Cheaper water heating: oil or elec?

RebTech

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I recently got oil-fired central heating with a condensing but not combi boiler (low pressure water supply). The HW cylinder has both a top-mounted immersion heater and a coil for the boiler. So my question is: when the central heating is OFF, will it be cheaper to heat water using oil or electricity, or won't it make much difference? I'm assuming that when the CH is on it will be more efficient to have the boiler heat the water as well. I have just a standard electricity meter.

jepsonclough

I was going to post a very similar question. However, there is one key factor to take into consideration that was omitted from the original question: the relative prices of the two sorts of energy.

When I first moved in here, ten years ago, oil cost about 16p a litre but now it is more typically 60p and can be over 70p. In comparison, I am paying about 12p a unit for electricity. Ten years ago, the use of oil seemed a no-brainer but now I'm not so sure This is regardless of whether or not the oil is being used for heating at any given time and, paradoxically, it may be better to use oil for hot water when it is not being used for central heating because the purchase price depends on supply and demand and so is much higher in the winter.

Clearly there must be an issue of efficiency but I would think it is very difficult to assess that without knowing the detailed performance of the individual boiler. So the question I would ask would be how the energy you can get out of 1 litre of heating oil (in a modern, efficient boiler) compares to the energy from spending the same amount on electricity. In my case, this boils down to:

does 1 litre of oil give you more heat energy than 5 units of electricity?

macman

Oil about 6p per kWh, electricity about 12p per kWh (on Standard tariff). Even allowing for the lower efficiency of an oil-fired boiler, it's still cheaper.

RebTech

After posting the question I did some digging and found similar figures to what macman quotes. But also, I discovered that a typical modern condensing boiler is >90% efficient. So oil comes out quite a bit cheaper overall.

jepsonclough

Thanks macman - I'll turn the immersion off at once!:j

nande2000

I would figure in 20% loss of efficiency for oil due to heat loss with the pipes, you dont get that with an immersion as it goes straight to the cylinder. So a >90% efficient oil boiler is more like 75% efficient.
Then figure in the servicing costs for an oil boiler (no servicing required for an immersion).

Oil is still cheaper, but for how much longer ?

macman

I think you'll find that rising oil and other fossil fuel prices lead to rising electricity prices...