#1.8 Thermal Disinfection & Chemical Injection: What is the Right Mix for your System Update?

Legionella isn’t a “rare edge case” problem—it’s a predictable outcome of physics and biology. When water sits warm and stagnant, it becomes an incubator for bacteria that grows in the biofilm of the piping. In this episode, we step inside the lab to demystify Legionnaires’ disease and the plumbing conditions that allow it to thrive.

From the mechanics of aerosolization in showers and misters to the high-stakes environments of hospitals and hotels, we’re breaking down the "why" and "how" of waterborne pathogens. More importantly, we’re getting practical about the engineering and design strategies that actually mitigate risk.

What’s on the Menu:

• The Big Triggers: Understanding stagnation, dead legs, and the "danger zone" temperature ranges where Legionella is most aggressive.
• Design for Mitigation: How hot water recirculation and flow balancing prevent the "warm and still" conditions that lead to outbreaks.
• The Thermal Disinfection Strategy: Why programming a high-temp spike while the building sleeps is a powerful tool—and the hardware required to do it safely.
• Safety vs. Sterilization: The critical role of ASSE 1070 point-of-use mixing and ASSE 1017 master valves in protecting users from scalding during disinfection cycles.

If you work in plumbing, hydronics, facilities management, or healthcare design, this episode provides a clear, no-nonsense framework for reducing risk in both commercial and residential systems.

Transcript

Welcome From The Lab

Speaker 1 0:01

Welcome to the Ask Caleffi podcast coming at you live from the lab.

Speaker 2 0:06

Guys, what do we got going on? Plumbing, hydronics, expert insights, and a few stories from the trenches. Whether you're on the job or just along for the ride, we've got you covered.

Speaker 1 0:22

Hey there, welcome back to another episode of the Ask Caleffi Podcast. Here in the lab, we're to discuss some things. Uh Legionella, perhaps. Should we use that corny uh oh boy, corny sound effect every time we say Legionella? Yeah, it uh hangs around like fairy dust, doesn't it? It does.

Speaker 0:50

I've got a long episode of Legionella quite a few times.

Speaker 2 0:54

That kind of makes Legionella sound good. I know. Yeah, it's definitely not. We might scare you in this one. Yeah, we might.

Speaker 1:05

Oh wrong one.

Speaker 1 1:06

Hold on. Nope, not it either. Well, we're just gonna that's usually Dan's job is to press all the buttons on this thing.

Speaker 4 1:13

No, we're a minute into this and we got so many stupid sound effects.

Speaker 1 1:27

Uh it's gonna roll. Um, anyway. Legionella, you have, Matt, a pile of facts over there. It looks like uh Webster's dictionary puked all over in your lap.

Speaker 1:39

No, I I typed it nice and big so that I can see with my little old eyes.

Speaker 3 1:44

Well, share with us what you know, Matt.

Speaker 1:46

Yes, dude, do share.

Speaker 1 1:48

We know we know we know we have a solution to mitigate, right? We do. We do have a solution to mitigate, several solutions to help mitigate Legionella in systems. However, it's really not being chased that hard, is it, in the industry, unless it's a hospital or a place that's had known issues.

What Legionella Is And How It Spreads

Speaker 2:08

Yeah, yeah. No, that's so it is becoming more and more of an issue that's being kind of confronted, especially in, like you said, healthcare facilities, uh, nursing homes and hospitals, because a lot of the most at-risk people are elderly and weakened immune systems. And obviously, if you're in a hospital, you're not there for fun. Um, but really, what what is Legionella? So it's Legionnaire's disease is caused by this bacteria called Legionella. Um and it is basically in all water all the time. Um the thing is you can kill it. You can kill it with chemicals, with you know, bleach and chlorines and um and heat. And that's what is a really effective way to do so. I you can crank your water heater up to let me pull my shirt up here.

Speaker 1 3:05

You're gonna get into the good stuff, but the the crazy thing is is killing it with bleach or killing it with chemicals, what is that stuff doing to the piping? What is it? It's gotta go somewhere, right? So when you flush it, where's it going?

