!40 Degrees F is the requied temperature to kill Legionella Bacteria.Temperature affects the survival of Legionella, as follows:
At 60 °C (140 °F) - Legionella dies instantly - pasteurisation occurs.
At 55 °C (131 °F) - 95% die
50 to 55 °C (122 to 131 °F) - Can survive but do not multiply
35 to 46 °C (95 to 115 °F) - Ideal growth range
20 to 50 °C (68 to 122 °F) - Growth range
Below 20 °C (68 °F) - Can survive but are dormant, even below freezing
From published Health and Safety Executive guidance for employers in the United Kingdom http://en.wikipedia.org/wiki/Legionella
I got that from www.Legionella.org Here is an intresting little tidbit from their site as well about Tankless water haters. Note they flash the water to 190º then temper it back down, then learned the leginella was growing in the pipes downstream from the heaters.A minimum temperature of 60°C is required to kill Legionella bacteria in hot water systems (the higher the temperature the shorter the required contact time)
Would you be able to comment on tankless heaters and the efficacy of holding them to a standard promulgated specifically to reduce Legionella risk?We once thought, as you suggested, that elimination of the large volume hot water heater would significantly reduce Legionella colonization in the hot water system. In a survey of 15 hospitals in western Pennsylvania, in 2 hospitals with instantaneous steam heating systems (tankless heaters) no Legionella was isolated from these hospitals. We then replaced the 1000+ gallon hot water tanks in one of our VA hospitals with instantaneous heaters in an effort to decrease Legionella colonization. These heaters flash heated the cold water to 190o and then blended the water back down to the pre-set temperature (which was 140oF). Disappointingly, this installation had virtually no effect on the downstream colonization of fixtures. We now understand that the entire network of pipes is coated with a slime layer (biofilm) within which Legionella resided. The bulk of the Legionella colonization of the water system was downstream of the hot water tanks! This is why active disinfection throughout the system is required to control Legionella bacteria in warm water systems. So, if the temperature of the blended water as it exits from the tankless heater is 140oF, then that should satisfy the Health Department’s objective.
Tankless standby temperatures are room temperature. Old and stagnant water is 100% flushed out of the heater every time it is used. After the water heating cycle, a tankless will also heat the water in the heater above 140 degrees.
Tank water heater and distribution system temperature recommendations are listed here.
DOMESTIC HOT-WATER SYSTEMS.
Background. Domestic hot-water systems are frequently linked to Legionnaires' outbreaks. The term "domestic" applies to all nonprocess water used for lavatories, showers, drinking fountains, etc., in commercial, residential, and industrial settings. Disease transmission from domestic hot water may be by inhalation or aspiration of Legionella-contaminated aerosolized water. Water heaters that are maintained below 60°C (140°F) and contain scale and sediment tend to harbor the bacteria and provide essential nutrients for commensal micro-organisms that foster growth of L. pneumophila. Large water heaters like those used in hospitals or industrial settings frequently contain cool zones near the base where cold water enters and scale and sediment accumulate. The temperature and sediment in these zones can provide ideal conditions for amplification of the organism. Dead legs (i.e., sections of piping or plumbing that have been altered or capped such that water cannot flow through) and nonrecirculated plumbing lines that allow hot water to stagnate also provide areas for growth of the organism.
Design. Water systems designed to recirculate water and minimize dead legs will reduce stagnation. If potential for scalding exists, appropriate, fail-safe scald-protection equipment should be employed. For example, pressure-independent, thermostatic mixing valves at delivery points can reduce delivery temperatures. Point-of-use water heaters can eliminate stagnation of hot water in infrequently used lines. Proper insulation of hot-water lines and heat tracing of specific lines can help maintain distribution and delivery temperatures.
a. To minimize the growth of Legionella in the system, domestic hot water should be stored at a minimum of 60°C (140°F) and delivered at a minimum of 50°C (122°F) to all outlets. The hot-water tank should be drained periodically to remove scale and sediment and cleaned with chlorine solution if possible. The tank must be thoroughly rinsed to remove excess chlorine before reuse.
b. Eliminate dead legs when possible, or install heat tracing to maintain 50°C (122°F) in the lines. Rubber or silicone gaskets provide nutrients for the bacteria, and removing them will help control growth of the organism. Frequent flushing of these lines should also reduce growth.
c. Domestic hot-water recirculation pumps should run continuously. They should be excluded from energy conservation measures.
a. Raising the water-heater temperature can control or eliminate Legionella growth. Pasteurize the hot water system by raising the water-heater temperature to a minimum of 70°C (158°F) for 24 hours and then flushing each outlet for 20 minutes. It is important to flush all taps with the hot water because stagnant areas can "re-seed" the system. Exercise caution to avoid serious burns from the high water temperatures used in Pasteurization.
b. Periodic chlorination of the system at the tank to produce 10 ppm free residual chlorine and flushing of all taps until a distinct odor of chlorine is evident is another means of control. In-line chlorinators can be installed in the hot water line; however, chlorine is quite corrosive and will shorten the service life of metal plumbing. Control of the pH is extremely important to ensure that there is adequate residual chlorine in the system.
c. Alternative means to control Legionella growth include the use of metal ions such as copper or silver (which have a biocidal effect) in solution. Ozonization injects ozone into the water. Ultraviolet (UV) radiation also kills microorganisms. Commercial, in-line UV systems are effective and can be installed on incoming water lines or on recirculating systems, but stagnant zones may diminish the effectiveness of this treatment. Scale buildup on the UV lamp surface can rapidly reduce light intensity and requires frequent maintenance to ensure effective operation.
