Probably not cost effective to replace large hot water cylinder? Or remove?

coffeehound

Shedman said:

coffeehound said:

A good thing about a larger DHW cylinder is that you can heat it to a lower temperature while still getting enough hot water for your needs.  This benefits in a few ways: it loses less temperature during the day; the boiler runs more economically as it's in the condensing mode more; and it lessens the chance of scalds and burns.

As a note of caution, the advice is that Hot water cylinders should be heated to 60°C  to kill off bacteria, especially Legionella, so need to be careful that temp is not set too low.

The 60º figure is appropriate for short sterilisation cycles as it kills any legionella quickly.  But for longer term storage of several hours, any temperature above 51 will sterilise and remain sterile.   I'd think that unvented systems will be a lot less vulnerable than the old unvented systems with a stagnant tank in the loft, too.  But I get that it's best to include a safety margin for inaccurate thermostats etc, so perhaps that's why the 60º number is most recommended.  With a large tank, think I'd use an accurate thermometer and aim for 53º coming out of the furthest tap.

Gerry1

coffeehound said:

But for longer term storage of several hours, any temperature above 51 will sterilise and remain sterile.

Hope you don't end up legless: the unfortunate bloke in NZ had set it to 52.

coffeehound

Gerry1 said:

coffeehound said:

But for longer term storage of several hours, any temperature above 51 will sterilise and remain sterile.

Hope you don't end up legless: the unfortunate bloke in NZ had set it to 52.

Sounds like that could be an inaccurate thermostat then, as they mention.  That's why it's best to not trust the t-stat and instead verify the temperature from the taps.  Another approach would be to run a top-up to 60 with the immersion heater once a fortnight per HSE rules.  

nottsphil

[Deleted User] said:

Shedman said:

coffeehound said:

A good thing about a larger DHW cylinder is that you can heat it to a lower temperature while still getting enough hot water for your needs.  This benefits in a few ways: it loses less temperature during the day; the boiler runs more economically as it's in the condensing mode more; and it lessens the chance of scalds and burns.

As a note of caution, the advice is that Hot water cylinders should be heated to 60°C  to kill off bacteria, especially Legionella, so need to be careful that temp is not set too low.

https://www.stuff.co.nz/national/health/70285141/legionnaires-disease-from-hot-water-cylinder-results-in-amputations

The OP only asked about changing her large hot water cylinder for a smaller one to free up more space in the airing cupboard -presumably to air more clothes - and she ends up getting advice on cylinder lagging; solar diversion and Legionella.

Ever wondered what happens to  the massive excess solar PV generated on sunny spring and summer days for those with a combi? 

nottsphil

coffeehound said:

Shedman said:

coffeehound said:

A good thing about a larger DHW cylinder is that you can heat it to a lower temperature while still getting enough hot water for your needs.  This benefits in a few ways: it loses less temperature during the day; the boiler runs more economically as it's in the condensing mode more; and it lessens the chance of scalds and burns.

As a note of caution, the advice is that Hot water cylinders should be heated to 60°C  to kill off bacteria, especially Legionella, so need to be careful that temp is not set too low.

   I'd think that unvented systems will be a lot less vulnerable than the old unvented systems with a stagnant tank in the loft, too.  

Although covered, they were still vented. I don't see a problem if  the hot water is used regularly, although when I eventually got round to cleaning mine out (after 12 years) there was a disgusting film of slime covering all the underwater surfaces. It was quite labourious  to clean, too.

coffeehound

nottsphil said:
Although covered, they were still vented. I don't see a problem if  the hot water is used regularly, although when I eventually got round to cleaning mine out (after 12 years) there was a disgusting film of slime covering all the underwater surfaces. It was quite labourious  to clean, too.

Yes with vented tanks it's too uncertain whether the turnover will be high enough to prevent growth as the chlorine evaporates.  Whereas water in unvented systems stays chlorinated throughout so must be safer.  There might still be 'dead legs' in pipework where stagnant water could collect I suppose..