducing ozone and mercury into the home environment.

This article should be reason enough for you to think twice before spending that amount of money on something so scientifically dubious.

On the other hand, say you’re someone who’s just all-in on the idea of UV light for cleaning your home, and you’re ready to pay whatever it costs right now to get these things set up? In that case, we hope this article has given you the information to make the right decision, so you know exactly what to look out for and, more importantly, what to avoid.

Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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Stephen Marks

Stephen Marks

Stephen is an HVAC and home-repair enthusiast. He's here to answer any of your questions about HVAC!

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