HVAC UV lights

Sac Arrow

Sac Arrow

Touchdown! Greaser!
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Snorting his way across the USA
So, there I was...

Staring at the new HVAC installation. Pretty slick. They did a bang up job, and other than a minor issue with the thermostat (fixed 1 degree differential temperature setting) I really like it. All options included either a UV light or an ozone generator. I guess it was an ozone generator but I opted for the base system with the UV light.

I did a bit of research. After the fact. They light up the coil, and kill pathogens that might reside in the condensate during AC operations. Fine. Great idea. I'm on board with that. But, the system, as installed, has the UV light going 24/7 all year long. I get that during AC operation, you might want to have the light on as long as there is liquid condensate on the coils. But, during the heating season, it would (I assume) be completely useless and a waste of bulb life and energy.

So, there I was...

Staring at some SPST flush mount switch options on the Zon. I already ordered it, so it's on the way. It's easy enough to wire in a switch to the DC connection to the light from the power supply. 3 amps should (I hope) be more than adequate.

Question:

Am I missing something? Is there another reason to keep this light on continuously? In fact, is there any reason to keep this light on at all? Because I suspect when the bulb burns out, I probably won't replace it. I know, why did I buy the switch.
 
I’ve never let them install one in any of my ac’s because I think it doesn’t do squat. The bad stuff isn’t there long enough for UV to hurt it IMO.

But I would think you’d leave it on 24/7 especially when the heaters running. Most stuff that’s going to hurt you thrives at 98.6 degrees.
 
Salty said:
I’ve never let them install one in any of my ac’s because I think it doesn’t do squat. The bad stuff isn’t there long enough for UV to hurt it IMO.

But I would think you’d leave it on 24/7 especially when the heaters running. Most stuff that’s going to hurt you thrives at 98.6 degrees.
Click to expand...

Good point. But, there would be basically no moisture. So...
 
And by the way I suspect it doesn't do squat either.
 
Mine runs 24/7….. how many watts is it drawing? Wonder how much in-rush current you’ll see flicking it on and off? Mine is only 9 watts….so it’s cheap even if it does nothing. Lol
 
Salty said:
I’ve never let them install one in any of my ac’s because I think it doesn’t do squat. The bad stuff isn’t there long enough for UV to hurt it IMO.

But I would think you’d leave it on 24/7 especially when the heaters running. Most stuff that’s going to hurt you thrives at 98.6 degrees.
Click to expand...
I suppose it may depend on the installation and the organisms. This article claims effectiveness against molds:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC93076/
 
We got a new HVAC unit in year before last. The company came in after 12 months for their final "1 year post-installation check-up". The guy that came said "Everything looks fine, but I'm supposed to suggest that you buy this UV light to attach to it as well." I said "Does it really do anything?" He said "Not really. Will you sign here acknowledging that I suggested it?" I said "Sure."
 
GeorgeC said:
Invisible light killing invisible organisms? Sounds like a hoax.
Click to expand...
The theory is valid, the argument is whether the application is actually capable. UV is used in aquaria with great success to control pathogens. But it's very important that the dwell time of the water going through the UV is long enough to be effective.
 
Sac Arrow said:
So, there I was...

Staring at the new HVAC installation. Pretty slick. They did a bang up job, and other than a minor issue with the thermostat (fixed 1 degree differential temperature setting) I really like it. All options included either a UV light or an ozone generator. I guess it was an ozone generator but I opted for the base system with the UV light.

I did a bit of research. After the fact. They light up the coil, and kill pathogens that might reside in the condensate during AC operations. Fine. Great idea. I'm on board with that. But, the system, as installed, has the UV light going 24/7 all year long. I get that during AC operation, you might want to have the light on as long as there is liquid condensate on the coils. But, during the heating season, it would (I assume) be completely useless and a waste of bulb life and energy.

So, there I was...

Staring at some SPST flush mount switch options on the Zon. I already ordered it, so it's on the way. It's easy enough to wire in a switch to the DC connection to the light from the power supply. 3 amps should (I hope) be more than adequate.

Question:

Am I missing something? Is there another reason to keep this light on continuously? In fact, is there any reason to keep this light on at all? Because I suspect when the bulb burns out, I probably won't replace it. I know, why did I buy the switch.
Click to expand...
Off topic a little.
20 years ago one of our LP gas fuel customers was complaining about black stuff in their house. We could find nothing wrong with the LP gas pressure regulators that would cause the furnace to run dirty. The HVAC company was there many times trying find the problem. They installed a UV light in the duct work to try to solve the problem. It did not work.

Then the whole house burnt down! Turned out the flue pipe was too close to some wood framing that no one could see and it eventually caught fire.
 
Gary Ward said:
Off topic a little.
20 years ago one of our LP gas fuel customers was complaining about black stuff in their house. We could find nothing wrong with the LP gas pressure regulators that would cause the furnace to run dirty. The HVAC company was there many times trying find the problem. They installed a UV light in the duct work to try to solve the problem. It did not work.

Then the whole house burnt down! Turned out the flue pipe was too close to some wood framing that no one could see and it eventually caught fire.
Click to expand...
Funny now I'm "defending" UV, but in fairness, even if UV did work, adding it afterward is not going to resolve a mold problem in the ducts. In theory it could prevent it from starting, by killing the pathogens before they went into the duct. But once, there, the UV won't be able to help.
 
