Keeping hot water temperatures down

George_Bray

I suggest this must be one of the best ways of saving energy at home. I've found that water for a really hot shower only needs to be at about 40C, measured at the copper wall of the water cylinder. Mixing hotter water with cold strikes me as a waste. But this 40C is only for a shower...

For washing hands, who needs water at anywhere near 40C? 20C would be more than adequate, in my opinion, just to have taken the chill off the water in winter. Often, by the time the hot water has reached the tap through all the pipes, one has finished anyway, so that's another waste.

I am shocked at the number of respectable, household-name company/organisation washrooms I visit where the wash basin water is too hot to handle. This is such a disgraceful waste. Is there any good reason for the water needing to be so hot? 20C would be more than good enough in all these places, too.

Also, I just found a Government web page on Water Supply (Water Fittings) Regulations, 1999: http://www.defra.gov.uk/environment/water/industry/wsregs99/guide/section8.htm

On hot water distribution temperatures, the regulation at G18.2 says:

"Hot water should be stored at a temperature of not less than 60oC and distributed at a temperature of not less than 55oC. This water distribution temperature may not be achievable where hot water is provided by instantaneous or combination boilers."

Why is this? I would find it impossible to withstand a shower temperature much higher than 40C, so why would anyone want to heat their water to anywhere near 60C?

Regards
George

PS I just read a comment by Matt on another thread that:
"... if you have stored hot water (which you will have with Solar) you will need to raise the temp to 60 degrees C to kill off leigionella."

Well, I've seldom heated my water to anywhere near 60C for decades and I've never caught anything. Is this a serious risk?

cosworth_monkey

Seems like a fair point that....showering at more than 40 degrees??? that would be painful!

How would you go about changing the boiler to heat to 40 degrees instead of 60?

George_Bray

We live and learn. I'm amazed I'd never heard of Legionnaires Disease being a risk factor for domestic hot water systems, which according to a search of Google and numerous USA and other health organisations web pages, it is.

BUT...how come I've never read of any local (or even national) cases of the disease at anyone's home? Have any of you heard of any UK residential cases? I assume it would be BIG news, like cases from Hospitals, etc. I always thought it came just from ventilation air, not from vapourized hot water, like from a shower head, but it seems I'm wrong. Also, I've been heating my water cylinder to just 40C or thereabouts for years, without any health problems which I'm aware of. What's more, the water in the cylinder cools down to about 20C over the next 23 hours before I heat it back up to 40C again.

I would have hoped that the chlorine in the water was adequate for keeping such nasties at bay. Holding water at 60C+ seems a very high price to pay in energy terms, for the avoidance of this disease.

Regards
George

Cardew

George_Bray wrote:

We live and learn. I'm amazed I'd never heard of Legionnaires Disease being a risk factor for domestic hot water systems, which according to a search of Google and numerous USA and other health organisations web pages, it is.

BUT...how come I've never read of any local (or even national) cases of the disease at anyone's home? Have any of you heard of any UK residential cases? I assume it would be BIG news, like cases from Hospitals, etc. I always though it came just from ventilation air, not from vapourized hot water, like from a shower head, but it seems I'm wrong. Also, I've been heating my water cylinder to just 40C or thereabouts for years, without any health problems which I'm aware of. What's more, the water in the cylinder cools down to about 20C over the next 23 hours before I heat it back up to 40C again.

I would have hoped that the chlorine in the water was adequate for keeping such nasties at bay. Holding water at 60C+ seems a very high price to pay in energy terms, for the avoidance of this disease.

Regards
George

George,
I assume the reason why we don't hear of many cases is because the water is heated to 60C.
Also I believe that it takes some time for the 'nasties' to develop; so heating up the water to 60C from time to time will kill off the germs.
Also with a well insulated tank I wonder if the difference between heating water to 40C and 60C will be that great?

Incidentally how do you get your water set as low as 40C?

Also with the growing trend toward Combi boilers(i.e. no tank) this doesn't apply.

George_Bray

Cardew wrote:

Incidentally how do you get your water set as low as 40C?

Cardew and Cosworth

There is a temperature dial on my hot water heater. It's an indirect, circulating system with a 110 litre water tank in the airing cupboard. The boiler control dial has no figures, just a zone shown as 'hot'. Well, I set it below 'hot'. But my main control is to limit each 'burn' to about an hour in winter and 30 minutes in summer. That takes the temperature up from about 20C to 40C. I now read that 20C - 45C is the ideal (i.e. worse) temperature for breeding Legionnaires bacteria, whereas 60C kills them off. I also read that spa baths and whirl pools are considered to be high risk. I'll never again be able to relax under the shower. But am I prepared to more than double/triple my gas bill by keeping the water tank at 60C all the time?

