Hard data for Legionella growth in open direct systems?
Last Post 21 Feb 2014 10:06 AM by sailawayrb. 48 Replies.
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ZadUser is Offline
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04 Feb 2014 12:03 AM
My wife and I are in the planning stages of a renovation that will give us in-floor radiant heat (and I can't wait…no more cold feet). I have been reading about closed vs open direct systems and I understand the basics and the potential risks involved with open direct. At the same time, I like the simplicity and efficiency of the open direct system. I am curious if there is any research data on the growth of Legionella in open direct systems…I haven't been able to find any. What I have found is a series of papers in various journals (all medical and public health related) which show that Legionella is found in 40% of all electric hot water tank systems and 0% of fossil fuel heated hot water tank systems (apparently electric hot water tanks have cooler regions of hot water in them than do gas/oil/propane hot water tanks that allow Legionella to grow). I can provide these references if wanted. So it makes me wonder how the rate of Legionella contamination in open direct systems compares to electric hot water tanks. Even more specific, I wonder if there is any data comparing open direct systems with electric (not even sure if such a thing exists) and gas/propane/oil? Is there any data on the frequency with which people get sick using open direct systems? If I were a betting man I would wager that open direct systems are no more dangerous than domestic hot water heated by electric hot water tanks…but this is just a guess as I can't find any real data to ground this topic in science. If any of you know of this research, please point me toward it.
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04 Feb 2014 01:20 AM
First let me say I prefer boiler closed loop systems.
Should you chose an open loop,
Keep in mind how you might cycle water daily, spring and summer, Taco make a great pump controller that will exercise the pumps daily for a short amount of time, not a bad choice.
Storage tank temp, I think the magic number is 140 degrees, kills bugs.
Looks like your own due diligence shows a 40% rate in electric tanks, there is more info out there.
Check the CDC
Dan
Dan <br>BlueRidgeCompany.com
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04 Feb 2014 08:19 AM
We have been running an open system for 12 years now. I did lots of research on Legionella and could find no hard evidence. More cases of legionella are found in systems with dead legs rather than small open circulation systems.
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04 Feb 2014 08:58 AM
You are correct, there is little evidence to support that Legionella occurs in active open HR systems that use water that has been chlorinated. As you say, this is not really any different than a normal domestic hot water system. The key being that the HR system must remain active. You can’t turn off any circuits or the circulator pump(s) for extended periods of time.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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04 Feb 2014 09:55 AM
The CDC has lots of general information about transmission, growth environments, death rates etc but nothing that I can find on open systems. One concern I had was whether or not pex increased the risk of biofilm formation and legionella and over the long haul, there is no difference between pex and other plumbing materials. It seems to me that there is a bit of a black hole of evidence here other than individual uses and their experience. I am in health care and this topic reminds me of the research on flu vaccine effectiveness. The vast majority of the research showing that flu vaccines work comes from industry (i.e.: the people that make the vaccine). Non-industry research tells a very different story. Even including industry research, which skews the data toward the more favourable, the totality of the data tells us that in order to prevent one case of flu you have to vaccinate 30 to 100 people. In other words, it is protective 1 - 3% of the time. And, any time you get a flu shot you increase your risk of Guillain Barre. Despite this very solid evidence, the public health medical mantra is get the flu shot. It is interesting to me how so much of what we do on a daily basis is driven by what has been done in the past regardless of the presence or lack of evidence. I will keep scouring for a research paper that looks at the open direct/legionella issue.
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04 Feb 2014 10:48 AM
Here is an interesting CDC article
http://ajcc.aacnjournals.org/content/12/3/234.full
Opening paragraph says it all
"According to the Centers for Disease Control and Prevention, although 18 000 to 25 000 cases of pneumonia due to Legionella pneumophila occur each year, the diagnosis is reported in only 1200 to 1500 cases because of the nonspecific signs and symptoms of the disease and inadequate testing for Legionella. This case study presents information about the epidemiology, pathophysiology, clinical features, and treatment of legionnaires disease and emphasizes the importance of early diagnosis."

So reality is that it is there, but presents its self as a Pneumonia. I read another CDC report regarding misdiagnosis and potential death rates in hospitals,due to legionella in the DHW systems.
There is a lot of information about legionella, but very little about it in relation to open loop systems, perhaps due to the small interest in funding a study like that.
So a person must draw there own conclusion and solutions.
Its real, and out there.
Not sure all water systems are chlorinated. My well is not.....
Dan
Dan <br>BlueRidgeCompany.com
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04 Feb 2014 11:12 AM
Yes, I did read that CDC info and it is definitely the case that many, if not most, cases of Legionella are missed due to lack of testing. We do know that Legionella is ubiquitous in water environments and that the vast majority of people who get sick from it are already compromised in some way.

