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I want to install a UV light inside my home HVAC duct. These UV units come as self-install kits: just drill a few holes in the duct and attach the unit to the sheet metal wall of the duct with a few self tapping screws. That sounds easy.

But two of the holes are 1.75" in diameter. Drilling those holes will result in metal fragments. (The instructions say to drill holes.)

I was planning on putting the UV units in the output plenum above my Trane HVAC.

Should I be concerned about the possibility of metal fragments dropping down into the bowels of the Trane unit? If so, what should I do to avoid the fragments?

Should I put the UV light in a return plenum, to the side of the Trane unit, right before the air filter or just not worry about the metal fragments.

(I prefer to put the UV above the Trane because it is closer to the 110v outlet.)

Or is there another way to make the hole without leaving metal fragments in the duct?

Added: Return plenum on the left. Output plenum above the main unit, in the center of the photo. enter image description here

Update: Based on the input from this forum I decided to put the UV light unit in the return plenum for two reasons: (a) if any little pieces of metal happen to fall into the duct, they will not get into the fan, (b) there are no plastic parts in the return duct, so there is no risk of the UV light causing deterioration of the plastic over time. I also decided to cut the hole w tin snips.

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  • disconnect the duct
    – Traveler
    Dec 15, 2022 at 4:21
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    a picture of your setup and the proposed location of the holes would help. Dec 15, 2022 at 6:15
  • Too broad. Worrying about swarf in the system is a totally different question than where to locate the unit in the first place. Please edit to ask one question, then ask the other question as a totally separate question. You've got a nice answer to one part of the question already, so make this about swarf, then make the new question about where to mount the unit in the first place. Otherwise, you'll invalidate the good answer you've got.
    – FreeMan
    Dec 15, 2022 at 13:42
  • Holes in sheet metal are usually cut, not drilled. If you happen to be using woodworking tools, just vacuum up after. No biggie.
    – isherwood
    Dec 15, 2022 at 13:44
  • @isherwood (1) How do I cut a hole in the side of the duct without drilling an opening? (2) The installation instructions show drilling a hole in the duct.
    – Yehuda_NYC
    Dec 15, 2022 at 13:59

3 Answers 3

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Should I be concerned about the possibility of metal fragments dropping down into the bowels of the Trane unit?

It would concern me, yes. It's a direct drop into your blower. If a fragment gets caught then you could have an awful scratching noise when the blower activates.

Realistically, nothing is likely to happen. An HVAC tech wouldn't even think once about this problem.

How to avoid metal fragments inside HVAC duct?

Use tin snips. Pick left or right cut snips based on which direction you'll be cutting the circle. To start the hole so you can get the snips in, use a chisel or an old-fashioned can opener. Video demonstrating screwdriver method: https://youtu.be/iqgqmmVcatQ?t=98

If you prefer a perfectly circular hole then disconnect the plenum from the A/C coil, lift the plenum, slide some cardboard or plastic sheet inside, drill the hole, lift the plenum again, and remove your cardboard or plastic sheet. See picture below:

You could use a diamond hole saw to eliminate the metal fragments issue and hold a vacuum nozzle while you're drilling to mitigate 95% of the dust.

enter image description here

Should I put the UV light in a return plenum, to the side of the Trane unit, right before the air filter or just not worry about the metal fragments.

The UV light needs to shine down on top of the A/C coil. The instructions should explain this.

UV light wreaks havoc on most plastics and air filters.

UV doesn't purify air, it prevents growth on surfaces; particularly, your A/C coils.

(I prefer to put the UV above the Trane because it is closer to the 110v outlet.)

Your opinion doesn't matter, follow the instructions. Also, most UV lights are 24 volts so you'll need to wire in a small transformer.

Below is an excerpt from a Honeywell UV2400U5000 which I've installed.

We recommend the UV Air Purifier be installed on the supply side duct 3–5 inches above the A-coil, but it can also be installed on the return side if necessary. See Figures 1 and 2.

The germicidal UV light should be positioned to shine on the surfaces that are prone to mold growth like the A-coil, or be placed in an open area of the return duct where there are long straight runs.

Source

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    Comments are not for extended discussion; this conversation has been moved to chat.
    – BMitch
    Dec 19, 2022 at 14:53
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yeah metal fragments are bad in there, if the got on the aluminium evaporator coil they will cause galvanic corrosion, id the land in a galvnised drip pan that will also cause galvanic corrosion. but it's a slower process.

punch a hole with a sharp piercing tool like a drywall screw or bradawl, tear it large enough to get offset snips in there and then cut the circle. being careful not to drop any pieces inside.

practice on some empty tin cans first

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If you are drilling up into the metal I'd expect the majority of any metal to fall down and out of the hole as you drill. After drilling the 1.75" hole put a shop vac up to the hole that will suck any loose bits of metal that are inside of duct.

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  • I am concerned about even a minority of the metal pieces inside the duct near the HVAC unit.
    – Yehuda_NYC
    Dec 15, 2022 at 14:47
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    Shop vac will take care of the minority. Dec 16, 2022 at 2:14

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