Electric Immersion Heater Options

Stubod

If the hot water tank is used to feed a power shower it will be quite large? May be better to get a self heating shower and replace the hot water tank with a more modern (ie better insulated), smaller one?

doodling

Hi,

Apodemus said:

While all electric heaters are indeed equally efficient in terms of energy in/energy out, the heat transfer to the water in the tank may be affected by lime-scale on the element, meaning that it will take longer for the tank to come up to temperature.  Also, both time taken and total energy used will vary with the size of the tank.

So it is quite possible that the OP simply has a large tank, a scaled-up element, compounds this with heat loss from tank & pipes and then adds a once-a-day water-heating regime which means that they are always starting from the coolest possible water in the tank.

In general, for an immersion heater, limescale will not significantly reduce the power transferred to the water as the electric element will simply run hotter to compensate (at the cost of a reduced life).

If well insulated then neither the size of the tank, nor how often it is heated will have a significant effect on the amount of energy used.  The key factor will be the amount of hot water actually used.

Of course, many tanks are not as well insulated as they could be.  The OP needs to spend some time making sure that the whole tank and any connecting pipework is really well insulated - if the tank cupboard is warmer than the rest of the property then the tank doesn't have enough insulation.

doodling

Hi,

Stubod said:

If the hot water tank is used to feed a power shower it will be quite large? May be better to get a self heating shower and replace the hot water tank with a more modern (ie better insulated), smaller one?

The right solution for the OP depends on the selection of the right electricity tariff.

The flat is all electric so ideally it would be heated with a heat pump system of some sort and in that case you would expect the hot water to be most cost effectively heated by the heat pump.  Such a configuration remains relatively rare however.

The next most cost effective heating arrangement would be the use of storage heaters on economy 7, with hot water also heated at cheap rate. In that case it is probably cheaper to accept the small heat loss from the tank as the overall cost will still be cheaper than an electric shower at daytime rates.

Only if the heating uses non-storage heaters at normal rates (at vast expense!) is an electric shower likely to be a cost effective solution.

Jonboy_1984

This echoes my experiences of a 25 year old scaled up tank in a hard water area.

Having replaced elements 4 times in two years as they died, it developed a leak on the drain valve and was replaced. New tank took less than half the time to heat to the same level (unit of measure used being hot enough for the wife to enjoy a bath…!).

MattMattMattUK

Jonboy_1984 said:

This echoes my experiences of a 25 year old scaled up tank in a hard water area.

Having replaced elements 4 times in two years as they died, it developed a leak on the drain valve and was replaced. New tank took less than half the time to heat to the same level (unit of measure used being hot enough for the wife to enjoy a bath…!).

When the old tank was replaced in my mum's house 15 years ago it took three of us just to be able to carry it down the stairs, when the plumber split it open on the lawn he showed me how full of limescale it was, more than half the capacity of the tank was taken up with limescale, needless to say my mum then decided to have the water softener fitted!

littleteapot

Mstty said:

Scary calculator alert, if you know your tank size and element kWh then have a dabble

https://www.sust-it.net/immersion-heater-energy-calculator.php

With EDF's current £0.07 night rate currently in eastern region, that makes it cost £0.44 to heat our 120 litre tank from cold each night. This calculator is a bit limited though as it doesn't let you set the temperature it is heated to. Ours is a sealed mains-pressure system so only heated to 50c as there's no possibility of legionella entering the system.

EDF's E7 EPG tariff has been our only saving grace this winter with decent storage heaters, as having an infant and toddler in the house almost 24/7 means we can't safely have the room temperatures very low. 16-18c is what we try to maintain.

Mstty

littleteapot said:

Mstty said:

Scary calculator alert, if you know your tank size and element kWh then have a dabble

https://www.sust-it.net/immersion-heater-energy-calculator.php

With EDF's current £0.07 night rate currently in eastern region, that makes it cost £0.44 to heat our 120 litre tank from cold each night. This calculator is a bit limited though as it doesn't let you set the temperature it is heated to. Ours is a sealed mains-pressure system so only heated to 50c as there's no possibility of legionella entering the system.

EDF's E7 EPG tariff has been our only saving grace this winter with decent storage heaters, as having an infant and toddler in the house almost 24/7 means we can't safely have the room temperatures very low. 16-18c is what we try to maintain.

Ah the famous eastern region E7 EDF rate. Nice work.

Ectophile

If it's a bare copper tank, find the thickest insulating jacket you can, or replace it.  Modern tanks come with a thick layer of foam insulation all over and will stay hot all day once heated up.

littleteapot

Mstty said:

littleteapot said:

Mstty said:

Scary calculator alert, if you know your tank size and element kWh then have a dabble

https://www.sust-it.net/immersion-heater-energy-calculator.php

With EDF's current £0.07 night rate currently in eastern region, that makes it cost £0.44 to heat our 120 litre tank from cold each night. This calculator is a bit limited though as it doesn't let you set the temperature it is heated to. Ours is a sealed mains-pressure system so only heated to 50c as there's no possibility of legionella entering the system.

EDF's E7 EPG tariff has been our only saving grace this winter with decent storage heaters, as having an infant and toddler in the house almost 24/7 means we can't safely have the room temperatures very low. 16-18c is what we try to maintain.

Ah the famous eastern region E7 EDF rate. Nice work.

If we were on smart prepay it would be £0.0094 per kWh, effectively free. But I know this is just an anomaly of the way EDF are applying the EPG and won't be the norm, so i'll stick with DD. ~90% of our usage is off peak at the moment. Like you we have been a little bit lax because of this rate and will certainly try harder next winter to cut consumption. As the children get older and youngest wont be crawling around the floors we can turn off heating in kitchen and bathroom next winter.

Can then just rely on the dehumidifiers to prevent damp and mould in those rooms.

learner21

I have a 120 litre tank - which is well insulated - I also had a leaking drain valve at bottom of tank - so now I have 2 valves.
I cannot post links yet - but fitted a new immersion heater - a Tesla T-Smart Immersion Heater which I control with an app, but most importantly lets me see the tank temperature on my phone. I would say takes 30 minutes to heat to 55degC. 
The fitted immersion is also unlikely to have a faulty thermostat - which means it's on all the time - as the water would be hot all the time.