Using Immersion heater on night rate instead of gas? 7 December 2021 at 12:13PM in Green & ethical MoneySaving 9 replies 230 views

JimLad

Hi Green Team!

My gas price just dropped on to variable rate and with no prospects of things getting cheaper any time soon i was wondering....

I am on octopus Go where electricity is 5p for a period at night...Would it be cheaper / the same price to heat my hot water during this period using the immersion heater in my hot water tank vs using my gas boiler in the day (3.9p). Ive read online that gas boilers are usually only around 80% efficient and this can drop as low as 50% if they are not doing heating at the same time (condensing mode). THis is vs an immersion heater which is in theory close to 100% efficient.

There is also the environmental argument too of using electricity which can be lower carbon (especially at night) vs gas.

Any thoughts?

QrizB

The 50% typically refers to combi boilers, but if you've got a HW tank I guess you've got a conventional boiler? If so, the price is pretty close between 5p electricity on Go and 4p gas.

I'm in a similar position and have stuck with gas but that's mostly because I don't have a timer on my immersion heater and the £20 one would cost is far more than I could possibly save!

JimLad

QrizB said:

The 50% typically refers to combi boilers, but if you've got a HW tank I guess you've got a conventional boiler? If so, the price is pretty close between 5p electricity on Go and 4p gas.

I'm in a similar position and have stuck with gas but that's mostly because I don't have a timer on my immersion heater and the £20 one would cost is far more than I could possibly save!

Right i understand! Sounds like there might not be much in it

Luckily i have an iboost which diverts excess solar in the day time. It also has a timer function

Coastalwatch

Hi JimLad and welcome to the Madhouse, as others have often mused. It's great you are considering making a change as many of us on here are already in the process of transitioning away from FF's with some even having completed the move. With a PV array and iboost already installed it would seem you're already along the road. It's great taking small steps at a time especially where the cost differences are so minor making the decision all the easier to make.

One thing often neglected with gas costs is that there is also the hidden cost of electricity in powering the circulating pump and fan in the gas flue. Maybe not massive but that 250 Watts or so when coupled to a heatpump would possibly return 1 kW of heat!

Enjoy the journey, however quickly or otherwise you take it.

arty688

I guess the situation may change at the next price rise though

JimLad

Coastalwatch said:

Hi JimLad and welcome to the Madhouse, as others have often mused. It's great you are considering making a change as many of us on here are already in the process of transitioning away from FF's with some even having completed the move. With a PV array and iboost already installed it would seem you're already along the road. It's great taking small steps at a time especially where the cost differences are so minor making the decision all the easier to make.

One thing often neglected with gas costs is that there is also the hidden cost of electricity in powering the circulating pump and fan in the gas flue. Maybe not massive but that 250 Watts or so when coupled to a heatpump would possibly return 1 kW of heat!

Enjoy the journey, however quickly or otherwise you take it.

Thanks for the welcome! I used to contribute a bit to the how much solar have you generated thread but that was years ago before i had kids and had more spare time! 

I also have an e-golf which i charge at night on GO.

I think im just going to have to switch the gas hot water off and turn on the immersion and see how it performs. I can keep an eye on costs on my online dashboard as i have a smart meter. As you say it would be really nice to burn less FF.

arty688 said:

I guess the situation may change at the next price rise though

Agreed! Gas is going to get more expensive and whilst the GO night rate might not last forever, its locked in until august next year for me.

EricMears

Coastalwatch said:

One thing often neglected with gas costs is that there is also the hidden cost of electricity in powering the circulating pump and fan in the gas flue. Maybe not massive but that 250 Watts or so when coupled to a heatpump would possibly return 1 kW of heat!

Another point worth considering is that heating by immersion heater is close to 100% efficient but a gas boiler is less so (exact losses vary for different boilers).

phsci

EricMears said:
Another point worth considering is that heating by immersion heater is close to 100% efficient but a gas boiler is less so (exact losses vary for different boilers).

And there are no transmission losses from the pipes connecting the boiler to the hot water storage cylinder.

silverwhistle

Interesting thread as I am in a similar position: iboost, car, GO etc.

As I type I've already put 2.55kWh into the tank today so a useful contribution. I've one of the early iboost (8633kWhs) so no timer function so in the same position as QrizB.

JimLad

silverwhistle said:

Interesting thread as I am in a similar position: iboost, car, GO etc.

As I type I've already put 2.55kWh into the tank today so a useful contribution. I've one of the early iboost (8633kWhs) so no timer function so in the same position as QrizB.

I set it up last night to boost for 1.5 hours in the go period and turned off the gas hot water! Ill let you know if i get cold showers or astronomical leccy bills!

Are you sure about the timer function? I didnt think mine did but if you hold A for 5 seconds and release and then press A to scroll though you might get to a boost timer?