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Legionnaires Disease Q's

Tim Potter
Tim Potter Member Posts: 273
Questions in regards to Legionnaires Disease,

1) Do you (re)design your Hot Water system any different with well water vs city water?

eg: Do I need to worry about LD If I'm on well water, or does LD know no bounds and is in all water?

2) Do you design your system any different with Tankless vs a Tank type WH.

Does going through a tankless set at 140* and tempering down to 120* 'kill' the LD or does the water need 'some time' at 140* to fully kill the bug, or does it even matter with a tankless. (I'm assuming that Indirect, Gas, and Elect are similar for the purpose of this example. Pls correct me if I assume wrong)

My setup:

1)Main House, Metro KC, city water, 3 showers, Traditional 50Gal Gas WH, set on low, brings the water up to about 85* then through a Bosch Tankless 120,000btu brings it up to 120* to the house. with this setup we can run at least 2 showers at the same time.

2) Lake cabin, Well Water, 2 Showers, 199,000btu tankless 55* to 65* out of the ground, tankless set to 120* but setup to temper water back to 120* if higher water temp needed. this will run at least 2 showers at a time.

3)Colorado Mtn House, City water, 3 showers, Indirect 80G off 120,000 btu Boiler, when we are not there (long periods of no occupancy) water goes to ambient (55 in winter, whatever in summer, 65 or so) then we arr and set Ind to 120*, no tempering on that unit. runs at least 2 showers at a time with fast recovery.

I am wondering if I need to change anything to do things differently.

Thank You for your input:

Winter Park, CO & Arvada, CO


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853


    The bacteria responsible for Legionaires disease is omni present in the dirt and the water. Does not matter if you are on country wells or city water distribution. A study by the CDC found that 90% of those tested had been exposed to the bacteria, probably through drinking it. Drinking it will not cause any ill effects. The amount of chlorine based oxidizer required to eradicate the bacteria would need to be probably 10 times greater than the minimum required levels, and would definitely cause other problems (health and mechanical)

    You can suppress the bacteria through cooling (chill the water to below 50 degrees F) scald sanitization (maintain storage and distribution systems above 140 degrees F) or the use of a silver based oxidizer along with an ultrasonic conditioner (possible negative health benefits).

    The most reliable, as proven by the Europeans, is scald sanitization.

    The bacteria requires certain "ideal" conditions in order to grow and multiply. Storage tanks held at low (thin petrie dish) conditions are ideal. It also requires food and oxygen, all of which are present in potable water. Under ideal conditions, the bacteria multiplies and becomes a problem for people with depressed immune systems, who inhale the bacteria in droplets of water (typically a shower). They set into the microphages and show up in the form of bacterial pneumonia. It has a kill rate of around 10%.

    A tankless water heater can not provide the ideal growing conditions for the most part. An indirect or self contained water heater can.

    The amount of contact time to reduce the bacteria count is a function of temperature and time. In your case, the 85 degree preheat tank is providing an ideal condition for growing the bacteria, and with it passing through the tankless at the rate that it does, it will lessen the bacteria count, but will not eliminate it.

    You would be better off to maintain the tank heater at 140 degrees F., and could do this with properly placed pipes and pump using the tankless as the heat source, allowing you to block off the flue gas passage ways of the wasteful tank type heater, thereby eliminating its flue losses. Bradford White (the company, not the engineer) did some studies and determined that the cost of operating a typical tank type water heater at 140 degrees F versus 120 degrees F was worth about $1.00 per month. Worth the money if you ask me, to protect yourself and your family from this deadly disease.

    We as an industry are fighting an uphill battle. We have utility company telling people (due to litigation potentials) to keep their settings below 120 degrees F, and we are telling them to turn it up to 140 degrees F and mix it down to 120 degrees F to avoid scald exposure to the end users. Not an easy battle.

    Homes that use a DHW heater as their heat source AND are using the same water for showering and bathing are exposing the users to significant quantities of the bacteria. In fact, I am aware of at least three people (not including myself) that have contracted LD from systems set up exactly as I described. The killer is, IT IS STILL CONSIDERED LEGAL TO DO SO... In the US and Canada.

    Fortunately, slowly but surely, local AHJ's are getting smarter and enacting the "Equal to or greater than" restrictions and outlawing this deadly use. Flushing will not work (as some manufacturers would have you believe) nor will pump "exercising". It should just plain and simple be illegal to do so. In fact, depending upon your interpretation, IT IS ILLEGAL to do these combination systems, because the installer has compromised the integrity of the potable water distribution system.

    On your home in WP, I'd suggest you maintain a higher tank set point (140 degrees F), mixing down with anti-scald valve and allow it to operate for at least 2 hours at 140 degrees F prior to use.

    Your cabin should be OK.

    Watched 100 plus professional cyclist CRUISE past my home up here in Heeney yesterday. Might have put it on the map... NOT!!



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  • BobC
    BobC Member Posts: 5,479
    Saw it a few years back

    The mail processing facility in Boston had someone come down with Legionnaires disease about 5 years ago. This plant is about 40 years old and has been knuckle-headed many times over. After an investigation by the CDC they found there were piping stubs, some 20 feet long, where water just sat for years. The feeling was those stubs were a great place to grow something like this.

    So in addition to keeping the water heater hot make sure all the piping sees water flow so the pipes stay flushed.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
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