[Greenbuilding] Low powered (wattage) water heaters availablethrough Hydro Quebec
obrien at hevanet.com
Fri Dec 30 11:54:38 PST 2011
I've read some of the research on Legionella in hot water systems, and here's what I think I learned so far:
--Gas water heaters and boilers don't harbor Legionella at 120 F/49 C, because of the way they heat stored water from the bottom.
--Electric water heaters do sometimes harbor Legionella in the sediment that collects on the bottom of the tank, where the temperature is lower than in the water above.
--Stagnant water in distribution pipes, such as underfloor hydronic loops in summer, can harbor Legionella. Possibly a reason to separate domestic hot water from heating water, and to have a recirculating system for DHW.
--Raising the tank temperature from 120 to 145 F or 49 to 60C does not guarantee Legionella will be killed, especially in the distribution system.
My own conclusion is that *only* raising tank temperature is not an effective strategy, especially in electric tanks; better to eliminate stagnant cool spots in the tank and distribution pipes. However, I'm certainly open to other views.
On Dec 30, 2011, at 11:03 AM, Corwyn wrote:
> On 12/30/2011 1:35 PM, RT wrote:
>>> - Keep your water heater’s temperature at 49°C (120°F).
>> Probably not the best idea to save a few pennies, recalling a previous
>> discussion on this List where one Maritimer had the heebie-jeebies about
>> the high potential for legionella contamination even when the thermostat
>> is set for 60 degC
> Thank You Kindly,
> Topher Belknap
> Green Fret Consulting
> Kermit didn't know the half of it...
> topher at greenfret.com
> (207) 882-7652
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