Evohome hot water settings to prevent legionella

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  • mazzy89
    Automated Home Jr Member
    • Nov 2020
    • 44

    Evohome hot water settings to prevent legionella

    I've been quite surprised that I haven't find any mentions about goods settings for the evohome hot water kit that would prevent the legionella in our hot water cylinders.

    It's important to save money and I think evohome is great in that but what about prevention of legionella? For instance Google Nest has a functionalities right for that.

    So since there is no settings how do you guys manage your schedules?

    It it ok to leave off for like 3/4 hours the hot water heater? Is it safe? Or I should continuously heat the water to prevent this bacteria? Which is your approach?
  • GreenGuy
    Automated Home Jr Member
    • Jun 2018
    • 26

    #2
    Health and Safety Executive
    Provides links to sources of information and guidance on health and safety in the health and social care services sector.

    Comment

    • mazzy89
      Automated Home Jr Member
      • Nov 2020
      • 44

      #3
      Yes, thank you GreenGuy for the link. I have found it before too ;-)

      However, this does not reply to my question. the rules says the temperature must always be over 60C.

      It means that the heater must be continuously turned on because it is physically impossible to keep the water there inside w/ a temperature above 60.

      This takes me to my question. Despite these regulations in reality how do you program the schedules of your hot water evohome kit?

      Comment

      • therealfronty
        Automated Home Guru
        • May 2021
        • 140

        #4
        I have my DHW set to 55 degrees, and the schedule gives it a blast early in the morning for my shower and then late afternoon so the wife can do some washing when she gets back from work then a final blast in the evening for the kids showers. The temperature drops below 40 degrees during the day but when it's heated it'll kill off any bacteria, you don't need to keep it heated all day long. I have experimented and found that 60 degrees was too hot, also there's "stratification" occurring inside the cylinder, so the temperature at the top of the cylinder will be higher than 55, it certainly feels above 60 when it comes out of the hot water tap. I've had it set like this for years and never had any problems.

        Comment

        • mazzy89
          Automated Home Jr Member
          • Nov 2020
          • 44

          #5
          Thanks for replying here. Which is the differential you set it up?

          Comment

          • GreenGuy
            Automated Home Jr Member
            • Jun 2018
            • 26

            #6
            I have a 300 litre unvented water tank. Heated primarily from an air source heat pump but later we intend to install solar PV with excess power heating the tank via the immersion heater. The reason for the large tank is to enable hot water to routinely be stored at the lowest usable temperature a...


            This link suggests 55c
            Legionella Testing For Domestic Water Systems | Showers are the main source of Legionella dispersal in domestic water systems.



            On Page 10 5.0 A case for Stored Water........ states 5) The need to heat the stored water to 60OC for 1 hour per day to meet legionella regulations.

            Needs expert analysis/report
            Last edited by GreenGuy; 10 November 2021, 04:07 PM.

            Comment

            • MajorDanby
              Automated Home Jr Member
              • Jan 2019
              • 44

              #7
              Stratification occurs in a hot water cylinder by design. Stick it to 60 deg c and you will be fine

              Comment

              • DBMandrake
                Automated Home Legend
                • Sep 2014
                • 2361

                #8
                Originally posted by mazzy89 View Post
                Yes, thank you GreenGuy for the link. I have found it before too ;-)

                However, this does not reply to my question. the rules says the temperature must always be over 60C.

                It means that the heater must be continuously turned on because it is physically impossible to keep the water there inside w/ a temperature above 60.

                This takes me to my question. Despite these regulations in reality how do you program the schedules of your hot water evohome kit?
                The harsh reality that nobody really wants to admit to is that without installing something like an automatic tempering valve (which is typically best done on each hot water outlet) there is no one hot water cylinder temperature which will protect you 100% from the possibility of Legionella and avoid risk of scalding due to excessively high temperatures at the tap, as the two temperature ranges are in direct conflict:

                The maintenance of a water system in a clean state is an important part of managing the risk from legionella.


                "Hot water should be stored at least at 60°C and distributed so that it reaches a temperature of 50°C (55°C in healthcare premises) within one minute at the outlets."

                and yet further down the same page:

                "There is a risk of scalding where water comes out of taps at temperatures above 44°C. In certain facilities eg care homes, this is especially so for whole-body immersion in baths and showers of vulnerable patients, the very young, elderly people, and people with disabilities or those with sensory loss who may not be able to recognise high temperatures and respond quickly.