Salty said:
Funny now I'm "defending" UV, but in fairness, even if UV did work, adding it afterward is not going to resolve a mold problem in the ducts. In theory it could prevent it from starting, by killing the pathogens before they went into the duct. But once, there, the UV won't be able to help.
Click to expand...
I am not saying IMO that UV light does not work. I am saying that was the first time I've heard of UV filtration. It didn't work in this case because the impurity's was not in the duct work.
 
Just to be clear, I am familiar with UV in municipal drinking water disinfection and reclaimed water disinfection. The reactors have to be very carefully designed so that the pathogens present in the water get a uniform, lethal dose of UV light. Which is why a single stick of UV bulb in a condenser plenum isn't likely to do much. Whatever pathogens happen to flow by the bulb will get zapped but that's about it.

I may just disconnect it altogether. I'm not installing the switch until the inspections have been made, in case they don't like something about my wiring job.
 
Checkout_my_Six said:
Mine runs 24/7….. how many watts is it drawing? Wonder how much in-rush current you’ll see flicking it on and off? Mine is only 9 watts….so it’s cheap even if it does nothing. Lol
Click to expand...

I don't know off hand. The power supply runs hot to the touch so it is drawing enough power to significantly affect my bill. Inrush current? It's a light, not a motor, and I'm not going to be flicking it on and off. I might run it when the AC is active. Or not. Haha.
 
Are people getting sick in their homes and I missed it?
Sounds like a solution looking for a problem.
 
Salty said:
Funny now I'm "defending" UV, but in fairness, even if UV did work, adding it afterward is not going to resolve a mold problem in the ducts. In theory it could prevent it from starting, by killing the pathogens before they went into the duct. But once, there, the UV won't be able to help.
Click to expand...
The post you replied to didn't mention mold.
Salty said:
The theory is valid, the argument is whether the application is actually capable. UV is used in aquaria with great success to control pathogens. But it's very important that the dwell time of the water going through the UV is long enough to be effective.
Click to expand...
See this reply:
Cap'n Jack said:
I suppose it may depend on the installation and the organisms. This article claims effectiveness against molds:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC93076/
Click to expand...
 
Let'sgoflying! said:
Are people getting sick in their homes and I missed it?
Sounds like a solution looking for a problem.
Click to expand...
I've had mold in my home that went undiscovered long enough to cause health problems.
 
Checkout_my_Six said:
well then....why bother with filters?
Click to expand...
I have had my ducts cleaned twice over the years. The first time was eye opening all the junk they got out, like drywall from when they built the house.

Then when I had a new furnace installed. I removed the old furnace ahead of time with the blessing of the installer. I painted the concrete floor where the new furnace was going, but more important I pressured washed out the steel ducts in the basement, return and fresh ducts. That made me feel good. Let it sit for few days to dry out.
 
Gary Ward said:
Then when I had a new furnace installed. I removed the old furnace ahead of time with the blessing of the installer. I painted the concrete floor where the new furnace was going, but more important I pressured washed out the steel ducts in the basement, return and fresh ducts. That made me feel good. Let it sit for few days to dry out.
Click to expand...

What did you find when you pressure-washed the ducts after the original cleaning?
 
UV lights work and are installed in new hospital air handling systems for this reason. They oxidize biological material including bacteria, mold spores and similar. This biological material is not limited to the condensate on cooling coils. Mold spores are airborne as are many other types of bacteria. The science is solid , but the world seems to be full of science deniers so people will believe what ever they choose.
 
Lndwarrior said:
UV lights work and are installed in new hospital air handling systems for this reason. They oxidize biological material including bacteria, mold spores and similar. This biological material is not limited to the condensate on cooling coils. Mold spores are airborne as are many other types of bacteria. The science is solid , but the world seems to be full of science deniers so people will believe what ever they choose.
Click to expand...

Where do I start on this.

Okay. Yes, they work. Again, I will say that in order to effectively use this method of pathogenic destruction, the environment has to be carefully designed to allow it to work.

I suspect that is the case with your hospital air handler system. I do not believe that is the case with my (our) typical residential system. But to simply throw "science" in there, as a catch all, which seems to be the trend lately, well, that seems weak.

Not hating on you bro. Just venting on something that bugs me.
 
Here’s my two cents as I’ve been in the biz for 25 years, so I’ve seen a thing or two….

The biggest problem usually revolves around the drain line. When it gets plugged, and the water backs up, the mold starts to grow and is constantly fed. I’ve seen entire units turn into mold factories and they’ll go unnoticed for years.

The first line of defense should be a good drain monitor such as a screw in float switch or an in-line drain monitor. Throw in regular maintenance of the drain line at the start of every summer before you flip on the air. You can do this as a customer. This alone will prevent probably 99% of the bad I see.

Again, my two cents.

Bob
 
I know it works. Since I installed my uv light I only got COVID once. ;)
Lndwarrior said:
UV lights work and are installed in new hospital air handling systems for this reason. They oxidize biological material including bacteria, mold spores and similar. This biological material is not limited to the condensate on cooling coils. Mold spores are airborne as are many other types of bacteria. The science is solid , but the world seems to be full of science deniers so people will believe what ever they choose.
Click to expand...
 
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