What I am so curious about is how legionella contamination in electric hot water tanks compares to contamination in open systems. I do appreciate that there would be very little financial or public health incentive to study this given the very small numbers with open systems. However, given that the bulk of evidence shows 40% of electric hot water tanks are contaminated with the bug it would be really nice to have a real world comparison to open systems.

Electric hot water tanks are not widely perceived, to my knowledge, as being a public health risk. I have never heard of a plumber not wanting to install a electric hot water tank due to the risk of Legionella. If the contamination rates between electric tanks and open systems are the same, or even close, it would really lend credence to the open system given the overall safety of electric hot water tanks despite the high degree of contamination.
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04 Feb 2014 12:01 PM
I am certain that not ALL water systems are chlorinated…and that you should NEVER operate an open HR/domestic hot water system if your water has not been chlorinated or otherwise properly treated. Some folks have health concerns about drinking water from chlorinated water systems and that is not an unfounded concern either.

All the wells on all of our properties are properly chlorinated using a Stenner peristaltic pump and appropriate contact time tank. If properly chlorinated, there is only a small amount of residual chlorine left over from this sterilization process at this point. All of the house water then receives sediment and carbon filtration which removes this remaining small amount of residual chlorine. The drinking water also receives UV sterilization, reverse osmosis, and additional carbon filtration.

There have been studies that show there is a much higher incidence of various cancers from drinking well water that has not been properly treated. This is believed to be the result of ingesting low levels of various elements such as arsenic over a period of time.

I would personally not be too concerned about using an electric hot water heater that is being fed water that has been properly treated. However, I would personally be very concerned about using any water heater that is being fed water that has not been properly treated.

It really doesn't matter what folks on a forum such as this recommend. What matters is what your building authority requires.  They are also often knowledgeable about local issues requiring extra attention and due diligence.
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04 Feb 2014 01:08 PM
Good points sailawayrb. Our city water is chlorinated and, if I am understanding you correctly, this will dramatically reduce the incidence of Legionella even in an electric hot water tank or an open direct system?
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04 Feb 2014 05:14 PM
Yes, chlorination is a very effective preventative and treatment for legionella. 0.5 ppm residual chlorine in hot water systems is considered an effective preventative. If you have a system with a known legionella problem, temporary chlorination shock treatment at or above 2 ppm for 24 hours is an effective treatment. You can purchase a chlorine test kit for a couple of dollars to determine your residual chlorine level. If necessary, you can also increase the chlorine level of just your hot water system as I described previously using Clorox bleach.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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04 Feb 2014 09:46 PM
Some interesting reading.

http://www.healthyheating.com/water_heaters_as_boilers.htm#.UvGgfijhGS0
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05 Feb 2014 05:42 AM
FBBP, thanks for the link. I had found that site about a week ago and read all the research papers listed at the bottom of the page. None of the evidence presented pertains to open direct systems except for the obvious opinion of the website author. What is disappointing to me is that the website is clearly anti-open direct and yet all the evidence presented does not contain one shred of data supporting the idea that open direct is dangerous. There are numerous references to any given electric hot water tank having a 40% chance of being contaminated with Legionella but absolutely nothing on open direct. This site is a classic example of an opinion masquerading as a well substantiated position using totally unrelated data to support the opinion. So frustrating. At the end of the day, what I am left with is the fact that I could easily have an electric hot water tank installed in my house today without any question about safety, despite the well documented risk of Legionella exposure. If I were to ask for an open direct heating system to be installed, however, I would likely be met with stiff resistance due to completely unsubstantiated perceived risk. As a layperson to the plumbing and heating industry, this makes absolutely no sense to me. What am I missing?
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05 Feb 2014 08:22 AM
From what I understand, the two key aspects of completely reducing the risk of Legionella is using a fossil fuel fired heater and heating the water to 140 F or 60 C. Wouldn't the perfect and safe solution for an open direct system, then, be turning the appliance up to heat the water to 140 F and then using mixing valves downstream to lower the temperature of the water to the taps and floor to 120 F?
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05 Feb 2014 08:54 AM
What you are missing is that there are many “pros” who are highly motivated to discourage DIY HVAC and plumbing. They would prefer to charge you an order of magnitude more for a project and profit from it. You really can’t blame them from being motivated to do this as this is how they make their living. Unfortunately, there are also many “pros” that are not even as competent as the average motivated DIYer too. This why most building authorities allow anyone to do their own HVAC and plumbing on their own homes as long as they follow the code and pass inspection.

