Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Evohome hot water settings to prevent legionella

  1. #1
    Automated Home Jr Member
    Join Date
    Nov 2020
    Posts
    44

    Default 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?

  2. #2
    Automated Home Jr Member
    Join Date
    Jun 2018
    Posts
    22

  3. #3
    Automated Home Jr Member
    Join Date
    Nov 2020
    Posts
    44

    Default

    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?

  4. #4
    Automated Home Sr Member
    Join Date
    May 2021
    Posts
    89

    Default

    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.

  5. #5
    Automated Home Jr Member
    Join Date
    Nov 2020
    Posts
    44

    Default

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

  6. #6
    Automated Home Jr Member
    Join Date
    Jun 2018
    Posts
    22

    Default

    https://forum.buildhub.org.uk/topic/...nd-legionella/

    This link suggests 55c
    https://hydrosense-legionella.com/le...water-systems/

    https://hotwater.org.uk/uploads/5B053A7597A5F.pdf
    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; 10th November 2021 at 04:07 PM.

  7. #7
    Automated Home Jr Member
    Join Date
    Jan 2019
    Posts
    44

    Default

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

  8. #8
    Automated Home Legend
    Join Date
    Sep 2014
    Location
    Scotland
    Posts
    2,354

    Default

    Quote 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:

    https://www.hse.gov.uk/legionnaires/hot-and-cold.htm

    "Hot water should be stored at least at 60C and distributed so that it reaches a temperature of 50C (55C 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 44C. 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 50C 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 44C."

    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; 11th November 2021 at 10:12 AM.

  9. #9
    Automated Home Ninja
    Join Date
    Mar 2017
    Posts
    497

    Default

    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.

  10. #10
    Automated Home Legend
    Join Date
    Jan 2015
    Location
    NE UK
    Posts
    1,402

    Default

    Quote 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, dont 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.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •