Non-motoring > Hot water cylinder stat setting Miscellaneous
Thread Author: smokie Replies: 22

 Hot water cylinder stat setting - smokie
I was reading elsewhere that a household of 2 people using about 4kWh of gas a day for showers and washing up.

My usage is between 10 and 11 every day for the same.

My cylinder and stat are pretty old but my boiler is nearly new.

The stat is set to 60 which is the recommended temp as it prevents legionnaires.

But there is more info suggesting you can get away with 49 degrees.

My stat is mounted quite near the bottom of the tank, so it must be trying to heat the whole tank to 60.

So the questions are

1) what do we think about moving it up the tank a bit or turning it down to 50?

2) is the stat likely to be bust, as the water is too hot to put your hand under (I am going to measure the heat)

Or should I just leave well alone?
 Hot water cylinder stat setting - No FM2R
I wouldn't drop the temperature. I worry about such diseases.

What's the boiler insulation like?

& 4kWh? Not in my house! Ok there's 4 of us, but our usage is a darn sight more than 8kWh and we don't have heating. Though we do cook with it.
 Hot water cylinder stat setting - Bromptonaut
Mines around the 9kwh/day mark based on Jun-July. Bit lower in July-Aug but we were away for a fortnight. That's domestic HW and such stuff as we cook on hob for two - oven is electric.

Conventional boiler (20yo Baxi) with indirect cylinder. Cylinder has integral foam jacket but builders didn't insulate pipes. Short pipe run to shower but takes ages to run warm in kitchen.

I was press ganged into a City and Guilds qualification in energy advice four years ago. Then CEO, who was subsequently defenestrated, needed to say we had 'N' qualified advisers for a funding bid. I can remember the bit about legionnaires, loads about black mould and ventilation/insulation plus how to read any sort of meter but a lot of the rest is forgotten unless I dig out notes.

It will depend on who they get funding from but might be worth seeing if your local Citizens Advice can give you any advice on energy?
Last edited by: Bromptonaut on Wed 11 Sep 19 at 20:41
 Hot water cylinder stat setting - Kevin
>I wouldn't drop the temperature

Neither would I. A few weeks ago there was an article on one of the news sites by a microbiologist who said that legionella thrives in domestic water systems especially if they aren't used for a few days. He runs his taps for 20mins whenever he returns from trips away.

Found it:
Last edited by: Kevin on Wed 11 Sep 19 at 21:16
 Hot water cylinder stat setting - sooty123
Done that far years, no idea if it's a good idea but not got legionella yet.
 Hot water cylinder stat setting - Bromptonaut
>> Found it:

Not clear how that helps if there's legionella in the water - water mist around running taps waiting to be inhaled is exactly what the virus needs to spread.
 Hot water cylinder stat setting - Kevin
If you read the article he says that he covers his nose and mouth, turns on the taps and leaves closing the door. After 20mins he turns them off, closes the door again and waits 20mins for any water vapour to disappear.

I take your point though. If he's so concerned about legionella why doesn't he go the whole hog and wear a mask when he turns the taps on and off.

Still, must be better than taking a shower in it.
Last edited by: Kevin on Wed 11 Sep 19 at 22:39
 Hot water cylinder stat setting - Zero

>> The stat is set to 60 which is the recommended temp as it prevents legionnaires.

And also to prevent furring up. 50 is too cold.

Not too hot tho, if you have a shower pump it will cavitate above 65
 Hot water cylinder stat setting - smokie
OK I'm getting the message!! :-)

My 10 kWh doesn't include cooking or heating (at the moment, though SWMBO "feels the cold" so that's not so far off).

I will faff around seeing what the actual water temp is and maybe shortening the time it's on for, though I can see my half hourly consumption using the API into my suppliers data and it looks about right - any less and it wouldn't reach temperature!!

I'll also look back over the bills prior to the boiler to see if I'm saving but I don't have truly comparable data really. However the difference should, in my mind, be at least 30% less fuel used over a summer month.

The tank is old and has that solid foam covering. A jacket might help reduce loss a bit I suppose.

Just in case anyone apart from me is interested, yesterday looked like this (and totalled almost 13 kWh!!). Sort of proves the on/off times are about right I think. 1st shower was about 9:40 IIRC. Figures in brackets are for 4 Sept when showers were a bit earlier as we went to London for the day, returning after 20:00 - so def no daytime usage.

8:30 9:00 3.332 (3.41)
9:00 9:30 1.233 (3.188)
9:30 10:00 1.659 (1.067)
10:00 10:30 2.35 (0.648)
10:30 11:00 0.441 (0.367)

18:00 18:30 2.71 (2.059)
18:30 19:00 1.00 (0.916)

Interesting that it seemed to be back up to temp by 11:00 but had lost some by 18:00 - that's almost all just cooling loss as I doubt hardly any hot water was run in that time. Sorry if I'm coming across as a sad old geezer with too much time on his hands (for that is what I am :-) )
 Hot water cylinder stat setting - Netsur
Is your hot water cylinder insulated (and well insulated)?

 Hot water cylinder stat setting - Zero
>> Is your hot water cylinder insulated (and well insulated)?
Is it dipped or jacketed?
 Hot water cylinder stat setting - RichardW
4kWh is only enough to run a (barely adequate) 10kW electric shower for 24 minutes. It seems unlikely that this is 'average' useage for 2 if you add in 2 daily showers plus cooking - maybe if you only shower every 3rd day....!