How do you know that 120F is what you need for your HR floor? Have you done a proper building heat loss analysis and have you done a proper HR design? Buildings with well insulated and sealed envelopes typically use supply temps below 100F for HR floors. We have free DIY software on our website which would enable you to do both if you have not done so already. There are also detailed instructions for properly using the software to accomplish the analysis and design.

As I indicated previously, a small amount of chlorine will address this issue just as well as operating at high temp.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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05 Feb 2014 11:06 AM
sailawayrb, wow, that is some calculator. I have done nothing like that, just a total building heat loss calculation. Thank you for the link, I will pick away at it today.
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05 Feb 2014 11:17 AM
Thanks Zad. Something else for you to consider…

When heat sources are combined with zoned HR distribution systems, it is possible for the heat source to short cycle when only a couple of these zones call for heat. This occurs because the rate of heat produced by the heat source may be much greater than the rate of heat used/released by these zones. Some heat sources in combination with low hydronic fluid volume HR distribution systems cannot absorb this excess heat rate without experiencing a rapid rise in temperature. This causes the heat source to reach its high temperature limit very quickly resulting in very short on times and short cycling. While electric heating elements can tolerate short cycling, gas valves, oil burners, ignition systems, and compressors will have a significantly reduced life expectancy.

So an electric hot water heater may be a better choice than a gas fired hot water heater with regard to this issue. You can also easily replace many electric hot water heaters for the cost of what a “pro” will charge you to install a gas fired boiler. So while we typically prefer/recommend boilers over most heat source options for HR applications and we always recommend a closed HR system over an open HR system, for a competent budgeted minded DIYer, an electric hot water heater may be a good DIY heat source option.  As is always the case, doing a good ROI analysis for your specific situation parameters will confirm this.  Again, you have to properly determine the BTUs in order to size and access the feasibility of using the heat source being considered.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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05 Feb 2014 11:40 AM
Posted By Zad on 05 Feb 2014 05:42 AM
FBBP, thanks for the link. I had found that site about a week ago and read all the research papers listed at the bottom of the page. None of the evidence presented pertains to open direct systems except for the obvious opinion of the website author. What is disappointing to me is that the website is clearly anti-open direct and yet all the evidence presented does not contain one shred of data supporting the idea that open direct is dangerous. There are numerous references to any given electric hot water tank having a 40% chance of being contaminated with Legionella but absolutely nothing on open direct. This site is a classic example of an opinion masquerading as a well substantiated position using totally unrelated data to support the opinion. So frustrating. At the end of the day, what I am left with is the fact that I could easily have an electric hot water tank installed in my house today without any question about safety, despite the well documented risk of Legionella exposure. If I were to ask for an open direct heating system to be installed, however, I would likely be met with stiff resistance due to completely unsubstantiated perceived risk. As a layperson to the plumbing and heating industry, this makes absolutely no sense to me. What am I missing?


Zad - I was wondering if your code is the same as Alberta's and that it prescribe a minimum run time? I think that is the key. I understand your frustration with rules with no back ground. If something is said often enough, it just gets parroted by people who have no idea of why, until it is commonly accepted as gospel.
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05 Feb 2014 11:40 AM
Maybe there's a lack of evidence on this because its not worth anybody's time to test the hypothesis that an open system breeds a Legionella when an open system doesn't have many advantages to make it worth testing that hypothesis in the first place.

And if your expecting to experience warmth in your feet in a radiant system then the system is probably being used in the wrong way.
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05 Feb 2014 11:41 AM
http://www.cdc.gov/washington/testimony/2013/t20130205.htm
Read this,
Dan
Dan <br>BlueRidgeCompany.com
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05 Feb 2014 11:52 AM
It's true you can get a lot of things installed here in north america for DHW with no regard for bacterial amplification.

What's interesting is that European equipment, however, often has a lot more features in this regard. The Altherma DHW tank, for example, has a 'sanitation' function which elevates the tank temperature significantly for a scheduled time period every week. you can increase it's frequency but you CAN NOT TURN THE FEATURE OFF. Which leads me to believe that either european codes address this concern directly, or at least one major multinational corporation (Daikin) has decided that the potential risk to their clients (and thus litigation) is significant enough to bypass with some certainty in this respect.

As ergnut says though, there is not enough benefit in going open to make it worth worrying about disease: the risk to your system components itself is worth the cost of separation by itself. One time fee insurance is generally the best deal you'd ever get in risk mitigation. And I've seen more than a few open direct system failures related both to grounding issues as well as water quality issues... quite simply, it's not worth it, and trying to justify cutting this particular corner is misguided.

water heaters can be great solutions in some cases. but separate the fluids.
Rockport Mechanical<br>RockportMechanical.com
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