Will it be cheaper to use immersion to heat water now

RedQueenie

Hello, I'm not sure if there is a quick answer to this but I was wondering if it would be cheaper to use an immersion heater to heat the water in the tank rather than use the oil boiler? The price of heating oil has shot up in the last couple of weeks and I'm trying to save as much as I can by keeping the heating off but we do need to shower. I did manage to lock in my electricity for 2 years before the prices went daft, but not sure if that would still make it cheaper to use than oil. The boiler is about 10 years old.

QrizB

There are about 10kWh in a litre of oil, but if your boiler is only 80% efficient you'll only get 8kWh out of it. (Your boiler could be more efficient than that, but we don't know.)

What are you paying for electricity, per kWh?

Multiply the price of electricity by 8 and compare that to the price of a litre of oil.

Browntoa

Rough estimate 

3kw immersion , 2 hours a day , around £500-600 a year 

6kw boiler , 2 hours a day , around £1000- 1100 a year

RedQueenie

Thank you so much for your replies. I have a Grant Vortex Pro Utility 15/26 boiler. The website says it is around 90% efficient (not sure if that drops over time) My immersion is 3kw and I pay 22.18pWh (standing charge 15.75p/day) So 22.18 x 9 gives me 199.62 which isn't far off the price of oil at the moment.

RG2015

I was just thinking this yesterday. In summer I use about 1.5 litres per day which will just be for water heating.

My last oil fill in February, cost me £0.64 per litre and this should last me until October. Therefore water heating from May to October should cost me 1.5 x 180 x £0.64 = £173.

My immersion heater is 3kw and my electricity is fixed at 16.73p until March 2023. Therefore 1 hour a day would cost £90 over the same 6 month period.

I am guessing that 1 hour a day would suffice, but it still leaves a breakeven point at about 1.9 hours per day.

And of course oil now is 2 or 3 times the price I paid in February. 



 

QrizB

RG2015 said:

I am guessing that 1 hour a day would suffice, but it still leaves a breakeven point at about 1.9 hours per day.

It will depend on how much hot water you use as a household.

My immersion only heats the top 60% of my tank (27" of my 42"-tall tank) and takes about 6kWh to do so.

RG2015

QrizB said:

RG2015 said:

I am guessing that 1 hour a day would suffice, but it still leaves a breakeven point at about 1.9 hours per day.

It will depend on how much hot water you use as a household.

My immersion only heats the top 60% of my tank (27" of my 42"-tall tank) and takes about 6kWh to do so.

We used the immersion when the boiler wasn't working (simple problem now fixed) and I seem to recall 1 hour was enough.

However, many years of indoctrination still leaves me regarding immersion heaters as the spawn of Satan!

coffeehound

QrizB said:

RG2015 said:

I am guessing that 1 hour a day would suffice, but it still leaves a breakeven point at about 1.9 hours per day.

It will depend on how much hot water you use as a household.

My immersion only heats the top 60% of my tank (27" of my 42"-tall tank) and takes about 6kWh to do so.

You would hope the designers ensured that the IH caused strong enough convection to stir the whole volume?

What capacity is your tank @RG2015 ?  There are some straightforward calcs you can do to estimate how long the IH needs to run. 

RG2015

coffeehound said:

QrizB said:

RG2015 said:

I am guessing that 1 hour a day would suffice, but it still leaves a breakeven point at about 1.9 hours per day.

It will depend on how much hot water you use as a household.

My immersion only heats the top 60% of my tank (27" of my 42"-tall tank) and takes about 6kWh to do so.

You would hope the designers ensured that the IH caused strong enough convection to stir the whole volume?

What capacity is your tank @RG2015 ?  There are some straightforward calcs you can do to estimate how long the IH needs to run. 

Thanks. As per internet (?)

210 litres, so 210 x 50 (temp rise) x 4 / 3412 = 12.3 kWh. Hence 4 hours for a 3kW IH.

Ouch!

coffeehound

One thing that's probably pessimistic about those numbers is that it assumes the tank has become as cold as the incoming mains water which is very much worst-case.  Do you find that the water is still somewhat warm even at the end of the day?  Although this is the temperature at the top of the tank, maybe the overall average temperature is say 25 C.  So the actual rise required is only 35 C.

RG2015

coffeehound said:

One thing that's probably pessimistic about those numbers is that it assumes the tank has become as cold as the incoming mains water which is very much worst-case.  Do you find that the water is still somewhat warm even at the end of the day?  Although this is the temperature at the top of the tank, maybe the overall average temperature is say 25 C.  So the actual rise required is only 35 C.

Yes, I did see this as a worst case scenario.

In practice, when we have had a boiler failure, it has taken at least two days before the water in the taps or shower became tepid.

This explains my 1 to 2 hour thoughts, and of course my morbid fear of immersion heaters!