                You have a legal duty to assess the risk of scalding and to adopt appropriate measures to control it. Your approach will depend on the needs and capabilities of patients or residents. For most people, the scalding risk is minimal where water is delivered up to 50°C at hand-wash basins and a hot water warning notice may be sufficient. However, where vulnerable people can get access to baths or showers and the scalding risk is considered significant, the fitting of thermostatic mixing valve (TMV) Type 3 is required to prevent water being discharged at more than 44°C."

                We have our cylinder set to 54C in Evohome with a smaller than default 5 degree differential - this is the hottest we can set it without the temperature at the hot tap (which is probably around 50C after heat loss through pipes) being excessively hot. It's not quite high enough to guarantee no Legionella, but if it was the much greater risk of scalds and burns would be a reality as we have a small child.

                As we only have 3 hot taps I came very close to installing tempering valves on each tap but two of them were going to be extremely difficult from a plumbing perspective so I eventually abandoned it but I may revisit it in the future. On the other hand our next boiler is likely to be a combi so that avoids the whole hot water storage issue.
                Last edited by DBMandrake; 11 November 2021, 10:12 AM.

                Comment

                • mtmcgavock
                  Automated Home Legend
                  • Mar 2017
                  • 507

                  #9
                  On a sealed system such as a Pressurised cylinder it's very unlikely to get Legionella, also the water would have to be heated constantly and not drawn off for long periods of time such as weeks before it become an issue, that's my opinion anyway.

                  Comment

                  • G4RHL
                    Automated Home Legend
                    • Jan 2015
                    • 1580

                    #10
                    Originally posted by mtmcgavock View Post
                    On a sealed system such as a Pressurised cylinder it's very unlikely to get Legionella, also the water would have to be heated constantly and not drawn off for long periods of time such as weeks before it become an issue, that's my opinion anyway.
                    Legionella develops in pipes where water has been standing some time. It can collect in pipe bends. If a system is regularly used then generally speaking there is not a problem. 60c is the recommended temperature to kill the bug. Temperatures down to 50c can, but take longer. The usual advice to people staying in hotels is to run the shower at maximum temperature for a couple of minutes to flush the system with hot water in case the room has not been used for a little while. Also, don’t stand near the shower whilst it happens to avoid inhaling any droplets. It all sounds worse than it really is but advance thought helps. At home there should not be an issue if the system is used regularly.

                    A combi boiler that provides instant hot water should not be a problem. Just remember that if you have been away on holiday run the water for a short while when you get back to play safe.

                    Comment

                    • MJNewton
                      Automated Home Jr Member
                      • Jan 2021
                      • 21

                      #11
                      Originally posted by mtmcgavock View Post
                      On a sealed system such as a Pressurised cylinder it's very unlikely to get Legionella, also the water would have to be heated constantly and not drawn off for long periods of time such as weeks before it become an issue, that's my opinion anyway.
                      I am inclined to agree. It seems to be far more likely that you'd catch it from someone in the queue in Sainsbury's after they've come back from a holiday in Spain.

                      Of the few hundred cases of legionnaires disease identified in the UK each year, resulting in around 20 deaths, I haven't found a single one yet that has been traced back to a domestic hot water system. I stand to be corrected (for my own protection as well as interest!) if my Google-fu is lacking though.

                      Comment

                      • G4RHL
                        Automated Home Legend
                        • Jan 2015
                        • 1580

                        #12
                        Originally posted by MJNewton View Post
                        I am inclined to agree. It seems to be far more likely that you'd catch it from someone in the queue in Sainsbury's after they've come back from a holiday in Spain.

                        Of the few hundred cases of legionnaires disease identified in the UK each year, resulting in around 20 deaths, I haven't found a single one yet that has been traced back to a domestic hot water system. I stand to be corrected (for my own protection as well as interest!) if my Google-fu is lacking though.
                        Sounds right to me. Legionnaires disease develops in standing water that is left standing for some time, killed if you run hot water through the system at 60c. Hot tubs are good to produce it and you breathe it in through the microscopic water droplets. But then not if it has been regularly used and kept clean. There are other bacteria you can still get from such. I understand a survey done in the USA a few years back revealed that over 95% of the bacteria emanating from hot tubs and jacuzzis was of faecal origin!

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