Keeping hot water temperatures down

SusanCarter

Our gas consumption was 0.2 units per day from 3rd May to 3rd Oct this year. This worked out at about £20 which is aproximately 13p/day. During this time gas would also have supplied us for cooking but not for the shower as that is electric.

I presume the legionella thing would not apply to us as we have a combination boiler. I don't know how hot our water is but I think it is probably close to 60 degrees. The main reason we have it so hot is because it is rather temperamental and we would end up with a cold bath if we didn't have it set that high. It is only really used for baths and washing up as anything else is not worth standing about for 3 minutes running a couple of gallons of water down the drain.

I imagine one reason for few cases of legionella would be that so many people have combination boilers. Also, it is only necessary to kill the bacteria if they get in the hot water tank in the first place. I guess usually it doesn't otherwise as you say there would be many more cases.

I may be wrong but I think legionella can be deadly whcih is possibly why we are told to take this precaution. I have never heard of a case of whooping cough, diptheria or tetanus and have only heard of one case of polio in people I have known but we still take the precaution of vaccination (although obviously the environmental impact of vaccination may be different).

When I was a child a local swimming baths had legionella in their showers (although I don't know any details as I was only nine at the time) so for ages there were only cold (and I mean COLD!) showers. More recently our local news reported some strain of legionella being caught by a few people at some health/fitness club which had a swimming pool. I think the health club may have been closed for a while because of it.

I think if you only have the water heating on for a short time there is a much lower risk than if you have it on constantly as somewhere like a swimming baths with greater demand for hot water would.

Ken68

Hi George......Well, that knocks on the head my experiments this summer with sun heated water.
That means that solar powered water panels should only be connected to hot water cylinders that are regulated at 60 degrees additionally if needed from another source.!!!
Very little mention of this critical law in the research that I've done.Ye gods.

George_Bray

Ken68 wrote:

Hi George......Well, that knocks on the head my experiments this summer with sun heated water...

I fear you may be correct. It appears there's some risk with any 'pool' of water sitting at much less than 60C, whether it be a large tank, spa, Jacuzzi, small shower head, thermostatic valve or little-used pipework. I'm shocked to realise this. Is chlorine really so ineffective?

I had no idea before this morning. I will keep heating my water to 40C once a day but (as right now for the first time) to 60C or 70C for a few hours once a week in an attempt to keep the bug level low. I will also soak my shower head in bleach and advise everyone else to do the same! The water at anyone's shower head cannot be much above 40C or it would burn you.

I just found the following web page, with some thinking not unlike my own:

http://www.theyellowhouse.org.uk/themes/heatwat.html

They say:

"Turn down the thermostat on the water tank
In most households the thermostat on the water tank is set for an absurdly high temperature- indeed in most households no one even knows where it is! (It’s usually a small box attached to the side of the tank about half way up with a dial with temperature settings). Immediate economies can be achieved by setting the thermostat to the temperature of water that is actually needed rather than heating water up to 75°C and having it sit around all day only to dilute it with cold water when you need it. As a rule of thumb, water is hot enough for a shower at 37°C, a bath at 40°, a washing machine cool wash at 40°, and a dishwasher economy wash at 60°C. Tank thermostats are particularly inaccurate, so the best strategy is probably to turn it down little by little until it gets too cool."

"It is also to worth setting a low tank temperature if you have a condensing boiler because the boiler stops condensing as soon as the return water (which will be the same temperature as the tank) goes over 45°C."

***"Occasionally one is warned that a cooler tank could develop Legionnaires disease. Personally I believe this to be a very low risk given the high turnover of water in a domestic system. To the very best of my knowledge, Legionnaires disease has never developed in a solar hot water system which typically has a tank temperature between 40 and 50 degrees C."***



More on my actual costs and other questions later...

Regards
George

SusanCarter

George_Bray wrote:

I fear you may be correct. It appears there's some risk with any 'pool' of water sitting at much less than 60C, whether it be a large tank, spa, Jacuzzi, small shower head, thermostatic valve or little-used pipework. I'm shocked to realise this. Is chlorine really so ineffective?

Presumably the amount of chlorine they put in is not enough to kill everything. (Or perhaps it only kills certain bacteria?) Or maybe the recommendations are over cautious. Incidentally, swimming pool water is usually around 30 degrees and they put lots of chlorine in it (relative to domestic water supply) which is presumably to kill the bugs. Of course, there would naturally be a lot more bugs introduced into a swimming pool due to all the people swimming about in it.
EDIT: Perhaps historically our domestic water supply was not as clean as it is now so the risk used to higher but the advice has not changed.

gromituk

Leginnaire's disease is a relatively recent phenomenon. I doubt that water quality has improved generally since it was discovered.

