UV-C Germicidal Furnace "Filter"
Having suffered from allergies most of my life, anything that promises to "help with allergens" tends to be of great interest.
Premise
Ultraviolet "C" band light is well known to be toxic to almost any living organism, from viruses to people. (See stupidity here: https://www.nytimes.com/2023/11/07/style/bored-ape-nft-eye-burn.html )
I want to use this same "Kill EVERYTHING" approach to any living contaminants that may have found their way into my central HVAC system. UV-C is already used for this exact purpose in commercial products and systems, but the pricing can be exorbitant for an off the shelf unit. My price comparisons went from ~$500 for what I considered an under-powered unit up to ~$5000 for a cool fluorescent system that MUST be installed by approved HVAC tech to have any warranty.
Design
This only qualifies as a design in the strictest sense, since even a table lamp has a switch!
- 2x - 50W+ E27 size UV-C COB LED bulbs
- 2x - Ceramic un-switched E27 light outlets
- 2x - 1" deep electrical light boxes
- 6' - 18/2 home wire (18ga with black, white, ground)
- 4' - 1/2" weather stripping
- Right Angle 3/4" clamping box fitting
- 24"x12" 22ga steel sheet
Build
We begin by looking at the furnace system we want to modify; can we find a place about 6-8 by 10-16 inches? it is recommend to go with a standard "off the shelf" vent size such as 8x16", which would enable easy retrofitting if the home is sold etc.
Once we have the location and size chosen, cut and smooth the edges of our sheet metal plate to match a 1" overlap on all sides so our plate overhangs the hole we will cut in the HVAC system. I used some 3mm screws with nuts to mount the electrical boxes onto the sheet metal plate. I used some PETG-V0 Flame Retardant filament to 3D print the electrical boxes, to ensure I added a little fire load to the furnace as possible!
Both light fixtures are connected in parallel with the grounds each being terminated to the metal sheet inside each box for extra safety.
Notes
Wiring was harder for me than it should have been since I used "scrap" materials wherever possible, this left me wiring 130W of total power lighting with 12ga heavy wire instead of the 18ga or similar that could also have been used.
I ended up going the LAZY way and wired these in as "on all the time", since my HVAC system blower motor is Variable Frequency Drive meaning there is no convenient place to hook up the lights to a switched 120VAC output like I hoped.