# Should an immersion be left on all the time



## HouseHunter (30 Jan 2007)

I've had some conflicting advice about this issue lately. The only way we can heat our water is the immersion. I was recently told that if you leave it on it will virtually regulate itself, and that it costs more to switch it on and off all the time. However, I have also been led to believe that using the immersion uses a lot of electricity and therefore costs a pack. 

Can anyone put this issue to bed?


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## pinkyBear (30 Jan 2007)

Hi there, we used to only be able to heat the water by emersion, very expensive.


> and that it costs more to switch it on and off all the time


 
I dont understand how it can cost you more to have it turned off.

However I do think there are timers out there that will turn on and off the water during the day, to save you having to get up in the am...


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## MsGinger (30 Jan 2007)

Yeah, I'm not sure about this one either my OH reckons a plumber told him that the most leccy is used from the initial heating up of the water and once the water is hot it's more efficient to leave it on.

However when we did this, our leccy bills did go right up!


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## hotlips (30 Jan 2007)

You could get yourself one of these gadgets:
[broken link removed]
and find out how much you're electricity using.
It only shows current usage though. It doesn't store data.

(I have no connection with Electrisave or the guy selling them in Ireland. I just got one last year and find it great.)

I don't use the immersion at all so have idea how much electricity it uses.


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## ClubMan (30 Jan 2007)

Definitely *do not *leave the immersion on all the time unless it's on a timer (e.g. a night rate timer whereby it will heat for a few hours on the night rate giving you a full tank for the next day)!


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## Satanta (30 Jan 2007)

It's similiar to people saying you should leave lights on as the (re)turning them on uses more electricity and don't turn your car off if only stopping for a short time as the ignition will use up more fuel (an interesting thread on this on boards.ie or octane.ie a short time back. I think they got a figure from somewhere giving 3 1/2 minutes for an average family car to be stopped before it should be [from a fuel economy point of view] turned off - but I am a little hazy on the details).

An emersion is very expensive. Obviously each home is different, but I'd imagine for leaving it on all the time to be more efficient you'd need to be turning it on numerous seperate times (morning, mid-day, evening and night). The best way to save with the emersion bill would be to organise things so it only needs to go on once a day, reduce the amount of water used where possible (good for the environment too) and don't forget to turn it off.

I've never seen any stats to back up leaving it off, but I've never seen any to contradict it either!


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## gd2000 (30 Jan 2007)

There's absolutely no right answer to a question like this.  It really depends on when you use the water and how much you use.  For the majority of people though, it's unlikely to save money by keeping it on all the time.  Good insultation is extremely important.

As MsGinger says - anecdotal experience works best.  Try it for a week and see how your meter reading changes...


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## ClubMan (30 Jan 2007)

Say an immersion has a 3kW element. If you leave it on 24 hours a day then that will cost c. 3 x 24 x €0.16 on the urban domestic (day rate) tariff or €11 a day. In practice the element will probably not be running at full pelt all of the time and there will most likely be a thermostat switching it off and back on when the temperature of the water falls but this illustrates how costly leaving it on all the time could be. You should really only heat water as you need it. If you have a night rate meter then it might make sense to have the water heat for a few hours overnight leaving (with a well insulated tank - ideally an integrated/sprayed on lagging jacket) enough water for during the day. That's the way most night rate systems are set up to work anyway.


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## davidoco (30 Jan 2007)

You should look at adding a simple time clock beside your immersion switch which will heat the water only when you want it.  

Leaving it on all the time is like having the kettle constantly on the boil 24 hours but you only use it 4 times a day.


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## davidoco (30 Jan 2007)

hotlips said:


> You could get yourself one of these gadgets:
> [broken link removed]
> 
> It only shows current usage though. It doesn't store data.




Maybe something on this website will help if your interested in monitoring your ESB usage.

http://www.rfxcom.com/sensors.htm


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## z107 (30 Jan 2007)

> It's similiar to people saying you should leave lights on as the (re)turning them on uses more electricity



Not quite similar for certain florescent lights. Some lights require a capicitor to be charged to start the light. This can use more electricity than leaving the light on (depending on how many times you switch it off an on)


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## Satanta (30 Jan 2007)

umop3p!sdn said:


> Not quite similar for certain florescent lights.


I'd still suggest it's very similiar. The theory is exactly the same.

