Immersion Heater

[Mags22]

I have a large well lagged. Hot water cylinder, is it cheaper to leave the immersion heater switched on constant,or twice daily? I don’t use a lot of hot water,but have a bath/shower daily

[Atheist]

It seems to me that having a large volume of water kept at high temperature 24 hrs a day must be more expensive than heating it up only when necessary. I'd be interested to hear other views.

[Buenchico]

It's a MYTH that leaving an immersion heater on all day is cheaper than only turning it on when it's needed. Debunked here:
https://www.cse.org.uk/advice/advice-and-support/energy-mythbuster

[barry1010]

Mine is on for 30 minutes a day. My showers are electric so heat the water; washing machine and dishwasher are cold fill.

[Atheist]

Mags; Would you think it cheaper to leave the kettle simmering all day or just turn it on when you fancied a cup of tea? I'm sure it's cheaper to turn on the kettle when you need a cuppa. That's how I see it.

[Bert45]

I went to Buenchico's link. It just said that the common belief was not true. It did not, imo, "debunk it". The fact is that, no matter how well insulated the tank is, it will still lose heat. Some heat will actually go along the copper pipes that will carry hot water when it is needed. The heat loss is proportional to the fourth power of the absolute temperature of the hot body, so the hotter the tank, the hotter the ooutside of the insulation, the faster heat is lost. It's obvious that, when the tank has cooled down to the same temperature as the house, no further heat will be lost. If the myth were true, you would leave the immersion heater on if you went on holiday for two weeks.

[Atheist]

Bet; I agree with your conclusion, but I think that you don't take account of temperature difference between tank and its surroundings when you say "The heat loss is proportional to the fourth power of the absolute temperature of the hot body." Apart from that I agree with your analysis and conclusion. (I'm nit-picking).

[Ryzen]

If you dont use much hot water.. have an electric shower installed to heat water on demand..boil a kettle for washing up and use the immersion only when you want a bath. Dont leave it on all day it will cost you.

[Hopkirk]

Is the immersion heater the only way to heat the water?
Sometimes they are fitted as a back up to gas heating, in which case never turn it on.

[burlyshirley]

I heat my water with an immersion heater and I've heard all those comments over the years about leaving it on all day and have taken no notice whatsoever. The dial on the electric meter spins round so much faster when the immersion is on, so I only put it on when I want hot water usually for about 20 minutes a day or longer if I want a bath. Works for me !

[david small]

Leaving it on permanently will be more expensive. I’ve done both.