Cheaper to use electric immersion heater ?

ICV

With the current high price of heating oil I'm wondering if it would now be cheaper to use electricity to heat water using the immersion heater ?
Wouldn't know where to start to get the numbers required to work it out though

HappyMJ

It's cheaper if you have an E7 tariff and a timer to only use the immersion at night rates. Otherwise it's a close call. What's the unit charge on your electric bill and what's the per litre price of the oil? There is about 10kwh in a litre of oil so divide it by 10. If higher than electric then use electric. To be really accurate you also need to know the effiency of the boiler.

ICV

Well, my average electricity unit cost is ~11.63p and I've been quoted 64.04p/litre inc VAT today for oil so my (10 years old) boiler would need to be less than 60% efficient to make it cheaper to use the immersion heater - I think.

bobmedley

A 10 year old boiler would be somewhere between 83% - 94% efficient (check your model on the SEDBUK site).

That means at 64.04p per litre and taking the worst case efficiency of c83% then the oil cost per kw would be c7.5p, so it's over 50% more expensive to use the immersion heater at non-E7 rates.

Cardew

bobmedley wrote: »

A 10 year old boiler would be somewhere between 83% - 94% efficient (check your model on the SEDBUK site).

Plenty of heating engineers would argue that no boiler, not even a new one, will ever achieve 94% efficiency outside of a laboratory!

The SEDBUK figures are much like showroom MPG figures for cars - rarely achievable. I think the EST talk about an average 75% reliability.

bobmedley

I appreciate that, although it's the only constant you can use to try to make any kind of comparison.

My oil boiler is 84% efficient according to SEDBUK (it's non-condensing by the way) and when I have a service the test results are very thorough and the last datasheet stated that Nett Efficiency was 80% - a 4% drop for a 12 year old boiler then? That sounds feasible.

Any heating engineers care to comment?

Cardew

bobmedley wrote: »

I appreciate that, although it's the only constant you can use to try to make any kind of comparison.

My oil boiler is 84% efficient according to SEDBUK (it's non-condensing by the way) and when I have a service the test results are very thorough and the last datasheet stated that Nett Efficiency was 80% - a 4% drop for a 12 year old boiler then? That sounds feasible.

Any heating engineers care to comment?

How on earth would they check the efficiency in situ?

They would need a hugely complicated test rig to measure the calorific output of the boiler - bearing in mind the hot water goes to radiators and hot water tank.

Also a very accurate flow meter for the oil(or gas).

I can't believe they are measuring anything; sounds like guesswork at best.

meatsweats

I have been testing this out for the last week, having switched off my heating. I currently use about £20 worth of electricity a month and based on meter readings from the last weeks estimate this will go up to £30 for using my immersion heater, rather than oil heating. I've just filled my oil tank and think that based on £10 a month addition to my electricity this will far outweigh the instability of using oil. Pacing your oil consumption (by using immersion heater, switching off economy on washing machine) this should give more flexibility with buying oil, rather than using so much you have to fill up at a peak price time

meatsweats

I should add that that is based on a three bed end terrace, single occupancy and using around 800 litres a year of oil

bobmedley

Cardew wrote: »

How on earth would they check the efficiency in situ?

They would need a hugely complicated test rig to measure the calorific output of the boiler - bearing in mind the hot water goes to radiators and hot water tank.

Also a very accurate flow meter for the oil(or gas).

I can't believe they are measuring anything; sounds like guesswork at best.

???:o

They use one of these

http://www.kane.co.uk/online-catalogue/kane455kit

All the parameters to calculate efficiency are within the boiler combustion chamber - it's nothing to do with oil flow, the hot water or anything else.

Cardew

bobmedley wrote: »

???:o

They use one of these

http://www.kane.co.uk/online-catalogue/kane455kit

All the parameters to calculate efficiency are within the boiler combustion chamber - it's nothing to do with oil flow, the hot water or anything else.

Well I am no heating engineer, and haven’t experience of Oil CH for many years; but I wouldn’t have thought that measurement of combustion efficiency would give a figure for overall boiler efficiency(i.e. to compare with the SEDBUK figure). There are other factors to be considered, pilot light, heat exchanger etc. Indeed the water temperature is a factor.

I have also never been given an efficiency figure for Gas – which the apparatus you show also tests.

This is how WHICH tests boiler efficiency:

How Which? tests boiler efficiency
Boiler efficiency is a key part of our independent boiler tests, which meet European standards. We check each boiler to see how much of the gas it burns is converted into heat. This measures the boiler's efficiency.

As do SEDBUK

Boiler efficiency is rated as a percentage assessing how much of the fuel that they consume is converted to heat. This rating is called SEDBUK – Seasonal Efficiency of Domestic Boilers in the UK and represents the average annual efficiency achieved in typical domestic conditions.

Also with condensing boilers(I know yours is not condensing) the efficiency is dependant on return water temperature.

Just my thoughts but freely admit I could be wrong - be interested opinions of heating engineers.