What temperature should my hot water be set at?

[Mike_scotland]

Hi group,

 

I have a Grant ashp that heats my water for the 300l cylinder, what temperature should the cylinder be? 

 

I was hearing something about a 1nc a week purge to 60 degrees or something? 

 

Thanks,

 

Mike

[Temp]

What sort of cylinder?

 

All cylinders use some sort of coil (or heat exchanger) to separate the water in the primary (ashp/boiler) from the secondary side (taps and showers etc). This heat exchanger can either be on the input side or output side of the tank. 

 

If its on the input side then the 300L of water in the tank cant be dosed with biocide because its the same water that comes out of the taps. In this case its recommended you heat the cylinder say once a week to 60C to kill off bugs such as legionnaires disease.

 

If its on the output side then the 300L of water in the tank is the same water that circulates around the ashp/boiler circuit and this can normally be dosed up with corrosion inhibitor and biocide. The secondary side (Incoming main -> heat exchanger -> taps) is short/low volume that is regularly flushed with new water from the mains. I suspect this makes it much less likely to grow bugs. 

 

 

[JohnMo]

Although mains water is dosed with chlorine, so unless you have opened the line for repair or maintenance, there should be no bugs to grow.

[Conor]

If it's an invented system, there's no need to heat to kill. 

[tonyshouse]

Nearly all of North America and Canada set at 50C, I have been keeping mine at 50C most of my life 

 

lower the better as less heat loss, you don’t want extra heat in the house if we get a summer. 

[Redoctober]

@Mike_scotland we have our set at 55oc and is plenty hot enough. Probably too hot at times as the nearest tap to the cylinder, produces very hot water immediately and has to be mixed with some cold to be comfortable.

[joe90]

I set mine to 48’. Very adequate.

[ProDave]

Another one at 48 degrees here.  Found by trial and error to be the hottest I can just about hold my hands under if I draw if sink of washing up water just from the hot top.  I don't see any point in having it hotter.

 

Treated mains water into an unvented cylinder has no opportunity to get bugs in so a weekly cycle to heat it hotter is pointless.  You only need that if it's not mains water or it's a vented tank.

[Mike_scotland]

Hi guys,  thanks,

 

Im pretty sure im unvented but my heat pump guy said purge once a week with immersion? 

[tonyshouse]

It is called belt and braces, the evidence is there for not needing to do this, North America and I did see a paper that referenced constant 50 C doing sufficient sterilisation against Legionella. 

[Radian]

19 hours ago, Mike_scotland said:

I was hearing something about a 1nc a week purge to 60 degrees or something? 

 

Do you have any Solar PV?

[Mike_scotland]

20 hours ago, Radian said:

Do you have any Solar PV?

Not yet, in the pipeline to get it this year bud

[SteamyTea]

Bit bored this morning, so thought I would look up about domestic legionella infection risk.

 

First line 'very uncommon'

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/635817/Investigating_Legionella_household_settings.pdf

 

Seems your hosepipe is a risk as well.

As is the screenwasher on your car.

https://www.sciencedaily.com/releases/2014/05/140518164421.htm

 

Here are the numbers for the UK.

https://www.gov.uk/government/news/latest-legionnaires-disease-data-published-for-england-and-wales

 

 

Edited May 9, 2022 by SteamyTea

[JohnMo]

That's interesting, no mention of hot water storage (or did I miss it). Somewhat shows the pasteurisation cycle of 60 degC is not a thing of concern in the UK.  Otherwise it would get a mention.

 

But the main issue for most households is with infrequently used outlets, we have a couple, and so will plenty of other people.

[SteamyTea]

Just now, JohnMo said:

But the main issue for most households is with infrequently used outlets, we have a couple, and so will plenty of other people.

Seem the main concern should be going to Thailand.

 

With around 300 cases a year, and very few fatalities, it is getting to such low levels, we should be worried about putting the phone charger in a socket.

 

Things have to be kept in perspective, being at work is much more dangerous.

Key figures for Great Britain (2020/21)

• 1.7 million working people suffering from a work-related illness, of which
  • 822,000 workers suffering work-related stress, depression or anxiety
  • 470,000 workers suffering from a work-related musculoskeletal disorder
  • 93,000 workers suffering from COVID-19 which they believe may have been from exposure to coronavirus at work
• 2,369 mesothelioma deaths due to past asbestos exposures (2019)
• 142 workers killed at work
• 441,000 working people sustained an injury at work according to the Labour Force Survey
• 51,211 injuries to employees reported under RIDDOR

[Radian]

3 hours ago, Mike_scotland said:

Not yet, in the pipeline to get it this year bud

You can get a device that routes excess PV generation into an immersion heater. This can then be set to higher temperature to do the sterilisation.

 

[Mike_scotland]

Thanks guys! as always its all good points your making!  

[Radian]

Just resuscitating this topic because I'm trying to increase the efficiency of my condensing boiler and while the radiator sizing for space heating is such that I can just about operate with a flow temperature of 60^oC the hot water can't reach 55^oC as I currently have it set. Because of the limitations of the boiler in question I have to work with just a single fixed flow temperature.

