Hot Water Cylinders and Legionella

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pctek

807 posts

Ultimate Geek
Inactive user

#1856777 1-Sep-2017 15:51

70 to 80 °C (158 to 176 °F): Disinfection range
66 °C (151 °F): Legionellae die within 2 minutes
60 °C (140 °F): Legionellae die within 32 minutes
55 °C (131 °F): Legionellae die within 5 to 6 hours
Above 50 °C (122 °F): They 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): Legionellae growth range
Below 20 °C (68 °F): Legionellae can survive but are dormant

Kickinbac

427 posts

Ultimate Geek

#1857007 1-Sep-2017 22:58

For what its worth, I just did a project for an aquatic centre. The domestic hot water is heated continuously by geothermal hot water at approx 46 degrees C. The hot water cylinders have electric elements on a timer set to heat to 65 degrees daily between 11pm and 5 am specifically to kill legionalla. This was based on a hydraulic specification by a consultant. All the showers and basins had tempering valves.

ermat

172 posts

Master Geek

#1857418 3-Sep-2017 06:48

So depending on what type of hwc you have, some may be more suited than others to dealing with legionnaires when being turned off for long periods of the day. Like wether its 1 element or 2 ?
Any thoughts on what hwc I should use in my new house with this daily timer shutdown in mind. Its a larger house that requires a 250 (approx) cylinder.

timmmay

20574 posts

Uber Geek

Trusted

Lifetime subscriber

#1857420 3-Sep-2017 07:01

On Flick we only heated the water 2-5am and didn't have a problem. That may be because the water's chlorinated. Now we're on Electric Kiwi with our free hour 5am we have the hot water cylinder heat 9am to 4pm, with the idea that late afternoon / evening water use will be heated in the free hour.

In general I think better safe than sorry with this stuff.

MrLucas

4 posts

Wannabe Geek

#1858102 4-Sep-2017 13:35

Hey have read through this topic and wanted to know from maybe Aredwood (plumber?) Would continuous gas water heaters suffer from this issue if it had a ring main/recirculation system attached?

As they only heat to temperature you want, water in the ring main even if only a few litres is being re heated to that temp or do the bacteria need stored settled water not continuously flowing to become a problem?

MikeAqua

7773 posts

Uber Geek

#1858185 4-Sep-2017 14:30

Bacteria need three main things to reach dangerous concentrations: -

1) The right temperature range (proliferation is related to temperature); and

2) Nutrients - Legionella are pretty versatile on this; and

3) Accumulation - there needs to be somewhere for them to accumulate to sufficient levels to deliver an infectious dose.

(1) Is the easiest thing to control. And it's easy enough to knock down a population once per day by heating the whole cylinder well. After that they will struggle to accumulate enoguh to be dangerous.

The two biggest risks of Legionella are

(A) Soil/compost (older people often get infected this way).

(B) Refrigeration/HVAC cooling systems.

(B) Tends to cause clusters of cases: Some chump allows their cooling system to accumulate a lot of scale, rendering treatment ineffective; or simply fails to treat it altogether. Legionella flourishes and aerosol of contaminated water infects passers by.

Old, very young and immune-compromised people are most at risk from Legionella.

Mike

Aredwood

3885 posts

Uber Geek

#1858420 4-Sep-2017 20:26

MrLucas: Hey have read through this topic and wanted to know from maybe Aredwood (plumber?) Would continuous gas water heaters suffer from this issue if it had a ring main/recirculation system attached?

As they only heat to temperature you want, water in the ring main even if only a few litres is being re heated to that temp or do the bacteria need stored settled water not continuously flowing to become a problem?

@MrLucas Yes ring mains can definitely have legionella issues. It is in the plumbing codes now that ring mains must operate at at least 60deg. There are earlier installations that ran via a tempering valve. (which often wouldn't work properly anyway) And now cannot be installed (tempered ring mains). I have also seen ring mains using UV disinfection, But that is not a guaranteed solution. As the UV unit will only kill legionella that are inside the unit.

Just because a heat source is a gas continuous water heater, if there is a ring main. Then the whole ring main must be kept over 60deg. Continuous flow water heaters without a ring main are ok at any temp. As the heater and pipes cool down to room temp when the heater is not in use.

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