Legionnaires Disease An Issue With Reverse Indirects?

D107 · May 2019

I'd like to verify what I've been told that Legionnaire's bacteria is not an issue with a reverse-indirect like Turbomax. This is supposedly because the domestic water is only within a coil that holds only a gallon or so. I have adjusted the Turbomax's aquastat to cut-out at 150 and cut-in at 135. The aquastat probe is positioned more than halfway down the tank, which likely means when it cuts out at 150, the water temp at the top of the tank could be 160. So assuming the aquastat is calibrated correctly--not a certitude by any means--the tank water fluctuates between 135 and 150 where the probe is, and a bit higher at top of the tank, and transfers X% of that heat to the actual DHW inside the coil. Perhaps the Turbomax engineers put the probe so low in the tank to simulate the actual temp of the water inside the dhw coil.

In order to cut down on the number of DHW calls during the day when there is little or no hot water usage, I'd like to lower the cut-in temp 5-10 degrees. (as long as this wider cut in-cutout spread, like a heating temp setback--does not waste more gas than it saves trying to make up the differential.)

As it is, tank water temp drops enough to force boiler to fire every 5 hours or so for about ten minutes. This and all other gas usage adds up to a therm a day, 3x my prior usage with stand alone hwh. I'm sure temp will drop less after I insulate the 1.25" steel and 3/4" copper pipes.

But if lowering that cut-in temp will increase risk of Legionnaires, I won't do it.

pecmsg · May 2019

The legionella bacteria is killed @ 140°F, grows rapidly the closer you get to 70°F.

ASHRAE now requires 140° as the minimum temp with 120° maximum at the faucet.

D107 · May 2019

@pecmsg Understood but this is not a standard indirect where the dhw is inside the tank. This is in a coil inside the tank.

pecmsg · May 2019

So...…………..….

There's still a risk!

Tim Potter · May 2019

@D107, you might ping @Mark Eatherton on this, he is a Turbomax user I believe, & has vast experience with Legionnaires.

HVACNUT · May 2019

Every Turbo Max I've ever installed, if boiler limit is 180°, Turbo Max limit is 175°.
If boiler limit is 160°, Turbo Max limit is 155°.
15° on the diff.
120° at the mix.
As far as I know, they're all still kickin'. And if not, it wasn't from Legionnaires.

D107 · May 2019

@HVACNUT We have mix at 110 since for us that's hot enough to mix further at the shower, but perhaps 120 at the boiler mix helps keep Legionnaires growth down in piping between boiler and shower?

D107 · May 2019

@HVACNUT so you set Turbomax Aquastat at the settings you mentioned, regardless of higher water temps measured by the T/P gauge at top of tank. Got it.

hot_rod · May 2019

I doubt any manufacturer would put an anti legionella claim on a tank condition. Common belief is 1 hour at 140F is sufficient to kill bacteria

Any piping with temperatures lower have potential to harbor and grow bacteria in the slime or film inside the tubing or piping

One common protection method is to elevate and circulate the entire DHW piping circuit above 140 for an hour every day

Still you have short sections in supply tubes, dead end piping, etc that mag not get circulated at “kill” temperatures

There is no hard and fast, absolute anti legionella method or system I know of, even chemical treatment has some error potential

D107 · May 2019

@hot_rod Yes makes sense. I'll have to assume the Turbomax engineers made an informed choice to keep the aquastat probe lower in the tank than most indirects. I think in standard indirects aquastat is measuring actual DHW temp, whereas in Turbomax reverse return it measures the tank water temp which by definition must transfer less than 100% of its heat to the dhw inside the coil, which presumably is not quite as hot. So the lower (cooler) probe location compensates for that. Now if only we could get the utilities to stop recommending hot water tanks be kept at 120.

As for on-demand heaters, I found this quote from a manufacturer:

"A tankless water heater does not have the potential to contract and harbour Legionnaires Disease. A tankless completely flushes its system every time the hot water is turned on making it nearly impossible for Legionnaires Disease to repopulate the system."

Not sure about that. (?)

Zman · May 2019

If you are concerned about legionnaires in the sort section of pipe running through the reverse indirect, how are you protecting the rest of your piping?
I would be surprised if your Turbomax keeps up with demand with lower settings that what you have now. No real upside to going much lower.
The sensor location conversation is interesting, I imagine that the tank stratifies considerable when the boiler pump turns off. Who knows what the internal temps are doing.

D107 · May 2019

@Zman I've never really been concerned about the hot water lines going from the indirect to the shower. Though I intend to insulate as much boiler room piping as I can. From the tank's 140-150 we mix down to about 112 and then a few degrees cooler at the shower itself. Maybe I should mix down to 120...I've read a number of HH threads on this; used to keep my direct hwh at 140, so generally I've tried to be safe about it. Reading the answers I've gotten here I'll probaby be even a little more careful with the Turbomax.

hot_rod · May 2019

we have a great, up to date webinar today, regarding Legionella. At noon central time.

https://www.caleffi.com/usa/en-us/education/education#coffee-with-caleffitm

Another option is to install point of use mixers at sinks and two handle tub faucets and run the system at higher temperatures.

It's a catch 22 with DHW these days, especially in public facilities. Scald protection and prevention but also the need for elevated temperatures for bacteria control.

It could be you are more at risk walking past a water fountain or water feature in a park or building then you are with a home DHW system.

Hold your breath when near warm water vapors

ScottSecor · May 2019

Like most on this website, I read most of the articles I come across with regard to Legionaries Disease. According to the CDC the disease is on the rise. https://www.cdc.gov/legionella/images/national-incidence.jpg

As @hot_rod Bob suggests, we are faced with dropping the water temperatures to prevent scalding people while saving energy, but at the same time we're trying to prevent growth inside our systems. I suspect the lower the water temperature idea may be contributing to the problem.