Speaker 3:18

Right. It's going right down the drain, obviously. And yeah, back into the water treatment facility eventually.

Speaker 1 3:25

And how much l time and effort goes into trying to treat that to get all that stuff out of there.

Speaker 3:30

I mean, you're it it's just an ongoing battle. There's always biologics.

Speaker 3 3:35

Yeah, so are are you really killing it or are you just managing it?

Speaker 2 3:38

Right. I think I think we're really mitigating and managing it instead of killing it and getting ready, getting rid of it. Yeah.

Speaker 3 3:45

Because it will start to regrow. It will. Yeah. I mean once your treatment is done.

Speaker 2 3:51

Right. And the perfect temperatures for it to grow are what between 80 and 120? 130? 110. Okay. Yeah.

Biofilm Stagnation And Dead Legs

Speaker 3:59

Like that's that's where it thrives, is between eighty and call 107, 110 Fahrenheit. Um and that temperate temperature and stagnation. Those are two real big factors.

Speaker 1 4:16

Uh those are two very big words. Yeah. Stagnation.

Speaker 4:21

Which, I mean, to that end, there's healthcare facilities um are starting to pick up on recirculating cold water, even at this point. That's that's one mitigating factor. I mean, just keep that water moving until it's down the drain, and you've got much less chance for Legionella bacteria to to grow. It really thrives in biofilm on the walls of pipe, which kind of acts as a food source. It does, yep. Yep, and a place for it to hide. Um and I mean, in every pipe that in every building there is biofilm. As long as it's been installed for you know more than a couple of months, you're you've got some sort of film on that pipe wall. It starts growing immediately. Exactly. Yeah.

Speaker 3 5:07

Especially in the right temperature range.

Speaker 5:10

Yeah. Yeah. So dead legs, again with the stagnation, um, that's become a real big issue too. Um, like we just had a code update, I know, here in the state of Wisconsin. I think it's now three pipe diameters. So, I mean, if you've got a two-inch main in a hospital, um, you can't have a dead leg on that longer than six inches.

Speaker 1 5:30

Wow. Okay. Yeah. And there's plenty of systems out there where we know for a fact that there's hundreds of feet of feet of dead leg in a building.

Speaker 5:40

Yeah. So moving forward, that's all, I mean, it's it's really gaining some traction and and uh well some attention.

Speaker 3 5:47

That's kind of where balancing is also going to be really important in your research system so that when you are in a thermal disinfection cycle, you're getting to all the all of the branches.

Speaker 1 5:57

Yeah, that's a good point. Right. Yeah. And we make a lot of different options that go into research systems, but we also have one in particular that works very well if set up correctly. In quotation marks.

Speaker 6:12

What's it called?

Speaker 1 6:13

Uh that would be the uh 116 thermosetter right there.

Speaker 6:18

Um I thought I was setting you up to talk about the Legio mix. Yeah, you know. Well, just a bit outside.

Speaker 3 6:26

Just a bit outside.

Speaker 1 6:27

I'm gonna channel my inner Harry Doyle right now.

Speaker 3 6:30

Yeah. So you you talked about using chemicals, Matt, but with with our Legio mix, we do thermal disinfection. You want to kind of just walk through a thermal disinfection cycle?

Speaker 6:40

Yeah, so that's um a real effective way um to disinfect an entire hot water system. Um, so what you can do is with our Legio mix valve that Greg is holding, um, it can be programmed however often you'd like, um, seven days a week, if you'd like, at certain durations. Um and what it you will so that this controller has uh a mixed outlet sensor that connects to it, and it's also got a recirculation sensor that connects to the hot inlet to the mixing valve. Um or I'm sorry, the recirculation line back in the mixing.

Speaker 1 7:17

The new controller will have one that tests to be continued.

Scald Risk And ASSE 1070 Valves

Speaker 7:22

Um but what it will do is, you know, say you set it up to um run 150 degree water, um, spike that for you know 45 minutes at two o'clock in the morning. And what that will do is that control will open full hot. It will give it, you know, as long as you're storing at 150 or above, it'll give it everything that it's got. Um, and that will be confirmed with a recirculation sensor. Hey, it's you know, run 150 degrees for half an hour, 45 minutes, whatever you say. And then it will go right back to normal mixing. Now, one thing that is absolutely critical if you are running a Legion L disinfection program in any building, you need to have ASSE 1070 point of use mixing valves at every fixture served by that.

