question regarding length of immersion heater


Postby djhollowman » Wed Jan 16, 2008 9:14 pm

Hi all!
Hoping someone can help a noob please!
Although I have an immersion heater in the top of my hot water tank, up to now I have not been using it to heat my water. My central heating system does both central heating and hot water, and it runs on oil fed into a burner. The price of this domestic heating oil is rising so fast that I'm considering using the immersion to heat my water, thus enabling me to not use the oil at all during the (supposedly!) warmer months ahead.
However:
The immersion heater in my hot water tank is dead (definately dead, tested across the terminals) It was a Backer BT7 model.
Upon taking it out of the copper tube I find it's only 7" long. The copper tube is also about this length - I checked how deep it went into the tank with a rod and it's about 7" as well.
I would have expected it to be longer than that. The tank is about 3 feet high and 5 feet around. Am I right in thinking that this immersion (if it was working) would only heat the top 7" of the water in the tank??
Should I get a [i]longer[/i] immersion fitted?
I have to replace the immersion anyway, so obviously this would be the ideal time to install a longer one if that proved necessary/beneficial.
Having never relied upon the immersion before, I want to try and understand the situation before buying any new parts.
The house was a new build about 7 years ago.
Really appreciate any help with this!
Thanks.
DJ
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Postby marrtin » Thu Jan 17, 2008 10:13 pm

Are you sure you have removed the immersion heater? By your description it sounds like just the thermostat. You would have to drain down and remove the whole assembly in the tank to access the element?
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Postby frogger » Thu Jan 17, 2008 10:40 pm

you will need a 27" imersion
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Postby djhollowman » Fri Jan 18, 2008 8:07 am

[quote="marrtin"]Are you sure you have removed the immersion heater? By your description it sounds like just the thermostat. You would have to drain down and remove the whole assembly in the tank to access the element?[/quote]
I think you're right! I've only removed the 'stat. But even so, shouldn't it be longer for this size of tank?
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Postby djhollowman » Fri Jan 18, 2008 8:08 am

[quote="frogger"]you will need a 27" imersion[/quote]
That's what I'm thinking!

Thanks
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Postby marrtin » Fri Jan 18, 2008 4:32 pm

Immersions come in two sizes 11" or 21" so by the length of the thermostat, I would suggest you have the 11" version which will only heat a bowl full of water.

Assuming the electrical suplly will cope with the 3kw type replace the 11" with a 21".

But hang on a moment - how exactly did you arrive at the conclusion that the element was faulty?
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