How To Install An HVAC UV Light (5 Step Guide)

Are you interested in learning how to install a sanitizing UV light inside of your HVAC?

You are in the right place because even hospitals use UV-C light to disinfect medical equipment and operating rooms (here is my review on the best UV lights to kill mold).

I created this step-by-step guide on how to install a UV light to keep your A/C system free from mold and mildew protecting your air quality. 

In this article, you will learn...

how to install uv light for hvac
  • Why you should never allow a UV light to shine on your eyes or skin (a safety hazard)
  • How to determine the best location to place the UV light
  • How to use a hole saw to cut into the metal duct (and my top hole saw choice)
  • The best way to power a germicidal UV light unit
  • Important things to do before installing a UV light (if there is already mold)

Let's get started with this guide!

Read Also: The Top 5 Best UV Lights For HVAC

The Five Steps To An HVAC UV Light Installation


#1. Choose Where To Install The UV Light

​​​​Perhaps the most important step is to choose where to install the UV light. You want it installed where it will be most effective and kill the most mold and mildew.


#2. Drill The Hole(s) For The UV Light

​​The biggest physical step is drilling the holes in the metal HVAC cover so that the UV light bulb can be inserted. Most holes will be 1-1/2" to 2-1/2" in diameter.​​


#3. Screw The Germicidal UV Light To The Furnace

In this step, you take screws and secure the UV light housing to the air conditioner. You don't want to tighten the screws too much where you damage the plastic housing.


#4. Power The A/C UV Light System

After the UV light is secured, you will want to add power to the UV light. Usually (and the easiest) is to just plug the UV light into a regular 120-volt outlet.


#5. Change & Clean The UV Light Bulb

After it is installed, the only real maintenance is to change the bulb annually (or at most every two years) and clean the light bulbs seasonally.

#1. Choose Where To Install The UV Light

The first step in installing a UV furnace light is to determine the best location on your furnace or air handler. If the germicidal UV light is installed in the wrong place, it will greatly reduce its effectiveness in preventing mold or mildew growth. 

Usually, you want to install the A/C ultraviolet light treatment system so that the evaporator coil gets the most amount of light. According to Lincoln Tech, it is the evaporator coil (and drip pan) that is usually the source of HVAC contaminants.

The evaporator coil is susceptible to the growth of biofilms which are communities of microorganisms that stick together on a surface. The amount of surface area of an evaporator coil is around 5,000 square feet.

The evaporator or A-coil is the part of the air handler that has the copper (or aluminum) tubing where the refrigerant runs through. It frequently has the shape of a tepee or "A" and frequently has the most dust buildup and mold growth.

evaporator coil shape (3)

However, if you have already had mold growth in your HVAC and there is a particular corner or area of the air handler that is prone to mold ---- then you should install the UV light so that it shines the most on the problematic mold area. There is no point in experimenting with locations if you already know that one spot of your A/C gets the most mold growth.​​

A-Shaped Evaporator Coil

The best location to install a UV light if in the A-shape is above, center, and downstream of the coil. This allows the A/C ultraviolet light to shine the most amount of light on the coil, while killing some of the airborne microbes.

The second best location is below the evaporator coil (if there is room). If none of these locations are feasible, then you can install the UV furnace light to either side of the coil.

Diagonal Shaped Evaporator Coil

If the evaporator coil is a diagonal shape, then there are only two options. You can either install the light above the coil or below it. Preferably, you should install the UV light closer to the drip pan and where there will be more moisture.​​

If you don't feel like the air handler is getting enough UV light, you can always install an extra UV light in a different location.

Professional Installation

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#2. Drill The Hole(s) For The UV Light

The next step is to drill a hole (or two) into the indoor air handler so that the UV light bulb can penetrate inside the unit. All UV light sanitizing systems are installed so that the main part of the product is mounted to the outside, while only the long ultraviolet light bulbs enter inside.

Take Measurements Before Drilling Holes

It is advisable to remove the cover to the furnace, and take some measurements. You don’t want to drill a hole in the sheet metal only to find out that the location won’t fit for the UV light bulb. You can also just carefully insert the UV light bulb in the location where it will be installed to get an idea that it will fit correctly.

Pro Tip:  Don't ever touch the A/C UV light bulb. The oils from your skill will reduce the light of the bulb and may damage it.

Using A Hole Saw Drill Bit

Some HVAC UV light systems come with everything you will need to install a UV light--- including the hole saw drill bit---except of course an electric drill. If you bought a UV light without a hole saw, you will need to buy one so that you can cut a circular hole through the metal HVAC cover (or ductwork). Most UV lights will need either a hole in the range of 1.5" to 3" in diameter.

Shut Off Power & Use Paper Template

It is important to first shutoff the power to the HVAC system before installing a UV light---you don’t want to accidentally get shocked. Locate the breaker at the panel box, and flip the switch.

Most AC UV light products will come with a paper template for the mounting. Tape the template to the area where you wish to install the UV light. The template will help you cut the holes at the proper distance apart (if there are two bulbs).

Start slowly as you cut into the sheet metal, and as the hole saw makes a small groove, gradually push the saw into the ductwork to cut the hole. It may help to rock the drill bit back and forth to get a more effective cut.

does uv light kill mold in hospitals

#3. Screw The Germicidal UV Light To The Furnace

The third step is to screw the UV light to the air handler. The UV product should of come with a few screws for the install.  Simply use a cordless drill or a phillips screwdriver to secure the UV light to the metal.

Make sure not to install the screws too tightly where it may crack the plastic of the UV light. As a reminder, do not plug in the UV light bulb before it is fully installed. The UV light can burn your skin and may damage your eyes.

#4. Power The A/C UV Light System

With the UV light sanitizer secured to the furnace, now you want to power the system. Most new UV lights will come with 5′-7′ long extension power cords. All you will need to do is plug the unit into an existing outlet. Most utility rooms will already have an outlet. 

Another option is to hardwire the UV light into the furnace. You can even wire it so that the UV light only turns on when the furnace or A/C turns on so it isn't on 24 hours. Hiring an electrician or HVAC contractor to do any custom electrical work is recommended.

After you have plugged in the UV light, simply flip the power switch on the unit, and check the sight glass to make sure that the UV light is actually on. There should be a bluish glow in the sight glass.

#5. Change & Clean The UV Light Bulb

Most UV light bulbs will last about one year. If there is blue light shining, this doesn’t mean that the bulb doesn’t need replacement. The actual UV-C frequency that kills mold is invisible to humans. There may be blue light emanating from the unit, but it is no longer shining enough UV-C light frequency.

It is also recommended to clean the UV light bulb every few months or after every season. To clean the unit, you will need to take out the bulb, and clean it with a soft lint-free cloth such as a microfiber rag. You can use regular glass cleaning solution to clean the bulb from dust and debris.

Read Also: Does UV Light Kill Mold? (How Effective?)

What's The Bottom Line On A UV Light Installation For The HVAC?

If you follow the steps in this guide, it shouldn't be too difficult to install a UV light to kill mold and mildew in your indoor air handler.  The basic idea is to cut a hole in the best location, insert the bulb, use screws to secure the light, and plug it in.

If you have all of the supplies, you should be able to install a UV light within 15min to 30min. However, if you want to hardwire the UV light to your furnaces power, it may take longer. Other than that option, using the hole saw to cut the hole(s) will likely be the most challenging aspect of a UV light install.

I would recommend purchasing a quality hole saw and a powerful electric drill to make the hole cutout much easier.

Other Home Guides

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company. To ask Arie a question, please use the comment box at the bottom of the relevant article.

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