I have no way to prove this, but we have worked at many apartment buildings (public and private) and many schools (public and private) over the years. Almost every one of the larger facilities had massive storage tanks (1000 to 5000 gallon) storage tanks that held dhw at 180 degrees or thereabouts. Most had an internal copper coil that was fed with low pressure steam or boiler water throughout the year. Most (but not all) had a mixing valve that was typically set to 140 degrees for the occupants. Some also had a high temperature dhw supply for slop sinks, mop buckets, laundry, etc. I suspect there were no or very few cases of Legionnaires at these buildings.

Today, we work on systems that store dhw somewhere between 120 and 140 degrees typically (to save energy and prevent scalding). The systems are sized appropriately
and preform well, however I am concerned there could be problems down the road.

D107 · May 2019

@ScottSecor Seems then that if the utilities, manufacturers and state governments could be reached on this matter, it could have a huge impact on the public if they got behind a public information campaign. Managing both the Legionnaires and scalding issues is doable and necessary. "Aquastat at 140, mixing valve at 120." Not rocket science.

ChrisJ · May 2019

hot_rod said:
I doubt any manufacturer would put an anti legionella claim on a tank condition. Common belief is 1 hour at 140F is sufficient to kill bacteria

Any piping with temperatures lower have potential to harbor and grow bacteria in the slime or film inside the tubing or piping

One common protection method is to elevate and circulate the entire DHW piping circuit above 140 for an hour every day

Still you have short sections in supply tubes, dead end piping, etc that mag not get circulated at “kill” temperatures

There is no hard and fast, absolute anti legionella method or system I know of, even chemical treatment has some error potential

Is this even an issue being everything before it should be long dead? Nothing alive should ever get near the cooler piping, no?

hot_rod · May 2019

ChrisJ said:

hot_rod said:
I doubt any manufacturer would put an anti legionella claim on a tank condition. Common belief is 1 hour at 140F is sufficient to kill bacteria

Any piping with temperatures lower have potential to harbor and grow bacteria in the slime or film inside the tubing or piping

One common protection method is to elevate and circulate the entire DHW piping circuit above 140 for an hour every day

Still you have short sections in supply tubes, dead end piping, etc that mag not get circulated at “kill” temperatures

There is no hard and fast, absolute anti legionella method or system I know of, even chemical treatment has some error potential
Is this even an issue being everything before it should be long dead? Nothing alive should ever get near the cooler piping, no?

I suppose on a new system were it was installed bacteria free and the tank or supply was always at elevated temperatures it would be less of a concern.

Older buildings with film or sediment in the piping could harbor bacteria and would need a zap of 140F plus to offer some thermal disinfection.

In a public building it would probably be wise to do occasional testing at various taps to assure it is bacteria free. Kevin indicated legionella testing is more readily available, and affordable now.

i do not think there will be a one solution that fits all buildings. thermal, chemical, UV, maybe a combination of all.

Starting to hear rumblings of legionella potential in cold water supply. Consider areas like Phoenix with public water supplies up to high 80F.

Larry Weingarten · May 2019

Hello, Just to add some confusion, we design and size systems to codes that are way out of date. With reduced water use fixtures, flow rates in pipes are slowing down. This reduces the scrubbing action of higher flows, allowing or even encouraging bio-films to build up. These films harbor Legionella and other bugs. Our energy and plumbing codes are not aligned and really need to be. The take-away is to size piping as small as you can get away with so you often get one foot per second or more. Commercial lavatories with adequate pressure could be served with 1/8" tube, but you're not likely to see it, and 1/4' could work in lots of places where we use 1/2".

Yours, Larry

pecmsg · May 2019

Legionella Bacteria is a natural and is found in the public water supply. The problem arises when the water reaches the bacteria's Bloom range roughly 95 - 115°F.

https://www.cdc.gov/legionella/wmp/overview/growth-and-spread.html

These levels are made worse when air born giving the bacteria direct access to the lungs. (you need to inhale it to get it)Showers, Water mists (Cooling Towers).

Jean-David Beyer · May 2019

I put in a temperature mixing valve after my hot water (triangle-tube tank within a tank) heater before the hot water goes to the rest of the house. I put a dial thermometer in the hot water supply line and another in the mixed delivery line. I turned on the hot water to the shower-bathtub full on, and adjusted the hydrostat on the hot water heater until the hot water was never less than 140F. The boiler supplies 190F +|- 5F water to the indirect. This meant that it went up to 160F sometimes, but the mixing valve had no trouble with that. It supplies 120F to the house. Unfortunately, it never gets that high at the points of delivery because my 1/2 inch pipes are all buried in the concrete slab, along with those running the radiant floor heat. So while there may be no live bacteria coming out of my hot water tank, and perhaps none in the mixed 120F water supplied to the house, I very much doubt that any bacteria in my 70 year old internal plumbing will be killed by the 110F to 120F that passes through those pipes.

ScottSecor · May 2019

Heck of coincidence that this article shows up locally, even made the NYC morning news. Hope they find the cause real fast. Think I may crank up my Turbomax for an hour or so and then flush every faucet in the house just as a precaution.
https://www.tapinto.net/towns/clark/articles/three-cases-of-legionnaires-disease-in-clark-22-in-union-county

D107 · May 2019

@ScottSecor Which reminds me to mention that when I turn off my boiler during a summer vacation, when I come back I always flush all the house faucets before using any hot (or cold water too?). Even if the flushing is with 120 degree water, that should push out any bacteria colonies in the stagnant water. Just once I'd like to see in articles like the one you posted in their list of preventive measures to raise the dhw tank temperatures.

Legionnaires Disease An Issue With Reverse Indirects?

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