George_Bray

Susan

>Presumably the amount of chlorine they put in is
>not enough to kill everything.

Good point. I'm now wondering if one can buy/improvise a chlorine 'injection' system to raise the chlorine level in domestic hot water a bit (but not what you drink). I say "improvise", because if nothing is made/sold for this purpose, then one should be able to use whatever is sold for residential swimming pools. It would only make sense, though, if the active ingredient is quite cheap. Otherwise, I will stick to my idea of 20-40C for 6 days a week, increased to 66C for 1 day a week. I left my boiler on maximum overnight and it got up to only 66C! So my system can't be very efficient.

>Perhaps historically our domestic water supply was
>not as clean as it is now so the risk used to be higher
>but the advice has not changed.

To the contrary, they seem to have tightened up on the advice because it only used to apply to water tanks over 300 litres - now it applies to all water tanks, apparently.

GromitUK

>Leginnaire's disease is a relatively recent phenomenon.
>I doubt that water quality has improved generally
>since it was discovered.

It was only discovered in the 1970s but I believe it's probably always been around and, before the discovery, they assumed fatalaties were from some other cause so it's not "a relatively recent phenomenon".

I just found:

http://www.swimmingpoolchemicals.co.uk/product_info.php?products_id=77

A 5Kg tub of Sodium Dichloroisocyanurate granules = 5000g costs £13

They suggest adding 100g per 50 cubic metres of water (1 ppm), for a swimming pool.

I use only about 25 cubic metres of water for a whole year's worth of showers.
So I'd need only 50g of granules per year, which would cost only 13p per year!

Or be super-cautious and increase the chlorine to 2 ppm as recommended for a spa. That would cost only 26p per year but, say, £1 a year to cover all the tank water used in the whole house. The challenge may be to find a dosing system which would slowly drip a partly dilute solution into the cold water tank at the target concentration.

Ultimately, though, who knows if additional chlorine kills the L bacteria and if it would make clothes smell funny when they come out of the washing machine?

Regards
George

SusanCarter

George_Bray wrote:

Ultimately, though, who knows if additional chlorine kills the L bacteria and if it would make clothes smell funny when they come out of the washing machine?

You'd probably get used to the smell. I used to do a lot of swimming and it really affected my sense of smell for chlorine. One time as a student I was mistakenly doing an experiment on the bench which should have been in a fume cupboard. My friends noticed because the smell of chlorine was so strong but I hadn't noticed the smell at all.

SusanCarter

George_Bray wrote:

Ultimately, though, who knows if additional chlorine kills the L bacteria and if it would make clothes smell funny when they come out of the washing machine?

You'd probably get used to the smell. I used to do a lot of swimming and it really affected my sense of smell for chlorine. One time as a student I was mistakenly doing an experiment on the bench which should have been in a fume cupboard. My friends noticed because the smell of chlorine was so strong but I hadn't noticed the smell at all.

gromituk

George_Bray wrote:

It was only discovered in the 1970s but I believe it's probably always been around and, before the discovery, they assumed fatalaties were from some other cause so it's not "a relatively recent phenomenon".

Yes, but that's not my point: I was responding to the suggestion that advice on its treatment may be out of date because water quality has increased over the time that the advice has been around. I don't think it's increased significantly since the 1970s.

I could imagine that adding chlorine to your water in order that you don't have to use minimal amounts of fuel to heat it to 60 degrees instead of 40 degres would likely have a net negative impact on the environment.

Phil_L_2

The bacterium that causes Legionnaire’s disease is endemic in the environment and it is generally found in the domestic water supply every third day. It breeds best at 37°C but becomes dormant at 50°C and dies at 57°C. The recommendation for hot water systems is to store the water at 60°C and blend the hot and cold at the outlets to no more than 43°C, which is scalding temperature.

In terms of risk to health it becomes dangerous when it becomes an aerosol (fine mist), which is breathed in and is most dangerous to older people. If I remember correctly there are slightly less than 300 deaths per annum in the UK from legionellosis of which 50% are contracted abroad.

On the bright side as an organism it does not compete very well and requires standing water to breed. A high turnover of water, dirty tanks and a lack of iron fittings makes most domestic installations a low risk. Paradoxically commercial systems that are better looked after are better breeding grounds and schools with their six-week summer break can be a significant risk. The reason that there have been no reports of outbreaks from domestic properties is due to the fact that the risk area is the shower that is generally confined to the bathroom and only kills one person at a time.

I would not suggest using chlorine injection since this is very expensive for little gain. For the particularly paranoid an ultra violet disinfection unit is probably the best solution.

If you are really interested follow this link http://www.bsria.co.uk/press/?press=93
I hope this clears up a few things.