Last edited by Ladiesman271; 07-14-2009 at 06:41 AM.
Samuel James Witwicky
No anode rod, so no metal accumulation. There is no concentrated mess of goop stored in a tankless heat exchanger. An 8 year old tank type water heater has 8 years of accumulated gook stored in the tank.
Whatever "crap" runs through a tankless water heater is no different than what runs though the cold water tap.
Samuel James Witwicky
Section 890.1210 Design of a Building Water Distribution System
a) Design and Installation. The design and installation of the hot and cold water building distribution systems shall provide a volume of water at the required rates and pressures to ensure the safe, efficient and satisfactory operation of fixtures, fittings, appliances and other connected devices during periods of peak use. No distribution pipe or pipes shall be installed or permitted outside of a building or in an exterior wall unless provisions are made to protect such pipe from freezing, including but not limited to wrap-on insulation or heat tape tracer line or wire.
Hint on peak water temperature in the heat exchanger. What is the coolant temperature in your truck's engine after you turn off the engine?
What is growing in your household cold water pipes? Same water temperature!
In addition with each use of hot water in a tankless system, by the time hot water gets to the point of use in a private home all of the "stagnant" water has been flushed from the heater and the hot water distribution pipes.
If you use 1/2 of the water in a tank heater you don't have hot water anymore. You do end up with a 1/2 a tank of "old" water mixed with some "new" water. Water in the hot water distribution pipes is never flushed but is just replaced with water stored in the hot water tank.
Commercial buildings like a hospital are hardly comparable to a home hot water system.
We had that discusion before. What is the legal definition of "peak use"? The prior answer was it all depends!
I think that adequate for the intended use is the term that is used in codes in my area.
Last edited by Ladiesman271; 07-14-2009 at 08:41 AM.
Samuel James Witwicky
Not really. You are starting from a hot water going to warm which is more an ideal growing temperature than cold water.What is growing in your household cold water pipes? Same water temperature!
If you keep the tank hot enough like in the Bradford White model GX-2-25S6BN Which stores the water at 180º and distributes it at the set temperature of 120º Yes it may be a small 25 gallon tank but it can provide 155 gallons of hot water in the first hour. Its big brother GX-1-55S6BN which is a 55 gallon tank can give you 200 gallons of hot water in the first hour.In addition with each use of hot water in a tankless system, by the time hot water gets to the point of use in a private home all of the "stagnant" water has been flushed from the heater and the hot water distribution pipes. If you use 1/2 of the water in a tank heater you don't have hot water anymore.
Well you are right and you are wrong. Yes a home will not have as long of a distance from the tankless units to the fixtures. But things still can grow in the lines after the tankless system. Also if you think about it lots of people only set their tankless to 115º to 120º which is the ideal temperatures for things to grow in it. Please do not be under a false sense of security that you or your family can not get sick just because you got rid of the tank.Commercial buildings like a hospital are hardly comparable to a home hot water system.
Peak use is all the fixtures turned on at once. If you do not believe me call your local plumbing inspector and ask them what they consider as peak flow per the code.We had that discusion before. What is the legal definition of "peak use"? The prior answer was it all depends!
Oh and the minimum water pressure at all the fixtures during this peak flow is to be at least 8 p.s.i. per the code again. When you open more hot water taps in the home and if the tankless system is undersized it will restrict the flow rate so it can still deliver hot water. I have seen installs where when people opened 3 hot water taps I be lucky to see a trickle come out of the fixtures.
Any documantation of your theory? The water temperature will rise after the water flow stops!
A tankless water heater does not store hot water. Cold and hot water pipes will equalize at room temperature, so they are both the same temperature when not in use. A tank water heater never cools down.
Don't you need a 3/4 inch gas feed for those? I would have to install a new vent also. You know, that looks to be as expensive as a tankless installation!
You also forgot about all the crap that settles in that a tank water heater. 180 degree water storage temperature makes things much worse. That temperature setting conflicts with this recommendation: "** Excessive lime scale formations can also be reduced by setting the water heater temperature control at the lowest possible temperature which will provide satisfactory hot water service. The usage of water softening equipment greatly reduces the hardness of the water. However, this equipment does not always remove all of the hardness (lime). For this reason it is recommended that a regular schedule for deliming be maintained."
"The amount of calcium and magnesium carbonate (lime)
released from water is in direct proportion to water
temperature and usage, see chart. The higher the water
temperature or water usage, the more lime deposits are
dropped out of the water."
Tankless heaters do not store water at 120 degrees. The water temperature in a tankless is room temperature the vast majority of the time. Hardly the "ideal" temperature for things to grow in. Same temperature as the hot and cold water pipes.
Adequate for the intended use if the general wording of the various codes here.
Last edited by Ladiesman271; 07-14-2009 at 09:48 AM.
Samuel James Witwicky