 

Ideally I'd like to set the HW to 47^oC which experimentation shows is all that's needed for washing and has the benefit of protecting from scalds (as others have discussed here) and can be achieved with a flow of 60^oC. I have taken on board the opinions that legionella is not a real concern but I am, by nature, risk averse. However, when I think about it logically there's plenty of places where water accumulates at lower temperatures. For starters, all the pipework between taps and cylinder would need purging to ensure there was no contact with water left at lower temperatures. And then there are those occasional events where the tank is not timed to be used yet water is still drawn off, or when all the HW has been used yet more is demanded for an ultimately disappointing shower.

 

But even more confusing is the cold water! Again, this is talking with respect to taps supplied by a vented storage tank situated in a loft. It's always been my understanding that you don't drink from such sources and neither would I want to given the appearance of a typical tank after accumulating decades of crud. But this water routinely ends up in showers and baths, on hands and faces, etc. Is it supposed to be too cold for harmful bacteria? At 20^oC it is around 18^oC away from body temperature so about the same margin as the recommended HW temperature (I understand that it's keeping the operating zones between humans and bacteria sufficiently separate that makes things safe rather than killing bacteria) but in hot weather the cold water storage tank can reach much higher temperatures - i.e. I measured water coming out of 'cold' taps at over 26^oC last month.

 

It therefore seems to me as though the official advice of keeping water above 55^oC has to be flawed because of all the exceptions I've been listing here.

[markc]

Cold water taps should not be supplied from a tank. The tank should be fed from cold water and is there to keep a boiler and cylinder full.

as for temp of water, I have found my boiler works best, shower heats up quickly and my bills appeared to reduce when I upped the water temp to 70.

I love my showers, at least one every day, sometimes 2 but not home everyday so let’s say 30 per month. No heating on at moment and last month my gas was £12 so showers costing me 40p each.

sorry, correction … £12.53 for the month

Edited September 9, 2022 by markc

[Radian]

28 minutes ago, markc said:

Cold water taps should not be supplied from a tank.

 

I don't know how familiar you are with gravity fed domestic water systems but vented HW cylinders tend to be paired with bathroom cold taps of the mixing variety fed from the same gravity source otherwise the differential pressure can be a problem. Every house I've ever been in with gravity fed water systems have had cold taps fed from the storage tanks on the top floor, which has been standard practice up until the advent of UVC's. It might be said that cold water taps would be better if fed from the main when a UVC is used but this would nearly always be the case anyway.

 

41 minutes ago, markc said:

I have found my boiler works best, shower heats up quickly and my bills appeared to reduce when I upped the water temp to 70.

Presuming it's a condensing boiler then it's certainly not working efficiently. At 54°C return flow, under perfect testing conditions, the boiler is only up to 87% efficient. In practice it will be significantly less.

 

 

[Temp]

2 hours ago, Radian said:

Just resuscitating this topic because I'm trying to increase the efficiency of my condensing boiler and while the radiator sizing for space heating is such that I can just about operate with a flow temperature of 60^oC the hot water can't reach 55^oC as I currently have it set. Because of the limitations of the boiler in question I have to work with just a single fixed flow temperature.

 

Ideally I'd like to set the HW to 47^oC which experimentation shows is all that's needed for washing and has the benefit of protecting from scalds (as others have discussed here) and can be achieved with a flow of 60^oC

 

From the USA  (yes I know their systems are different)..

 

https://pubmed.ncbi.nlm.nih.gov/31940510/

 

Quote

 

Legionella spp. and L. pneumophila gene numbers were highest for water heaters set at or below ∼42 °C and significantly decreased >51 °C, consistent with Legionella's preferred temperature range. 

 

 

[Temp]

A lot depends on your attitude to risk.  Official advice in the UK from the HSE says keep stored hot water above 60 and cold water below 20C.

 

 

[SteamyTea]

1 hour ago, Radian said:

Every house I've ever been in with gravity fed water systems have had cold taps fed from the storage tanks on the top floor, which has been standard practice up until the advent of UVC's

My 1987 house wasn't. Had to run a need feed to the pumped shower unit when I fitted it. First time I have ever seen it plumbed in that way mind.

[Radian]

5 minutes ago, SteamyTea said:

My 1987 house wasn't. Had to run a need feed to the pumped shower unit when I fitted it. First time I have ever seen it plumbed in that way mind

Your autocorrect drives me nuts 😆 Do you mean you got a new feed from cold storage tank to make the pressure for H & C the same?

[SteamyTea]

18 minutes ago, Radian said:

Your autocorrect drives me nuts 😆 Do you mean you got a new feed from cold storage tank to make the pressure for H & C the same?

That does not make any sense, what was android thinking.

 

Yes, I ran a new cold water pipe from the loft tank to the shower pump. Then the static pressures were the same. 

Worked well until a friend filled the bath to the brim and emptied the F&E.

She may have been a pigmy, but was no need to make the bath into a swimming pool. Bloody Aussies, they have no idea about the environment.