From the numbers you posted, you are using a reasonable chunk at 18:00 when the DHW comes back on - this is making up only the loss on the tank - so if you want to save some of this, get some more insulation on the tank. Even if you only cover it with a old duvet or similar you will find that it will be hot under the Duvet.
 Hot water cylinder stat setting - Kevin
>.. get some more insulation on the tank.

My hot water tank has the dipped foam insulation. Besides keeping the airing cupboard warm it also seems to be used for stopping the cold water tanks directly above it in the loft from freezing. The water tanks are covered with an insulation blanket but there is no insulation underneath them. The rest of the loft has about 300mm of insulation so I guess it might get a bit cold up there in winter.
 Hot water cylinder stat setting - Manatee
We used no heating in August, so only hot water and cooking.

I read the meters in our rented house on 1/8 and 31/8.

In 30 days we used 347kWh of gas, 11.57kWh per day. The boiler is an ancient Potterton Netaheat 10-16 Mk2 F, which as far as I can deduce is 30+ years old. The hot water is hot, but not scalding - tank stat is at 50-55, boiler stat is only numbered 1-5 and has been on about 1.5 all summer. I'll put that up a bit when the heating is on regularly.

Despite its age it is apparently fairly efficient. It uses spark ignition rather than a pilot light and has a fanned flue, and makes a hell of a noise when it fires.
 Hot water cylinder stat setting - sherlock47
>>>tank stat is at 50-55<<<

I suggest that you ask your landlord (or Agent) for a copy of his Legionnaires' risk assessments.

Certainly the stat should be set above 60!
Last edited by: sherlock47 on Thu 12 Sep 19 at 10:41
 Hot water cylinder stat setting - smokie
I've seen conflicting reports on tank temp. Could be as low as 49.

I am going to drop it to 55 also find something as suggested above to insulate it a bit more. It's not worth spending real money on!!
 Hot water cylinder stat setting - Bromptonaut
>> I've seen conflicting reports on tank temp. Could be as low as 49.

I think the reports differ is because there are conflicting reasons for selecting a temperature.

Pretty much everything I've read suggests 60 as best for killing bugs.

Those advocating a lower temperature, and this is where 49 comes in, are worried about scalds. Debate in this paper:

Another issue with lower temperatures is that more hot water is likely to be drawn as users add less/no cold at mixer to attain same temperature at shower head or in washing up bowl. Cylinder empties sooner and/or drops to tepid unless boiler is fired.

One place we lived with a small tank and E7 electric heating we kept the water at 75 to minimise draw when washing up etc. OTOH with gas, since we both gave up full time 9-5 work, we've left boiler on at timer all day. We were regularly having to 'knock it on' during day, partly because we were showering later, after clock went off, and also because we run hot water during day for domestic stuff; hand washing cups/plates, mopping floors etc.
 Hot water cylinder stat setting - Manatee
Just checked the stat and it is actually set at 60 - a chap came a few weeks ago to do a certificate and I think he must have changed it without telling me.

TBH the water doesn't feel that hot.
 Hot water cylinder stat setting - Crankcase
Out of interest, I took this one the other way, and looked to see what I could find about legionella, the effects it might have, and the chances of getting it.

Executive summary at first pass:

Effects seem to range from "not much actually" in 70% of those that get it, to something called "death", which is a blow for the other 30%. Our resident GP might say something else?

Tiny chance of getting it in the UK (but that might be because everyone has their water temperature at 60 of course). Couple of hundred-ish cases in total 2016. So about 65 deaths that year, to compare with other causes of death if you fancy.

Further, if you're going to get it at all, looks like you're probably going to get it in a non-domestic environment. Words like "most infections" and "cruise ships" bandied about.

I couldn't find any data relating the couple of hundred a year that die of it each year with their domestic tank temperatures. I bet it's not recorded. Or someone else might do better.

I have to say we run our tank at well less than 60, because we just don't like the water being that hot from the taps. As above, I'm being complacent, possibly wrongly, and thinking it's such a tiny risk I'd rather save the cash/energy/world's resources/cute lickle puppy dogs, thanks.

My next post will be from the hospital, where they have already reserved a bed for me in the Hubris Ward.

 Hot water cylinder stat setting - Bromptonaut
In the fit and young legionella is a bit like flu; a nasty fever etc but the immune system does it's job and you get better.

Those who succumb tend to be older, less fit and possibly immunocompromised. It's called Legionnaires for a reason......
 Hot water cylinder stat setting - Fursty Ferret
I used to keep mine set at 55 and cranked it up to 65 once a month to kill anything in the tank. Combo boiler in new place so no issues.

Not convinced about legionaries in domestic water supply, believe the most common source is actually screen wash (big tank of water kept at the perfect temperature and then misted over the windscreen).
 Hot water cylinder stat setting - Kevin
The legionella in my screenwash are too high on ethanol and apple scent to cause any trouble.
 Hot water cylinder stat setting - CGNorwich

>> Not convinced about legionaries in domestic water supply,

Nor am I . I think they all went back in 410AD :-)
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