Speaker 1 8:10

You aren't gonna make me reenact my engineer voice. Well, what if we don't have that in there? Don't even program it. Don't even think about it. Don't touch it.

Speaker 8:20

Yeah, I mean, it's just the liability of yeah, some little sweet little old lady goes to wash her hands at two o'clock in the morning and that 150 degree water comes out, it it takes a fraction of a second.

Speaker 3 8:31

Okay. So that'll ramp the water temperature up on and register that it hits that design temperature on the mixed outlet and then confirm it with the return with the research sensor.

Speaker 8:42

Exactly.

Speaker 1 8:42

Yep. I almost feel like we should break out the whiteboard and the colored markers and like draw a drawing out for uh everybody to see how this works because we're all visual learners. But uh to kind of recap what a system should look like, we're gonna start off in the mechanical room, right? Water heater, water, hot water plant, maybe it's a bank of tanks with an indirect or whatever that looks like, but you have your your source, and say we want to control Legionella, we're gonna set that source to the the temperature we want to control Legionella at, right? So maybe it's 150 or maybe it's 140. So your source temp is 140. You're gonna send it to an ASSC 1017 mixing valve, like the Legio mix right here. This one's electronic 1017 valve, and then we're gonna run a research system throughout the building. So a research return. So every one of your uh we'll say water delivery zones. Does that make sense? Yeah, branches are branches, every one of your branches is gonna come back to a common return, and each one of those delivery areas is going to have anti-scald in it. So an ASSC 1070 valve under every lavatory, uh showers. Showers are kind of a gray area to me. I mean, do most of them have skull protection built in. So they're already what what would they be? A 1069 or 1071? You caught me off guard, but got you good.

Speaker 10:23

I think it's a 71. I think 1069 is the emergency figure. Yeah, I think it is. I think that's eye wash.

Speaker 1 10:28

That's eye wash. So I forgot to study my ASSC 10 uh ASSE booklet here. Uh and I I forgot to slide you a copy for later.

Speaker 3 10:37

But the test is until this afternoon. Okay, okay. We got time.

Speaker 1 10:40

We got time. Um, but yeah, so anti-skull that each any place that water is going to come out. So whether it's a hand wash sink, a shower, tub, that kind of thing, you got to have anti-skull there.

Recirculation Design And Balancing Basics

Speaker 10:52

Any place that that that hot water is coming from that mixing valve, any fixture that that's touching has to have some sort of skull protection built in or installed.

Speaker 1 11:02

Where that gets a little gray and changes is when we're talking sanitary, like kitchen and laundry. That that's usually high temp all the way. You're not controlling anything there. True.

Speaker 3 11:13

Yeah, but that's usually piped back directly and not through that mixing valve. Hopefully.

Speaker 1 11:17

So that hopefully should be. Um that's the goal. So we're delivering to Anna Scald. Now we gotta come back, and each each area needs each riser, it needs a riser to come back to that main return line where the research properly sized research bump in a perfect world, which we know the round the world is round, it's not flat, right? So nothing's nothing's perfect. Um, for all you flat earthers out there. It uh it needs to be balanced, each one of those risers, because we all know water is lazy, it takes the path least resistance. So everything that is close to the mechanical room is probably gonna be okay for hot water delivery. We're gonna have you know, flip on a faucet, it'll be right there. Hotels are notorious for this, and I think hospitals are probably almost as bad in some cases because it's like a big hotel for sick people, right? Pretty much. So it's uh hotels sucks. Hotels sucks. Yeah. Um it uh you have different resistances, you're gonna have a lot of losses in them systems. So you need to be able to create a pressure drop in there to help divert that water on, and that's what a balancing valve is. Exactly. It just it's a pressure drop, you're creating a small pressure drop just enough to allow that water to push on.

Speaker 3 12:43

Exactly.

Speaker 12:44

Yeah, a little something in that pathway to send that that pressure down the line. Yeah.