Also, it seems there used to be a 300 litre threshold for tank size, above which the authorities considered the health risk was relevant. Now, they say all tank sizes are at risk. But it seems to me that the risk with my 110 litres tank is still low. I ask again, has anyone ever heard of anyone catching Legionnaires disease from a domestic shower in the UK?

Please see:
http://www.hse.gov.uk/pubns/indg376.pdf

Also, here's a recent UK case of a dirty shower head leading to a man's death but, again, it's at a hospital, not in a private home. Nevertheless, I will dip my shower head in some bleach as a preventive measure.

http://www2.netdoctor.co.uk/news/index.asp?id=123897&D=10&M=8&Y=2006

Regards
George

Cardew

George_Bray wrote:

Cardew and Cosworth

But am I prepared to more than double/triple my gas bill by keeping the water tank at 60C all the time?

George,
How do you calculate that?

Domestic hot water only accounts for a small(ish) proportion of a Gas CH bill - the average is £100-£150pa.

Heat losses from a well insulated tank are very low anyway. I have checked my meter and gone away for a weekend leaving the water switched on(but obviously nothing used; and a cold house) and was surprised at just how little gas had been used after making allowance for the pilot light.

What is your estimate of savings(in kWh) between your method of keeping your water temp low, and the more conventional method of having heating on a timer for an hour in the morning and evening? - set to 60C. Of course if you use water after the heating period you will not be "keeping your water at 60C"

Might be an interesting experiment?

George_Bray

Cardew wrote:

George,
How do you calculate that? Domestic hot water only accounts for a small(ish) proportion of a Gas CH bill - the average is £100-£150pa.

I wrote about this here at MSE last year and nearly got laughed out of the forum. But it's true that I manage to keep gas consumption and total costs very low. I mean to do a check to see how actual use compares to the plan/forecast made last year. Anyway, my gas is used for all water heating, cooking and (warm air) heating. I do a fair amount of cooking, too. I don't eat many chilled foods warmed up in a microwave. From May to October I used an average of 0.2 of a 'meter unit' per day. That's the dial reading on the meter before adjustment for KwH. It goes up a bit in winter but not by very much. I found that the pilot lights are incredibly wasteful so I keep those off. How does 0.2 dial units per day compare with your readings?

Regards
George

gromituk

George_Bray wrote:

I always though [legionella] came just from ventilation air, not from vapourized hot water, like from a shower head

It comes from water vapour, which can be produced by the external cooling systems of some air conditioners (which use sprayed water) or, say, a shower head.

gromituk

George_Bray wrote:

But am I prepared to more than double/triple my gas bill by keeping the water tank at 60C all the time?

I know this has been answered already, but I think it needs clarification: the saving to heat to 40 instead of 60 degrees will be minimal, assuming your tank is well insulated: you will simply use less water at 60 degrees than you would use at 40 degrees.

jellycat40

George, I am a simple person and do not understand the measurement of the gas. What does your monthly, quarterly or annual use of gas cost you and what size house does this relate to.

I live in a detached 4 bedroom, 2 receptions house and I pay £38 per month in gas. I have gas cooker, central heating and hot water.

Thanks Louise

Cardew

George_Bray wrote:

From May to October I used an average of 0.2 of a 'meter unit' per day. That's the dial reading on the meter before adjustment for KwH. It goes up a bit in winter but not by very much. I found that the pilot lights are incredibly wasteful so I keep those off. How does 0.2 dial units per day compare with your readings?

Regards
George

George,
It depends if you have an Imperial meter or a metric meter.

0.2 dial units are approx 2kWh on a metric meter and 6kWh on an Imperial meter.
That means you cook, centrally heat and have hot water using less than 1,000kWh or 3,000kWh per year.

I remember the exchanges last year and it is not worth going over old ground.

To a large extent consumption depends on the size of house and number of people, so comparisons are meaningless. Suffice to say I use many many times your consumption.

However as stated above - for information of other people reading this thread it is not a good idea to keep your water at a low temperature and the savings are minimal if you did.

P.S.
Do you seriously keep of the pilot light and light the boiler manually every time you use it?