Hot tank with two immersion heaters

[CadenL]

Hi everyone
I have a 20 year old Megaflo CL250 indirect hot water tank that I typically heat with an oil-fired boiler. It has locations for two immersion heaters (one at the base of the tank and the other halfway up). Only the lower immersion is installed and the other (halfway up the tank) is just blanked off.
Due to the rise in oil prices (and poor availability) I'm looking to use the immersion heater to heat the water overnight using economy 7. The immersion is fitted with a timer that I can use but I've discovered the element has failed - this probably happened years ago and has gone unnoticed.
I have a suitable replacement immersion heater but can't get the old one out as it's too tight to move at the moment.

I had the idea of installing the immersion in the mid-way location (as the installed blank can be removed ok), but wanted to understand any impact of doing this. I guess I'll only be able to heat the water in the upper half of the tank which I think will be fine for me as it's a big tank and only me in the household (plus I only shower once a week......just kidding! )
Would this be a suitable option - even if just for the short-term until I can get the lower immersion to budge.

Many thanks
Caden

 

[townfanjon]

The only problem heating the top of the tank is when you draw off hot water it will be replaced by cold water which will come in the bottom of the cylinder and start to cool the top .
I used to work for Kingspan and they didnt recommend it because the cylinder was obviously at diff temps , however on an old one like yours it has no warranty issues .

 

[CadenL]

The only problem heating the top of the tank is when you draw off hot water it will be replaced by cold water which will come in the bottom of the cylinder and start to cool the top .
I used to work for Kingspan and they didnt recommend it because the cylinder was obviously at diff temps , however on an old one like yours it has no warranty issues .

Thanks for your thoughts. I kind of assumed that it will only be heating the top half anyway and the lower half would remain cold. When the cold enters the bottom of the tank it will be joining water that is already relatively cold. But isn’t that what happens anyway with just the lower immersion heater active? As hot water is drawn off it’s replaced by cold at the bottom. I guess there might be an argument to say that if 50% of the tank is always cold water then the cooling affect on the 50% that is warm will be greater?
I might just try it to see how it goes

 

[Chuck]

Repairs to this cylinder can only legitimately be done by a plumber with a G3 ticket, i.e. trained and qualified to work on unvented HW systems.

 

[Murdoch]

OP -unless you already have Economy 7, I suspect you might not save anything. Electric suppliers may reduce the cost over night but some of them also increase the daily cost too.

Do your sums carefully before making any decisions

 

[CadenL]

OP -unless you already have Economy 7, I suspect you might not save anything. Electric suppliers may reduce the cost over night but some of them also increase the daily cost too.

Do your sums carefully before making any decisions

Thanks - yes I do have E7 already. But you're right, I will need to do the sums and it's not that easy as I can't tell how much oil I use to heat the same volume of water. What I do know is that what would normally cost me £1200 to fill my oil tank would now cost me nearly £5k if I filled it today!!

 

[Murdoch]

Thanks - yes I do have E7 already. But you're right, I will need to do the sums and it's not that easy as I can't tell how much oil I use to heat the same volume of water. What I do know is that what would normally cost me £1200 to fill my oil tank would now cost me nearly £5k if I filled it today!!

so if you already have and use E7 then it makes sense to explore the costs to make the changes.