Immersion heater tank on all the time

RealGem

Hi, 

As a child in the 70s, we had an immersion heater tank and it was only ever switched on twice a day for about two hours each time. We didn't have gas central heating. But we did have some sort of old boiler with a pilot light that presumably served the cooker and the gas fire. 

When my sister flew the nest, we all laughed when we found out that she had had her immersion heater on the whole time for several months, as this was seen as a huge waste of electricity. Once she and her boyfriend turned it off for most of the day, they still had enough hot water and their electricity bills reduced by a lot. 

But recently I have met a young family who keep their immersion tank on all the time. I said it only needs to be on in the morning and night, as it has thick lagging to keep it warm. But I was told that if it is left on all the time, they will have constant hot water. To him it was a no brainer that it needs to be on constantly. But the whole house is out for at least seven hours a day.

They do have gas central heating, and a modern combi boiler, so that's different to my situation as a kid. 

Am I right in thinking it is wasteful for them to keep the tank on all the time?

I'm only trying to save them money. 

Thanks

TELLIT01

Certainly heating water when nobody is in the house all day is wasteful, but how much difference it would make is questionable if the hot water cylinder is properly insulated.

Ebe_Scrooge

I'd agree with the above - if the tank is properly insulated then it'll probably not make much of a difference.  I would question why they're using the immersion at all though, if they've got a combi boiler?  One of the big advantages of a combi is that you've got hot water on demand and only heat what you need.  And gas is a cheaper method of heating than electricity.

RealGem

Ebe_Scrooge said:

I'd agree with the above - if the tank is properly insulated then it'll probably not make much of a difference.  I would question why they're using the immersion at all though, if they've got a combi boiler?  One of the big advantages of a combi is that you've got hot water on demand and only heat what you need.  And gas is a cheaper method of heating than electricity.

Yes, I had a flat that had both and I never used the tank at all and was fine. 

I just texted them now and they laughed and said they DO turn the boiler off now in summer. (Nooo! Wrong one! ...turn the TANK off!)

The tank makes the upstairs like an oven, even with the lagging! So the insulation isn't as brilliant as it could be. 

davemorton

Curious really.  How does the system know when you turn the hot tap on, whether the hot water should come from the tank or the combi?  Never knew you could have both on the same system. 

Alanp

The immersion heater will have a thermostat and will turn off when the temperature it’s set to is reached, turning on again once it falls, so if no one is drawing off water then , providing it’s properly lagged, it shouldn’t be on all the time..

Section62

davemorton said:

Curious really.  How does the system know when you turn the hot tap on, whether the hot water should come from the tank or the combi?  Never knew you could have both on the same system. 

It doesn't know.  What typically happens is some hot taps/appliances are plumbed from the HW side of the combi, and others are plumbed from the hot water cylinder.  E.g. the kitchen hot tap could be fed by the boiler, the bathroom from the HWC.

Which is why...

RealGem said:

Ebe_Scrooge said:

I'd agree with the above - if the tank is properly insulated then it'll probably not make much of a difference.  I would question why they're using the immersion at all though, if they've got a combi boiler?  One of the big advantages of a combi is that you've got hot water on demand and only heat what you need.  And gas is a cheaper method of heating than electricity.

Yes, I had a flat that had both and I never used the tank at all and was fine. 

I just texted them now and they laughed and said they DO turn the boiler off now in summer. (Nooo! Wrong one! ...turn the TANK off!)

The tank makes the upstairs like an oven, even with the lagging! So the insulation isn't as brilliant as it could be. 

...the first BiB could be a mistake.  If the HWC is supplying some of the hot taps then it needs to be left switched on or heated by the combi, depending on how it is set up.

In your first post you said the hot water cylinder "has thick lagging" - which you'd normally expect would result in minimal heat loss, rather than causing the whole upstairs "being like an oven".  It sounds like further investigation is needed into what is causing the oven-like conditions, as it shouldn't be the HWC.

RealGem

Section62 said:

davemorton said:

Curious really.  How does the system know when you turn the hot tap on, whether the hot water should come from the tank or the combi?  Never knew you could have both on the same system. 

It doesn't know.  What typically happens is some hot taps/appliances are plumbed from the HW side of the combi, and others are plumbed from the hot water cylinder.  E.g. the kitchen hot tap could be fed by the boiler, the bathroom from the HWC.

Which is why...

RealGem said:

Ebe_Scrooge said:

I'd agree with the above - if the tank is properly insulated then it'll probably not make much of a difference.  I would question why they're using the immersion at all though, if they've got a combi boiler?  One of the big advantages of a combi is that you've got hot water on demand and only heat what you need.  And gas is a cheaper method of heating than electricity.

Yes, I had a flat that had both and I never used the tank at all and was fine. 

I just texted them now and they laughed and said they DO turn the boiler off now in summer. (Nooo! Wrong one! ...turn the TANK off!)

The tank makes the upstairs like an oven, even with the lagging! So the insulation isn't as brilliant as it could be. 

...the first BiB could be a mistake.  If the HWC is supplying some of the hot taps then it needs to be left switched on or heated by the combi, depending on how it is set up.

In your first post you said the hot water cylinder "has thick lagging" - which you'd normally expect would result in minimal heat loss, rather than causing the whole upstairs "being like an oven".  It sounds like further investigation is needed into what is causing the oven-like conditions, as it shouldn't be the HWC.

Oh OK, thanks to the first point. 


The oven conditions I suspect are due also to the temperature of the water coming from the tank. The hot water is unbelievably hot. You could not put your hand under it for half a second, so very near boiling. I think they've got the HWC thermostat on way too high.

But they don't seem too concerned with my suggestions, so I'm going to leave it. 

Thanks anyway for your help.

markin

The immersion is probably set to 75-80c if the plumber didn't think to change it.

Zandoni

It's always best to have an immersion on some sort of timer, probably a hour in the morning and the same in the evening. I'd look into having a bit of plumbing work done so that the combi heats all the taps in the house.

Section62

Zandoni said:

I'd look into having a bit of plumbing work done so that the combi heats all the taps in the house.

I think that would depend on the mains water pressure and flow - it could be the HWC was retained with a gravity system in parts of the house because the mains supply is inadequate.

Alternatively, there could be cases where the appliance and the boiler are so far apart that it takes an excessive time (+water volume) for hot water to come through, so a 'local' supply of stored hot water could be used to overcome that inconvenience (and possible inefficiency).