If I were to leave a room with the said florescent light, there would come a time when it would have been cheaper/more economical to have turned it off. It just depends on the light, the time I'll be gone etc to decide if I should or not. The time for a given light could possibly be 2 days, but it's still the same theory. The fact that the answer is one that makes turning it off improbable, doesn't change the theory that underpins it. 

I didn't list those examples as urban legends which are wrong. The petrol one was quite scientifically backed, I just wish I remembered the exact times it gave, 3.5 mins is definatly bouncing around my head (although it would have to be altered slightly to myown car even if I were to follow it).

For an emersion, I'd probably guess you'd need to be using it anything from 3 to 30 times a day before it would be worth leaving on (absolute random guess, I have no idea what it might be, I'd just assume it would be high). It's still the exact same theory behind it.


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## wolfspeed (30 Jan 2007)

The other thing to think about, is getting a fully insulated boiler. There are a couple on the market, the one I got (cost around €800) looses one degree of heat a day. So when you stick it on for a couple of hours, you can have hot water for a couple of days. Obviously this will depend on how many people are using the water.


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## ClubMan (30 Jan 2007)

wolfspeed said:


> The other thing to think about, is getting a fully insulated boiler.


You mean fully insulated immersion tank I presume? Unless you plan to generate your own electricity or something?


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## Purple (30 Jan 2007)

ClubMan said:


> You mean fully insulated immersion tank I presume? Unless you plan to generate your own electricity or something?


Pedantic?


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## ClubMan (30 Jan 2007)

I never heard the immersion tank referred to as a boiler.


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## Hoagy (30 Jan 2007)

Doesn't the rate of heat loss depend on the temperature difference between the hot water and the surrounding air?
So the longer your hot water cylinder remains at it's highest temperature, the more heat it will lose.


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## z107 (30 Jan 2007)

It can be easily calculated if you know the size of your immersion, the initial water temperature and the final temperature.

It takes 4.184 Joules to raise 1 gram of water by 1C
Start temperature of water is about 10C
End temperature is about 70c
1 Litre of pure water is 1kg = 1000grams
Size of tank = 100 litres?

We want to raise 100000 grams of water by 60C
This will take 418400 x 60 = 25104000 Joules

A Joule is the work done to produce power of one watt continuously for one second, or 2.7778 ×10−7 Kilowatt-hours.

So to heat your tank from cold, it will take about 6.97kWh

Compare this to how much heat we lose with an immersion left on.


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## ClubMan (30 Jan 2007)

And I thought that I was bad! 

Anybody ever monitored their fridge temperature?


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## usrbin (31 Jan 2007)

No expert in this area, but is it possible some of the conflicting advice given to the OP arises from confusion over having the immersion ON (i.e. actually heating) and having it OPEN?

E.g. on our setup there's a featureless switch built into the system, beside the tank, which - if I understand correctly - just controls whether a valve is open or closed.  TBH I'm not sure why it's needed so prominently - perhaps someone can clarify - but our impression is that (a) it should be left in the one position (OPEN) all the time and (b) it's common enough to have this setup in modern installations.

Just a thought.


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## ClubMan (31 Jan 2007)

Or alternatively having a _Nightsaver _timer switch which is left on all the time but which only actually kicks in for a few hours at night on the discounted rate to heat water for the next day? There is also a manual boost switch for heating water on demand if the water heated overnight runs out.


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## Hoagy (31 Jan 2007)

ClubMan said:


> Or alternatively having a _Nightsaver _timer switch which is left on all the time but which only actually kicks in for a few hours at night on the discounted rate to heat water for the next day? There is also a manual boost switch for heating water on demand if the water heated overnight runs out.


 

Nightsaver is not such an attactive option since 1st January, now that the ESB charge you €244.03 to fit the dual tariff meter.
According to the ESB website, you need to transfer 5 units from day to night every day for three years to recoup the cost.
Sort of penalising you for thinking about energy saving?


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## ClubMan (31 Jan 2007)

I'm not saying that _Nightsaver _or electricity generally is necessarily the best option but some of us (in _Goldshield _homes) are stuck with it short of doing a big conversion to some other alternative.


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## gd2000 (31 Jan 2007)

Inspite of all the theories the *only* way to know for certain is to test it.

Try it for a period of time (a day, a week?) and see how it affects your meter...


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