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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    What's the view here on domestic hot water temperature?

    My thinking is that the incoming water has to be assumed to be safe (and you're mixing that into your hot water to shower so just as much risk from that as from hot if not). 50C enough to stop risk from hot water being any different to cold. 55C should be enough to ensure anything in your tank is killed during a 24 hour cycle.

    * 70 to 80 °C (158 to 176 °F): Disinfection range
    * At 66 °C (151 °F): Legionellae die within 2 minutes
    * At 60 °C (140 °F): Legionellae die within 32 minutes
    * At 55 °C (131 °F): Legionellae die within 5 to 6 hours
    * Above 50 °C (122 °F): They can survive but do not multiply
    • CommentAuthortony
    • CommentTimeJan 9th 2020
     
    at 50C 24/7 sterile

    Canada and USA generally store at 50C

    ( I have been running HW at 50C all my adult life)
  2.  
    My DHW is set at 47c

    Haven't died yet
    • CommentAuthorSimon Still
    • CommentTimeJan 9th 2020 edited
     
    Posted By: tonyat 50C 24/7 sterile

    Canada and USA generally store at 50C

    ( I have been running HW at 50C all my adult life)


    Though this https://www.treehugger.com/green-food/is-it-safe-to-turn-down-your-water-heater-temperature.html suggests public health bodies in both Canada and USA say 60C.

    Posted By: VictorianecoHaven't died yet

    nor have I keeping mine at 46C. You can play Russian roulette for a while without killing yourself but it doesn't mean it's sensible.
  3.  
    Our hot water is the mains tap water passed through a heat exchange on the thermal store, so we have zero legionellae risk. We also can drink water from the hot tap, which is nice when brushing our sensitive teeth and the water pressure in the shower is fantastic.
  4.  
    Out of interest, do you find that water is warm enough for washing up pots and pans?

    AIUI, the risk of legionella depends on quite a few different risk factors, such as whether you are an older person, your general health/unwellness, whether you are often exposed to contaminated water droplets that are very fine so can be inhaled, etc etc. Keeping the water at sterile temperature is an easy catch-all recommendation for everyone. Shh, not a doctor.

    Obviously, standing losses can be reduced even further by not storing any warm water at all - combi boiler or instantaneous water heaters much cheaper than water tanks; or electric showers and point-of-use heaters that also reduce pipe losses; wash hands in cold water if you're that way inclined, or those phase change gadgets if you've enough funds!
    •  
      CommentAuthordjh
    • CommentTimeJan 9th 2020
     
    Posted By: Simon Stillthe incoming water has to be assumed to be safe

    Supposedly mains water is guaranteed that way and the chlorine levels are set so that they have decayed to just above zero by the time the water reaches you. If I run the cold tap for 30 seconds or so, I can just about smell it.

    The bugs breed in stagnant water, either stored in a tank or in pipework that isn't used for a while, especially 'dead legs'. I also suspect that you can acquire some immunity to bugs in your own house over time. So always run a strange shower before using it.

    Posted By: WillInAberdeenOut of interest, do you find that water is warm enough for washing up pots and pans?

    I'd be surprised if most people washing up by hand use water hotter than 40-45°C or so. The main thing when washing grease/fat/oil is to use enough detergent, and the main point in general is to soak things first to loosen dirt.

    Legionella need to get into your lungs to contract the disease. Either by breathing them in or by aspiration (taking into the lungs whilst choking). Oh and legionella aren't the only bugs that breed in water. There are lots more and some of them will survive higher temperatures than legionella. Some can infect via the gut rather than the lungs as well. https://en.wikipedia.org/wiki/Waterborne_diseases

    What I have never understood is how cats, dogs and other animals seem to survive quite happily on any old water whilst we are so precious about clean water. Mind you, one of our cats prefers water straight from the tap. At least neither of them go for the toilet bowl!
    • CommentAuthorArtiglio
    • CommentTimeJan 9th 2020
     
    Legionella was never considered an issue in the domestic environment ( there has been no positive case found in a domestic property that was statistically important ie, above the background level in the population). There used to be a 300l volume exemption, specifically to take domestic systems out of the legislation, as a result of “mission creep” and no doubt the need to be seen to making things ever safer this 300l exemption was removed.
    A classic case of a solution seeking problem.
  5.  
    Posted By: djhWhat I have never understood is how cats, dogs and other animals seem to survive quite happily on any old water whilst we are so precious about clean water. Mind you, one of our cats prefers water straight from the tap. At least neither of them go for the toilet bowl!


    That has puzzled me as well. Cats are supposedly fond of running water - a friend taught her cat to use the toilet (Jazz musician Charles Mingus wrote a guide on how to do this....) and her cat learnt to turn on the bathroom sink taps to drink (which was bit of a problem as the cat of course didn't learn to turn them off)
  6.  
    Posted By: ArtiglioLegionella was never considered an issue in the domestic environment ( there has been no positive case found in a domestic property that was statistically important ie, above the background level in the population).


    That's the info I was looking for. I'll turn mine back down to 50C...
    • CommentAuthorMikel
    • CommentTimeJan 9th 2020
     
    @Simon Still: worth a read
    FOI request for information on legionella in Scotland.
    https://www.whatdotheyknow.com/request/135812/response/335799/attach/3/FOI%20480737%20response.doc?cookie_passthrough=1

    In particular, note the part of this on incidences related to domestic hot water systems.

    We have a solar thermal hot system feeding a 305L unvented hot water tank. Also feeding this is a GSHP heating hot water to 50C and an Immersion heater. The recommendation is that the hot water is heated to 60C once a week. I can find no scientific evidence to back up this recommendation, so it can be taken as a precautionary measure. In practice, we run the Immersion heater about 15-16 times a year, from late October to about mid-February.