Speaker 1 12:51

But anyway, that's in a nutshell, that's kind of where how that system's working. You have your return coming back, going to the cold inlet side of the mixing valve, and back to your your plant, whether it's a bank of tanks or a single tank, whatever that looks like, to be able to uh allow that water a place to go every to every everywhere it needs to. You know, when the valve goes to close close cold, that water flow still needs to continue, so it's gonna go back to the tank when it opens more to hot, then it'll allow it back through the valve again.

116 Thermal Setter Options Explained

Speaker 13:24

Exactly. Yep. I kind of cut you off earlier, but yeah, what's unique about that 116 as far as Ryan? Why don't you take that one? There's your test.

Speaker 5 13:36

What's so unique? What's so cool about this one? You've been kind of quiet, right?

Speaker 1 13:39

I have you've got to be. We're putting you on the front line.

Speaker 2 13:45

So our 116s thermal setter. So that is adjusting the flow by the temperature.

Speaker 1 13:50

Yeah, not a not a number, right? Not a number, not a flow number, not a GPM number.

Speaker 2 13:55

Right, right. So we have four different kinds of thermal setters. We got your basic one, which is our 116s, and those are where you set the thermos the temperature, and it'll balance off of that.

Speaker 1 14:07

Yeah, that's the 1164, and all it has in it is just the temperature cursor.

Speaker 2 14:13

Yep. Um, and then we have the 1162, which has our bypass for 160 degrees, and then we got the 1166, which is the 140 degree temperature, and then we have the 1162, which is just like this one here, where it has the well for a cartridge to slide in, or even an electric actuator.

Speaker 1 14:38

Yeah, we call that baby the Swiss Army knife, at least I did, you know, it because it's it's Legionella ready. Yep. So if you have a job where it may or may not require it, you kind of want to cover your butt and not have to go back and change a valve. Because the lay length between the 1164 and the 1161, 1162s, uh those it's gonna be a little bit different. You gotta essentially another inch of space there that you need to be able to put that second cartridge, that disinfection cartridge in.

Speaker 2 15:07

Right, right. Yeah. So yeah, when you're setting these guys up, you set them. So let's say you have 120 coming out of your Legio mix, and you set these 10 degrees less. And when it hits that 110, it'll start shutting down. It doesn't shut down fully, but it'll start to shut down and then build that pressure up and have it basically balance the system by itself.

Speaker 1 15:30

Yeah, yeah. It's a very smart balancing system. So, Dan, I'm gonna put you on the spot. There we go. Yeah, how does the disinfection cartridge work in those? If we know we've got 140 degree water coming to this, we'll say, and then all of a sudden, well, we're set to 110. That that balancing cartridge is going to drive closed, right?

Symptoms Plus Time Temperature Kill Rates

Speaker 3 15:50

Yeah. So as as you elevate that source water temperature out to the system, it's gonna start to see that elevate up above. You know, if that valve is set to 110, it's gonna see it hit 110, it's gonna modulate down to its lowest point of closure. Once that temperature elevates and hits the 140 degree mark, that bypass cartridge is gonna pop open and allow that flow back to bypass your thermostatic cartridge and then disinfect that circuit. As that temperature starts to come back down, once it drops below the 140, that cartridge will close and they'll go back to the temperature mixing or temperature balancing. Sorry.

Speaker 1 16:27

I couldn't have said it better than myself. I mean you did great. You did a great job.

Speaker 3 16:32

See, apparently we're all ready for the test this afternoon. Yeah, right.

Speaker 2 16:36

Greg needs a little bit more studying.

Speaker 1 16:40

Matt, you have a pile more facts there. What else can you share with us?

Speaker 16:45

Um do well, I'm I mean, I've just got the kind of the nitty-gritty um about what Legionella is and everything like that. But um basically, I mean it's it you'll feel nauseous, fevery, headaches, um, coughing. It's it's a pneumonia that's caused by inhaling Legionella bacteria. So aerosolized, so in a in a shower. That's not, you know, say say your water here is only set to about 110 and rarely used. Um you know, that that can actually be breeding a lot of bacteria. Then you go to take a shower, you've got all that aerosolization, um, and you inhale that, that's where where that comes from. Which again in in healthcare facilities, I've heard they are kind of banning um even at at faucets, aerators, and want all laminar flow fixtures now, um, which obviously will help reduce a lot of that.

