UV Light

Nan's Nook : Archives : Grow Chambers & Clean RoomsHow to make a "clean room" : UV Light
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HEPA Filters  -    

By relic (Relic) on Wednesday, December 05, 2001 - 01:31 am:

heard of these? i'm going to install one on my furnace/ac. it installs on the return duct and kills 100% of germs, fungi, viruses, etc. in the air*. it is on 24/7 whether the furnace/ac is on or not. so it is still working on the passive air flow through the duct system and uses about 30 watts of power. the bulb has to be replaced once a year or so. it should improve the overall air quality in the house by leaps and bounds.

* Blacklights are UV lights - Nan

By jim brown (Shrhobbyist) on Wednesday, December 05, 2001 - 01:38 am:

I've heard of a UV light, of course, but never for such a use as this. Can you expand a little? How is it attached, where does it go on the furnace? Where did you get this idea? Anyways, thanks for the lead, Relic.

By relic (Relic) on Wednesday, December 05, 2001 - 02:20 am:

typically it installs in the return duct before it enters the furnace. if you have an upflow furnace it would be installed high in the return air drop duct that connects to the side of the unit. if you have a downflow, it installs in the plenum above the furnace, which can cause problems b/c that is directly above the blower compartment which has wiring in it. if there is a single connecting r/a duct connecting to the r/a plenum, that would be the place to put it. it needs to be in a sealed duct so no light can escape as UV light is very dangerous to the eyes. it also can't be in a duct that has any wiring in it, as it will destroy the wiring. it also may have adverse effects on "flexible" ducting if it is installed where the light will enter any flex duct.

my father-in-law is in the hvac/r biz and he turned me on to it. they are sized based on square footage x ceiling height(cubic feet of air in the house) of house and come in like 3 sizes for residential apps. a 12", 18", and 24" bulb legnths. there are types that have air sensing switches that are only activated when the furnace is running. the kind that is on all the time is preferable from what i hear.

they are really easy to install, you have to have a forced air heating/cooling system(not mobile home). basically you put the proper hole in the r/a plenum, attach it, and plug it in. the bulb on the good ones will go at an angle so there is no 'dead spot' at the end of the bulb that doesn't get the UV light in the duct. at an angle the light is cast across the duct completely.

the wholesale cost for an 18" is like $170 and shouldn't take more than an hour to install, so don't get ripped off if you choose to have a pro install it(not a bad idea). probably not a bad idea to have your ducts professionally cleaned as well, if needed. while it may stir up more contams and dust in the short term, in the long run it's better for your air quality. and don't use those cheap-ass blue filters, get one of those $3.50-$5 pleated types if your using a 1" filter, and change it at least every 3 months. or get one of those 3" pleated filters installed if you're really into it.

By SYDYSTYK (Addict) on Wednesday, December 05, 2001 - 03:03 am:

in bob harris' book he says that uv doesnt affect fungus

By plinkerdink420 (Plinkerdink420) on Wednesday, December 05, 2001 - 03:55 am:

wow relic... thanks for the cool info.. i'll have to keep that in mind if i can ever get outta the renter's game and into my own home

By relic (Relic) on Wednesday, December 05, 2001 - 06:09 am:

it is supposed to kill mold, bacteria, yeast, dust mites, and viruses. it doesn't kill all of the 'things' in the air on a single pass. but it should greatly reduce them. i guess you can install it on either the supply or the return and for the best effectiveness you should use 2 bulbs criss-crossed at opposite angles. here's a picture of a page in a technical manual.


By SYDYSTYK (Addict) on Wednesday, December 05, 2001 - 06:54 am:

ok im going to quote it for information sake probably should get a few opinions from the experts (though bacteria alone would be a good reason to rotate one of these light between your chambers)

From "Growing Wild Mushrooms", by Bob Harris

"For myself, I add a germicidal UV (ultraviolet) fluorescent lamp, but i think you can acheive good results without this. The UV lamp only works on bacteria, not fungi. (The DNA structure in bacteria is sensitive to UV light and is destroyed by it while fungi are not.) "

he has on in his glove box which he then uses for streaking and such, i couldnt see him using it if it kill fungus spores

By George W. Bush (Xatomichristx) on Wednesday, December 05, 2001 - 07:09 am:

hmmm...well, just my two cents, but for me, bacteria contams aren't my problem, mold is, and i don't think that high intensity UV will kill just mold and not fungus, i would think it would kill both, or neither....also, remember : They aren't talking about black lights, all that putting those up will do is impress your tripping friends when you show them the "rubbermaid of happiness"

By Imok Urok2 (Imok) on Wednesday, December 05, 2001 - 07:23 am:

Well, even if it just kills the mold, bacteria, yeast, dust mites,
and viruses in your living space it would be worth it.
My wife has severe sinus infections on a constant basis.
We had our ducts cleaned and that helped some.
Our house already has one of those expensive ($65)
pleated filters,
on the intake duct, that are not available in the store but only from
a "professional" (sounds like what they would say about this equipment too).
This UV bulb in the duct might do the trick.
Thanks relic

By relic (Relic) on Wednesday, December 05, 2001 - 07:41 am:

it is highly unlikely that he would put the type of bulb i'm talking about where he could see the light, this would be dangerous. i read somewhere that spore are harder for the UV to kill, but that UV can kill them. duration and intensity probably have a large effect on the results.

i just found a link to the product i will be installing, there are links at the bottom of the page regarding UV intensities required to kill different molds.


the criss-cross installation shown in the previous post looks like the best way to go. even if it is somewhat ineffective against mold it will make the air cleaner. maybe help keep from getting colds and such too.

By ion ewe (Ion) on Wednesday, December 05, 2001 - 11:46 pm:

Also, you must all remember that this only kills things; you must still filter the dead bodies out of the air. Hey, Relic, can you install these things near the filter? I would think it more effective for the mild air turbulence and slowing at such a point.

SYD, you must remember that spores are usually quite hard and impenetrable. Their protein sheaths are, however, vulnerable to radiation. This process simply renders them sterile.
I believe what your book is referring to is streaking with whole tissue. The tissue of a fungus is far less susceptable to death by UV, as the sun is our most potent natural source of such. Uncovered spores left in the sun will "die" within the day, but only the weakest will "die" in the short time it would take to transfer some to petri dishes. This is a good thing when cultivating a species.


By SYDYSTYK (Addict) on Thursday, December 06, 2001 - 12:00 am:

uhhh he used it for spore streaking but he reccomends 15-25 watt, dont get me wrong this is a bad ass idea and i would like to know the results, however i was curious why you just dont use a HEPA?

By relic (Relic) on Thursday, December 06, 2001 - 05:22 am:

you can install one near the filter, they say it is better after the filter b/c the bulb will stay cleaner. but, the bulb can be removed from time to time and cleaned.

syd, that's not a bad idea either. i've never seen a hepa air filter system for a residential heating system. i'm sure one could build a rack for it. you would definately want a good prefilter.

By Imok Urok2 (Imok) on Thursday, December 06, 2001 - 07:39 am:

Maybe a dual filter cartridge?