Oil versus Electricity For Heating Water

kah22

Given the price of oil, a condenser boiler running at 94 % peak performance, a new fully covered hot water cylinder. Would it be more economical to heat a full tank of water, once or twice a week using oil or electricity? Is there a way of working this out?

This question applies to Northern Ireland where the cost of electricity/oil is among the highest in the UK. Gas is not currently an option. I use Power NI and pay by DD

While this is a particular question it might well open up a discussion as to the pros and cons of electricity versus oil.

As always many thanks for your answers

HouseACA

I've wondered the same myself. Whilst I don't know the figures, it appears to me that if I run the oil heating (with radiators off) the water seems to heat up quicker and stay hot longer than using the immersion.

It's really only a problem for us in summer when you don't need heating on, but then have no hot water. Not so bad coming in to winter, as we will need to start heating house anyway.

malc_b

Depends on whether you mean full price electric or E7 night rate. E7 night rate would be cheaper but in order to break even on E7, where daytime electric is more than single rate, you'd need to move washer machine, tumbler dryer, dishwasher to night time.

Next point is that you won't get 94% efficiency from you oil boiler as that depends on a low return temperature and when heating a tank it will be a hot return.

You're also likely to have the boiler short cycle. I know mine does. Basically the boiler puts out 15kW but the hot water tank can't absorb that rate of heat. Hence the you get short cycling where the boiler thermostat is cutting in and out. I set my time clock up to give 10 minute run with 10 minute rest, repeat 3 times. I found that 10 minutes was how long it took before the boiler started short cycling which was a 2 minute cycle so this improved the efficiency.

warmhands.coldheart

HouseACA wrote: »

I've wondered the same myself. Whilst I don't know the figures, it appears to me that if I run the oil heating (with radiators off) the water seems to heat up quicker and stay hot longer than using the immersion.

It's really only a problem for us in summer when you don't need heating on, but then have no hot water. Not so bad coming in to winter, as we will need to start heating house anyway.

Does your system not let you select between Hot Water, Heating or Heating & Hot water. I don't know why some houses are built like this? Possibly worth adding thermostatic valves to your Rads so the water heats up without heating the Rads or having he system modified to allow for the above. Could simple be a case of adding a 3 Port and new timer and a bit of extra wiring depending on where your boiler is.

gibbyni

I had been wondering the same thing so did a few calculations. last summer I had been using the boiler to heat water over the summer and was costing ~ £1.00 a day but would give me a full tank of hot water for the day.

This summer I have been using the electric heater, this works out at abour 40p per hour and would take about 2 hours to fill the tank.

So for me the electric has been better but that will change next month when the heating goes back on.

Just to note im in a large house with a rubish boiler, so im probably paying over the odds anyway for heating.

Also I prepaid for my electric at the start of the summer. before Budget did their price increase

kah22

malc_b wrote: »

Depends on whether you mean full price electric or E7 night rate. E7 night rate would be cheaper but in order to break even on E7, where daytime electric is more than single rate, you'd need to move washer machine, tumbler dryer, dishwasher to night time.

Next point is that you won't get 94% efficiency from you oil boiler as that depends on a low return temperature and when heating a tank it will be a hot return.

You're also likely to have the boiler short cycle. I know mine does. Basically the boiler puts out 15kW but the hot water tank can't absorb that rate of heat. Hence the you get short cycling where the boiler thermostat is cutting in and out. I set my time clock up to give 10 minute run with 10 minute rest, repeat 3 times. I found that 10 minutes was how long it took before the boiler started short cycling which was a 2 minute cycle so this improved the efficiency.

Great answer.

Thought 94% was what my boiler man told me last time round. I'll check that at next service.

I'm on the normal Power NI tarriff..

My oil system is split so that I can have heat OR hot water independantly of each other

To be honest I don't really understand my indoor timer. I know basically two options. Turn it on let it run for an hour and it turns off automatically after the hour, or when I turn it off. Or let it run indefinately until I turn it off. Again I can turn off at any time. There are other automatic settings but I've never really understood them. Not good that

My guage is set to 18. I take it that is 18 celsius

kah22

I've heard it said that if you are not using that much water that it is just as cheap to leave the hot water heater on all the time rather than always warming the tank from cold. What do you think?

ballyblack

myth busting


http://www.moneysavingexpert.com/utilities/energy-saving-myths#heatingon

HappyMJ

kah22 wrote: »

I've heard it said that if you are not using that much water that it is just as cheap to leave the hot water heater on all the time rather than always warming the tank from cold. What do you think?

Sounds fine...I do that and I've turned the temperature of the water right down so it's not so hot. The immersion heater only comes for a few minutes every few hours if no water is used to bring the temperature back up.

GlynD

My opinion would be that burning oil for a few minutes would give you what you want and be cheaper than using your immersion heater. In saying that I know that I can get extremely;y hot water within five minutes with the immersion heater installed in this house so I tend to use it when I need some hot water quickly.

I don't know why this should be and what the money saving qualities are as I'm no specialist. Perhaps it's because the immersion heater we have is a higher wattage than others we've had in the past. (Passing electricians could maybe comment).

sheerdelight

Glynd
The reason you get hot water in a few minutes is that you have an external Willis type immersion heater. It heats a small amount of water in a heater at the side of the main cylinder and feeds it in to the top of the tank. Hot water becomes available within a few minutes of switching it on. This type of heater is popular in Northern Ireland where it was originally designed and (is still?) manufactured.

Compare this to the immersion heater that goes inside a hot water cylinder. Often featuring two elements this has to heat the whole tank. You wait ages to heat water as you are heating the whole tank of water and the temperature rises slowly. These are commom in GB and also present here unfortunately. Maybe OK if you have Economy 7 off peak heating, but at any time of the day or night, very slow.

Even if my oil burner could heat water only I would still prefer to use a Willis type to heat water as you can switch it on to heat for a few minutes for a few litres of hot water or leave it on for as long as necessary to heat the whole tank. Depends what your requirements are.

Washing machines these days only have a cold feed as do dishwashers. Some people may have showers or baths that do require cylinder stored hot water. If you have electric showers too there will be even less need for large tanks of hot water.