Speaker 3 17:45

Um, you think in a normal residence, you probably get enough use of your hot water system that you know you're gonna flush and it's gonna be safe. But you're right, you get into a hospital or a hotel, depending on occupancy, um, there might be a bank of rooms that don't see a lot of use and potentially sit in that growth range.

Speaker 18:05

Right. I mean, if you've got a wing that you know is only 20% full, you know, and barely anybody, you know, is using the the water, that gives plenty of time for stuff to to grow. Um here's uh little fact that this is in a lot of our literature too, that's where I stole this little graphic from, but um at 160 degrees, the bacteria is killed instantly. At 140, 90% of the bacteria is killed in two minutes, and at 120 degrees, 90% of the bacteria is killed in two hours. So you can see there's quite the rapid um succession of of how quickly that can get eliminated the higher the temperature goes. Which is why we make not just our Legion mix, but in like a residential setting, um, our tank mixer is a really good feature. You can crank your tank up, store it at 140. You know, all pretty much everything in there is any legionella that's in there is gonna be dead, and you're going to get some increased capacity basically from your heater.

Speaker 3 19:09

Yeah, you're storing in the safe zone.

Speaker 1 19:11

Exactly. Yeah, that's that's really what it's about. Adding capacity and keeping things sanitary as sanitary as you can.

Speaker 19:21

Exactly. Cool.

Speaker 1 19:23

And that's all information that's you know, basically it's off the CDC website, really.

Speaker 19:29

Pretty much, yeah. I mean, it's it's again kind of pretty much everything that I've um got into already about you know, weaken immune systems, elderly um are are kind of the more susceptible to something like this. But yeah um just in in general, I mean it should go without saying, but it's it's good practice to store at or above 130, I would say at least. Um and then and then mix down. You shouldn't have anything to worry about.

Aerosols From Showers Fountains Misters

Speaker 2 20:02

So don't open your mouth when you're in the shower. Yeah, don't do not breathe in the shower. Do not drink our water. I'm gonna wear my mask in next day. Yeah, makes you think. It does. It does. It does.

Speaker 1 20:15

Well, even you know, summertime. We're here, we're coming into summertime. There's gonna be restaurants and places with misters, right? Yeah, misters or fountains. Fountains, I mean it can be found in there, even, which is kind of a weird thing, but to to even have to consider worrying about it.

Speaker 3 20:30

But it's think of a mister or um a fountain, you're taking that water and aerating it, throwing it in to be breathed in by the people around it.

Speaker 20:39

So I believe the very first major outbreak was due to a fountain, actually.

Speaker 3 20:45

Oh, yeah.

Speaker 20:46

Um, yeah, and those are kind of falling by the wayside as far as designs go.

Speaker 2 20:54

Right. It's just something that you never thought of. Yeah, right. Personally, something that I had never even thought of. No, we took it for granted.

Speaker 3 21:01

Yeah, right. Nope. I know anytime I'm traveling and in a hotel or you know, you go somewhere warm with all the fountains, it's like it's kind of a breeding ground here.

Questions Subscription And Closing

Speaker 1 21:12

Not only for that, but other things. Yeah, right. Stuff we don't offer control over. Well, uh, I think we covered Legion L and kind of how to control it with what we have. Uh, if anybody has any questions, don't hesitate to uh give us a call and talk to us about it. Brian loves to chat. You love it. Love it. And uh Matt will just sit there and nod. Absolutely. We've got you covered. A special tip. All right. Well, everybody, thanks for listening. See you in the next one. Thanks, everybody else.

Speaker 2 21:47

Well, that's a wrap for this episode. Got questions or stories to share? We'd love to hear from you. Reach out and let's keep this conversation going. Don't forget to subscribe and leave a review wherever you listen.

Speaker 1 21:57

Until next time, stay curious and keep the Your systems running smoothly.