Immersion heater time taken to heat a tank of water

[JohnD]

it will raise the temperature by 180000/4.19/1000=43°

Which, amazingly, is about the rise needed from incoming cold supply to hot tapwater.

 

[stillp]

it will raise the temperature by 180000/4.19/1000=43°

Not allowing for loss of heat to ambient.

 

[JohnW2]

deleted

 

[JohnW2]

it will raise the temperature by 180000/4.19/1000=43°

Which, amazingly, is about the rise needed from incoming cold supply to hot tapwater.

It is ... but hot water cylinders usually contain a lot more than 1 litre of water!! If the immersion is heating N litres, you have to divide that 43° (per minute) by N.

Kind Regards, John

 

[JohnD]

But that's why I said "an immersion heater warms the water at a rate of about one litre per minute"

So a 10-litre washing up bowl might take about ten minutes, and a 50-litre shower might take about 50 minutes, and a hundred-litre bath about 100 minutes

(very rough approximations especially for small numbers as you need to build up a layer of hot water at the top)

The stratification prevents it warming 100 litres by 4degrees.

 

[JohnW2]

But that's why I said "an immersion heater warms the water at a rate of about one litre per minute" So a 10-litre washing up bowl might take about ten minutes, and a 50-litre shower might take about 50 minutes, and a hundred-litre bath about 100 minutes.

That is, indeed, all true - but I thought that people just reading your most recent comment may well not have realised that's what you meant!

As I said earlier, "1 litre per minute' for a 3kW immersion to heat water through the typically-required temperature rise is a very good rule of thumb.

Kind Regards, John

 

[JohnD]

 

[john4703]

Is it possible that the immersion heater you fitted was a dual type? There used to be some with two elements, one only heats the top section of the immersion heater and thus only the top part of the water, the other heats the whole length. I think the logic was that you had two switches, one for small amounts of water, the other for the whole lot. It was supposed to save money by not heating excessive amounts of water. I fitted one like that about 4 years ago in Southern Ireland but have not seen one in the UK for a long time.

 

[JohnD]

I tried to get one a few years back, but the makers (might have been Sadia?) said they have been discontinued.

 

[JohnW2]

Is it possible that the immersion heater you fitted was a dual type? There used to be some with two elements, one only heats the top section of the immersion heater and thus only the top part of the water, the other heats the whole length. I think the logic was that you had two switches, one for small amounts of water, the other for the whole lot. It was supposed to save money by not heating excessive amounts of water. I fitted one like that about 4 years ago in Southern Ireland but have not seen one in the UK for a long time.

They still exist (in UK), but are not widely socked (e.g. click here ). As you say, it's just possible that the OP has one of those, but has the 'short' element connected. Alternatively, as has been suggested, he might possibly have a short thermostat in a long element.

Like many, I have the equivalent, using two 11" (or are they 14"?) ones. The one at the bottom heats nearly the whole tank (on E7 electricity at night) whilst the one at the top is used for small-volume daytime 'topups' if required.

Kind Regards, John

 

[PBC_1966]

Is it possible that the immersion heater you fitted was a dual type? There used to be some with two elements, one only heats the top section of the immersion heater and thus only the top part of the water, the other heats the whole length. I think the logic was that you had two switches, one for small amounts of water, the other for the whole lot. .

Or the old "Sink / Bath" changeover switch.

 

[Horatio1960]

Sorry got waylaid into other duties

Thank you all again for your input

Just to clarify, the immersion is the *only* form of heating water we have, no other heating of any sort, so am reliant on the immersion creating enough hot water
(thank goodness my three daughters are not still at home as there would be riots
To ericmark no never heard of the Willis system although interesting I am not in a position to be able to fit one, so am stuck with the system I have unfortunately

Length of immersion is 27" , I have measured the approx position of the top mounted immersion element and at its lowest point is at virtually the same level in the tank as the original low mounted 14" element

So as far as I am concerned should do at least a comparable job as the low mounted 14" element but is significantly worse

As to temperature, our old one which ran for some 17 years at 55 degrees, provided suffient hot water for the majority of occasions with four women in the house
It is now set at 60 degrees, and will scald the hand if you are not careful at first (but not for long) so am loath to turn it up even higher and why did the old one heat well enough at 55 degrees

I may try running it for 24 hours as a test, but all advice I have read states running 24/7 is not economical, for the first ten years or so we ran it permanently on, I fitted a timer and set it to run three hours a day and cut power usage considerably

The element I fitted was a standard 27" element with resettable thermostat which conforms to the standards effective Apr 2004, they don't even list a dual element in their catalogue

I haven't had a chance to check the length of the thermostat as it involves partially dismantling the airing cupboard but aim to do that in the next day or so

Whilst the old lower mounted immersion was I think more efficient as the element was wholly low down horizontal across the tank, I cannot believe that a longer element although mounted diagonally top to bottom would be so drastically different as to make it necessary to run it for over double the length of time to produce a third of the hot water and with a modern thicker lagging

Thank you again for all the feedback, much appreciated

 

[kai]

I always believed that a side entry element at the bottom was more efficient at heating the water, as there were fewer losses, as the rising heat from the element was almost all used in heating the water, and not the ceiling instead.

 

[JohnW2]

I always believed that a side entry element at the bottom was more efficient at heating the water, as there were fewer losses, as the rising heat from the element was almost all used in heating the water, and not the ceiling instead.

Indeed. As I said, that's what I've used as my primary means of water heating for the last few decades. However, I think that virtually all of the heat will go into the water (rather than 'the ceiling'), at least initially, even for a top-entry one!

One significant (albeit only occasional) advantage of top-entry ones is that one has to do minimal draining of the system in order to replace them

Kind Regards, John

 

[333rocky333]

Is it not just a case that the stat is turning off the element, due to the 55deg temp at the top of the tank, before heating the bottom section fully.
whereas the old bottom element may have run longer as the bottom never really got to 55 deg much but the majority of the top part of the tank also got heated, hence more hot water.
Although on for 4 hours the stat wont usually let it run for the whole 4 hours, yet a longer time gap between use would allow the heat to radiate around the tank water more, even with the element off, wouldnt it