    Perhaps you should check your hot water plumbing for any parts where stagnant water might accumulate. Also, little used plumbing should be well flushed, e.g. we have a second bathroom with a shower which is little used. I always let it run for some time before use.
    • CommentAuthorArtiglio
    • CommentTimeJan 10th 2020
     
    <blockquote><cite>Posted By: Simon Still</cite><blockquote><cite>Posted By: Artiglio</cite>Legionella was never considered an issue in the domestic environment ( there has been no positive case found in a domestic property that was statistically important ie, above the background level in the population).</blockquote>

    That's the info I was looking for. I'll turn mine back down to 50C...</blockquote>

    I’m a landlord, all my systems bar 1 are combi’s and plastic pipework, when assessed the greatest risk is from scale build up on taps ( east kent hard water) , tenats get an advice note, which basically says clean your taps, flush through all outlets if you’ve been away for more than a week. But its just beaurocratic meddling. Innthe social housing sector its yet another piece of legislation thats farmed out to contractors that will risk assess to the nth degree , remedial works and ongoing assessments nationally will cost tens of millions every year, all money that could go into actually providing housing, its all plain mad.
  7.  
    Posted By: Artigliowhen assessed the greatest risk is from scale build up on taps ( east kent hard water


    Whats' the risk from build up of scale?
    • CommentAuthorCliff Pope
    • CommentTimeJan 12th 2020
     
    <blockquote><cite>Posted By: Simon Still</cite>Cats are supposedly fond of running water - a friend taught her cat to use the toilet</blockquote>

    Do you mean "use" or to drink from?
    Cats usually distain clean water, preferring water from pans put to soak. Our kittens prefer hanging precariously down the loo to drink the water.

    A conventional hot water tank is fed cold water at the bottom, and as it heats the hottest water rises to the top.
    We have a remote thermometer in the kitchen, the sensor half-way up the tank. Experience shows that 50 degrees C minimum is necessary to produce enough hot water for two baths. Lying in the bath too long periodically topping up the hot water, the hot tap gradually cools, until it runs cool and then chilly.

    I have read that one way round this is to have a pump that constantly recirculates the water around the tank from top to bottom, so then the thermometer gives a correct reading of all the water.
    Otherwise, the temperature is only an average - to get the bottom water hot enough for a bath requires the stove to be run until the top water is nearly boiling.
    •  
      CommentAuthordjh
    • CommentTimeJan 12th 2020
     
    Posted By: Cliff Popepreferring water from pans put to soak

    One of ours has a particular preference for water-filled pea & ham soup cans. Or lentil & bacon. :bigsmile:
  8.  
    Posted By: Cliff PopeDo you mean "use" or to drink from?


    Use. http://mingusmingusmingus.com/mingus/cat-traning-program
    • CommentAuthorborpin
    • CommentTimeJan 13th 2020
     
    The key thing here is whether the tank is storing the water that is dispensed (direct - usually older houses) or if the water dispensed, is heated on demand via a coil (indirect) or combi boiler.

    Indirect is inherently safer as water is not stored at a temperature where Legionella can develop. And only heated a short while before use. It also rarely 'sits' and is not subject to repeated heating cooling cycles.

    The caveat to that is dead legs of pipework which could allow legionella to develop.
    • CommentAuthorArtiglio
    • CommentTimeJan 13th 2020
     
    <blockquote><cite>Posted By: Simon Still</cite><blockquote><cite>Posted By: Artiglio</cite>when assessed the greatest risk is from scale build up on taps ( east kent hard water</blockquote>

    Whats' the risk from build up of scale?</blockquote>

    Its suggested that build of lime scale gives an environment that is more favourable to legionella IF temperatures also favour its growth. Where as in reality old tanks in the area have untold kilos of scale in them and its never been a problem to local health, so just another risk factor introduced to “generate work”, i’ve even seen risk assessments that have labelled hot water cylinders as being a possible risk as there is no access hatch to inspect the interior, how many people have seen a domestic cylinder with an access hatch? and does that mean the system would be drained down to inspect internally if there was one.
    To my mind and having spent a bit of time searching the web, the extension of legionella to individual domestic properties is pure beaurocratic mission creep lunacy, that incurs considerable cost for little if any benefit.
    • CommentAuthorgoodevans
    • CommentTimeJan 15th 2020
     
    It is also worth considering that the weekly disinfection cycle that heat pump systems recommend has the effect of disinfecting only a bit of the system - the bit at the top of the cylinder - it leaves the incoming and outgoing pipes alone and it leaves the bottom of the tank alone. For a pressurised system the bugs have to be supplied by the chlorinated water or pre-installation.
    • CommentAuthorTimSmall
    • CommentTimeJan 15th 2020
     
    Posted By: goodevansIt is also worth considering that the weekly disinfection cycle that heat pump systems recommend has the effect of disinfecting only a bit of the system - the bit at the top of the cylinder - it leaves the incoming and outgoing pipes alone and it leaves the bottom of the tank alone.


    I have seen de-stratification pumps fitted because of this. Generally best to use thermal stores with low heat storage I think (e.g. solar / heat pumps), and I've done this in the past. Currently I only have a combi, and this is usually set to 42C.

    One of the many things on my TODO list is a couple of Bluetooth enabled micro controllers - one to sit underneath the bath, and detect when you've been sitting in the bath for a while, and have turned on the hot tap, the other to tell the boiler to temporarily change the DHW set point to 60C. One day... :-). Until then it's a manual task...
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