I am adding a UV light to my furnace coils. I decided to cut an access panel for easier cleaning and access to the UV light. I did not realize there were these triangular end covers for the A-frame of the furnace evaporator coils.

I don’t see them anywhere online when looking up diagrams of furnace coils. When I search online, it is also not clear if these covers are necessary. Are these covers beneficial? Or can I take one side off to fit the UV light underneath the A-frame?

It looks like without them air will go around the coils rather than through them, but I'd need to see more of the system to be sure.

There's about a 2" gap from the cover to the side of the duct - lots of air will simply bypass the coils.

I’m no hvac expert, but if you change the way the air flows by removing it, those filters are going to be pointless.

I’m no expert, but I am handy.

I called my HVAC technician before, and he told me to install mine in the chamber after that one. I have one before it splits.

Call your HVAC technician and ask them for over the phone advice. My tech offered to install mine for free on my next service.

I still did mine, and he checked my work and okayed it as “a gold star install.”

Here is a picture after I installed it and before wiring it.

Edit:
I don’t have a finished photo, but I will post one on request. I’m too lazy to take a photo and explain why if my wife asks.

It's only necessary if you want your furnace to heat the air. Without it, air will simply take the path of least resistance and bypass the coils entirely.

My friend finally got back to me and said the same thing. I guess I learned something about furnace coils. I ended up making a compromise and just mounting the light into that end plate.

What do you mean by “ before it splits?” I’m still learning a lot, but the general consensus of where to place the UV light was on the bottom side of the A-frame, because that’s where the moisture will accumulate and allow for bacteria and fungus growth.

I ended up drilling a hole and mounting the light right into that end plate, and then drilling another hole in my new access panel for the cord, and putting duct putty around the hole.

Thank you, that makes sense. I did not realize the air all gets forced through like that.

Be aware, that's likely to generate a non-trivial amount of ozone. It may not be good for your health.

https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners

Thanks for pointing that out; I was unaware of that. After educating myself a little, it looks like UV light below about 200nm wavelength generate ozone, but 254nm is the sweet spot for killing microbes. The light I got works at the 254nm wavelength.

The US EPA recommends a concentration of less than 70ppb, Canada 40ppb, and the WHO 30ppb. This model has been tested by the California Air Resources Board at 13ppb.

That’s reassuring, but I’m still looking more into this. Do you have any recommended resources for gaining more insight on ozone generation?

https://www.environics.com/2025/02/17/regulations-ambient-ozone-concentration/

https://www.environics.com/2025/02/17/regulations-ambient-ozone-concentration/

https://bioshielduv.com/products/bioshield-magnetic

No, I don't, and I'm sorry, I just have looked into it before myself, and once I looked into it, decided I wanted to avoid it completely, So my research stopped there.

I do have a UV bulb that I've glued into a tote so that I can sterilize things like my CPAP. After that I will air it out for a very long period of time to make sure that all of that stuff is gotten out.

One thing that I can tell you that I've learned from what I've researched is that the more air that flows over the bulb, the more ozone will be generated. So if it's just sitting there not doing anything in still air and it's producing a certain amount, having it in your AC unit might produce more. So that might be an angle you might want to look into.

Practically speaking for an AC unit, what I think would be really useful is to be able to turn it on at the beginning of the season to kill whatever bacteria might be in there, or to just be able to periodically turn it on.

Huh, I hadn’t thought about turning the light on for short periods. And if ozone is mostly generated with moving air, then turning the light on with the furnace off seems to be safest. Thanks for the suggestion.

If your intent is to sterilize the coils so that they can't grow anything funky, then yes, probably that would be for the best.

Also, you could certainly test it by setting it to turn on when the furnace is on so you can see how stinky the ozone is. If it smells kind of strong, then that's probably too much, right?

"Mine" was a poor choice of words. I didn't install a UV light, but I did install an air Ionizer. My point wasn't clear: asking your HVAC tech for advice, since they service your system, I presume, and may have additional details like install pointers or potential impacts on warranties, etc.

Oh gotcha. Yeah I don’t really have an HVAC person to ask, but I found a few reputable sources on YT and they recommended on the underside of the coils, because that’s where the moisture (and then bacteria) accumulate.

I had it on for a few days straight and it didnt smell at all. But I think to be safe, I’m going to keep it unplugged and then run it for couple of hours each month (with the furnace turned off).