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Immersion heater timer


blackrose

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I'm on shore power and I was thinking of fitting an immersion heater timer so that I could set it to come on twice a day for a couple of hours.

A neighbour of mine reckons it won't make much difference in terms of cost if I just left the immersion on all the time, his rationale being that it takes a lot of energy to heat the calorifier up from cold and probably not much less to put some extra lagging on it and just keep it hot all the time.

 

I would try to 'run the math' myself, but I have no idea how much heat is lost through the 40mm PU insulation on my calorifier, so I don't know how often the thermostat kicks in and switches it on if it's left on all the time.

 

Anyone know if it's worth fitting a timer?

Edited by blackrose
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If you've got a proper tank thermostat rather than just the internal cut-out stat of the heater it makes a considerable difference. I don't use an immersion, don't have the maths, but find I've still got piping hot water a day after switching off the boiler and/or engine so think the insulation is pretty good.

My two-penny worth, fit a timer if you've no tank stat or your insulation is iffy.

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I'm on shore power and I was thinking of fitting an immersion heater timer so that I could set it to come on twice a day for a couple of hours.

A neighbour of mine reckons it won't make much difference in terms of cost if I just left the immersion on all the time, his rationale being that it takes a lot of energy to heat the calorifier up from cold and probably not much less to put some extra lagging on it and just keep it hot all the time.

 

I would try to 'run the math' myself, but I have no idea how much heat is lost through the 40mm PU insulation on my calorifier, so I don't know how often the thermostat kicks in and switches it on if it's left on all the time.

 

Anyone know if it's worth fitting a timer?

 

I did measurements before and after fitting mine (coz I'm sad like that).

 

Both my calorifiers are extremely well insulated and the pipes are arranged with dips so that there is very little heat loss. To give an idea, I had just cruised all day on thursday and had both tanks at just under 70 degrees C. Then we had to leave the boat on the cut due to a family problem. When I got back on saturday morning both tanks were still above 60 degrees.

 

Fitting the timer made almost no difference to electricty consumption! The difference was there, but it was so minimal that I would have to live to a very old age in order for it to pay for the timer. But I have it now so it might as well stay there.

 

If you do go for one make sure you get one that has batteries in it otherwise it loses the time everytime you lose shorepower which soon becomes very tiresome.

 

Gibbo

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I'm on shore power and I was thinking of fitting an immersion heater timer so that I could set it to come on twice a day for a couple of hours.

A neighbour of mine reckons it won't make much difference in terms of cost if I just left the immersion on all the time, his rationale being that it takes a lot of energy to heat the calorifier up from cold and probably not much less to put some extra lagging on it and just keep it hot all the time.

 

I would try to 'run the math' myself, but I have no idea how much heat is lost through the 40mm PU insulation on my calorifier, so I don't know how often the thermostat kicks in and switches it on if it's left on all the time.

 

Anyone know if it's worth fitting a timer?

 

 

In theory if you wanted to always take out water at the same temperature then it would not make a difference of fitting a timer or not.

 

Would be a good idea any way to put some extra lagging to stop losses which is a simple way of saving a few pence.

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I think your neighbour's theory is right - water is very expensive to heat (specific heat capacity), but relatively cheap to maintain at a temperature. Leaving it on all the time might cost a little more but you can offset that with the benefits; hot water at any time, something to keep the boat slightly warm, and possibly less likelihood of ruptured joints from constant heating and cooling.

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The additional cost of leaving the immersion heater switch ON all the time is that you don't need to hold the water permanently at 65degC. It can cool to 40degC and that will still be hand-hot. If you are using a lot of water (because there is more than one person) then holding the water at 65degC has benefits because you can dilute it down to 40degC for actual use, so the hot water goes much further.

 

Chris

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It sounds like I should buy a water jacket instead of an immersion timer. Or perhaps both...

 

My immersion is set at about 55 deg C. If we assume that when the immersion is switched off it loses about 1 deg C/hour (and that's the main assumption), and during the course of a day the immersion comes on twice for 2 hours each time, this means it will lose about 10 degrees C between each time it comes on - that's 20 degrees C it will have to be raised each day in total.

 

If on the other hand the immersion is left on 24 hours/day then it will still have to make up for the losses (1 deg C/hour) - and that's 24 degrees C.

 

So by that calculation leaving the immersion on costs slightly more - unless of course the calculation is not as straightforward as that?

 

In both examples I have ignored hot water usage as this is the same in both cases.

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It sounds like I should buy a water jacket instead of an immersion timer. Or perhaps both...

 

My immersion is set at about 55 deg C. If we assume that when the immersion is switched off it loses about 1 deg C/hour (and that's the main assumption), and during the course of a day the immersion comes on twice for 2 hours each time, this means it will lose about 10 degrees C between each time it comes on - that's 20 degrees C it will have to be raised each day in total.

 

If on the other hand the immersion is left on 24 hours/day then it will still have to make up for the losses (1 deg C/hour) - and that's 24 degrees C.

 

So by that calculation leaving the immersion on costs slightly more - unless of course the calculation is not as straightforward as that?

 

In both examples I have ignored hot water usage as this is the same in both cases.

The thermostat in your immersion heater won't be sensitive enough to detect a 1degC drop in temperature. They have built-in "hysteresis" with around a 5-7degC temperature difference between switch ON and switch OFF. This is to prevent the thermostat's continuously clicking ON and OFF all the time which would severely limit its longevity.

 

Chris

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I would try to 'run the math' myself, but I have no idea how much heat is lost through the 40mm PU insulation on my calorifier, so I don't know how often the thermostat kicks in and switches it on if it's left on all the time.

 

Get one of these Energy Monitors ( http://www.maplin.co.uk/Module.aspx?Module...O&U=strat15 ) and do yourself some tests too see.

 

I did the same and found that via timer / manual rather than leaving on all the time is a lot cheaper, but I'm only heating up 10ltr which doesn't take long to heat from cold, if I was heating up a large amount I think it would be a closer result that it would be worth leaving on.

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