Hot water heating - oil or off-peak electricity?

KGR54

I use my oil fired boiler to heat my hot water cylinder but I have just looked into getting an EV electricity tariff that gives me an off-peak rate of £0.09/kWh. Oil is now at £1.15/litre.

Has anyone a method of calculating which is cheaper, oil or electricity?

Rodders53

1 litre of Kerosene is roughly 10kWh. So 11.5p/kWh or nearer 14p when including the inefficiency of burning it.

Wear and tear on the emergency backup immersion heater may make you regret using it long term.

Also check how much extra the day rate is cf a single rate for the rest of the house use.

EDIT Do ensure that any timer you use is suitably rated and ideally no 13A fuses anywhere —- like granny chargers long term immersion heaters will heat up those connections!!!

QrizB

A litre of oil is ~10kWh, which at £1.15/litre would be 11.5p/kWh.

Also your boiler isn't 100% efficient so it's probably closer to 13p/kWh of useful heat delivered to your HW tank.

Newbie_John

You will also need to consider that having EV tarrif increases your day rate by about 20% (Octopus same rate all day 27p/kWh vs all EV tarrifs around 33p/kWh from 5:30-23:30) so lets say if you mostly used electricity during the day and paid £500 now ot may cost you £600..

But if you already have kWh hungry EV and/or happy to shift some usage (dishwasher/washing machine) over night then it can be ignored really.

sheenas

Maybe consider an ev tariff with a battery. While electric heat is going to be a too big load for the batteries, other loads while be fine. The question then remains how to keep in the evenings.

KGR54

Thanks everyone for your very helpful advice.

The washing machine and dishwasher are easy to set a delay to an off-peak period. The car has a delayed charging start function. So, all good for overnight electricity but the remaining concern is wear and tear on the immersion heater and whether the existing one is long enough to heat the whole cylinder. Something for me to look into!

lohr500

https://forums.moneysavingexpert.com/discussion/comment/82138327#Comment_82138327

Does your immersion tank have a single element, or two?
If two, then usually the lower one is mounted near the bottom of the tank and is designed to heat a full tank of water during off-peak rates, with the upper one providing a controlled boost facility when needed.

If it is a traditional tank, with one immersion heater mounted on the top, you may be able to get the model details off any identification plate attached to it.From this you can determine the length.

We run our 3 ft long immersion heater daily during off-peak and are on the same element after 6 years.
But we have very soft water so no limescale build up.

The immersion heater elements are cheap enough to buy at around £40 and easy enough to replace so long as the failed one hasn't seized solid into the threaded part of the tank. Some fitters apply threaded joint sealing paste to them which makes removal difficult. I ended up having to carefully drill through the old element without damaging the threads on our tank to replace it.

Ectophile

EDIT Do ensure that any timer you use is suitably rated and ideally no 13A fuses anywhere —- like granny chargers long term immersion heaters will heat up those connections!!!

When my boiler went wrong over Christmas, I had to use the immersion heater instead. The airing cupboard started smelling of old fish. It was the old switch and 13A fuse getting excessively hot.

So I went out to a DIY shed and bought a 20A switch with no fuse. No more smells.

That fuse was never necessary. There's a perfectly good 16A breaker in the consumer unit to protect the immersion heater circuit.

sheenas

indeed 13a fuse spire are not recommended and a 20a double poll switch will be far more durable.

QrizB

I can only speak from my own experience but I've had immersion heaters connected via 13A fused connection units for 30 years (including 9 years of E7 where they were used daily) and haven't had any problems.