# Which is cheaper to heat water, an immersion heater or oil?



## GingerCat (17 Sep 2011)

Our central heating boiler currently heats our hot water, but we're thinking of installing an immersion heater instead. Which is cheaper to run?


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## RMCF (17 Sep 2011)

I'd guess oil.


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## Guest105 (17 Sep 2011)

Oil


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## GingerCat (17 Sep 2011)

Ta, just spoke to a plumber and he agreed!


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## hastalavista (17 Sep 2011)

without knowing the efficiency of the boiler and the plumbing layout, including the length of the pipe run from the boiler to the cylinder, its not possible to answer this question


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## RMCF (17 Sep 2011)

hastalavista said:


> without knowing the efficiency of the boiler and the plumbing layout, including the length of the pipe run from the boiler to the cylinder, its not possible to answer this question



so oil then!


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## quentingargan (18 Sep 2011)

In winter, it is oil. Most of the inefficiencies of the system, pipework etc., are taken up by the home heating, so your boilder is heating the cylinder on its way to the radiators. That is why solar works well

In summer, that is often not the case. Heating a boiler, flue, and 20M of pipework just to bring 120L in the hotpress from 30 to 60 may be more expensive than using the immersion - particularly if you have a dual immersion, and you are only heating the "sink" part. 

However, cheapest of all if off-peak electricity at night. If you have a very well insulated cylinder so that heat loss in the daytime isn't too severe, and/or you shower and use hot water in the early part of the day, that might be best of all. 

It is cheaper to boil a kettle to wash the dishes than it is to use either oil or the immersion...


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## onq (18 Sep 2011)

quentingargan said:


> In winter, it is oil. Most of the inefficiencies of the system, pipework etc., are taken up by the home heating, so your boilder is heating the cylinder on its way to the radiators. That is why solar works well
> (snip).



Just to clarify, are you saying that this is why solar works to well in the winter, or do you mean separately, or what?


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## hastalavista (18 Sep 2011)

quentingargan said:


> In winter, it is oil. Most of the inefficiencies of the system, pipework etc., are taken up by the home heating, so your boilder is heating the cylinder on its way to the radiators. That is why solar works well
> 
> In summer, that is often not the case. Heating a boiler, flue, and 20M of pipework just to bring 120L in the hotpress from 30 to 60 may be more expensive than using the immersion - particularly if you have a dual immersion, and you are only heating the "sink" part.
> 
> ...



Does the off peak power not have an addition standing/meter charge that has to be factored into the price per watt?


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## quentingargan (18 Sep 2011)

ONQ - My point is that there is a good synergy between solar and normaly central heating systems, because in winter, when the solar isn't working, the heating is providing hot water at a lower cost. 

Agree with hastalavista that you have to factor in the standing charge, but we will all be stuck with smart meters down the line. The introduction of wind and other renewables on the grid will bring about the need for "demand side management" moving consumption to off-peak time. So we will find ourselves incentivised to use more off-peak power. 

The difference in the standing charge is, in most cases, easily recovered anyhow with just moderate behaviour change. Remember that freezers, fridges etc., all run through the night, and in the summer, night rate extends to 9.00am.


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## SparkRite (18 Sep 2011)

hastalavista said:


> Does the off peak power not have an addition standing/meter charge that has to be factored into the price per watt?



Indeed it does, that is why its make commercial sense to use more electricity at night (off peak) than during the day to offset the additional standing charge.


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## DavyJones (22 Sep 2011)

There is a really interesting thread here somewhere on this very subject. It had some fine mathematicians working out the cost per unit of electricity, gas and oil. It then worked out how much of each it took to heat a stated amount of water from 10C to 60C. 

I'll have a search for it.


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## quentingargan (22 Sep 2011)

DavyJones said:


> There is a really interesting thread here somewhere on this very subject. It had some fine mathamatiinscs working out the cost per unit of electricity, gas and oil. It then worked out how much of each it took to heat a stated amount of water from 10C to 60C.
> 
> I'll have a search for it.


There is also this [broken link removed]from SEAI...


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## DavyJones (22 Sep 2011)

quentingargan said:


> There is also this [broken link removed]from SEAI...




I suppose, but it isn't half as much fun as that thread


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## Leo (23 Sep 2011)

DavyJones said:


> There is a really interesting thread here somewhere on this very subject.


 
This the one?


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## DavyJones (23 Sep 2011)

Leo said:


> This the one?




Sadly no. The thread is a few years old now and went on for a bit with lively debate.


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## onq (23 Sep 2011)

quentingargan said:


> ONQ - My point is that there is a good synergy between solar and normaly central heating systems, because in winter, when the solar isn't working, the heating is providing hot water at a lower cost.



I'm not sure how any lower cost arises when the solar isn't working, but perhaps I'm just not picking up on a simple point you're trying to make to me.


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