Electric Immersion Heater Options

yakuzakitty

Recently moved into a flat, and discovered rather a relic of an immersion heater and tank. Our flat is all electric, no gas.

It’s pretty inefficient and is taking upwards of 1.5hrs to get water hot enough to shower in - which is costing us a lot. 

Apart from getting a new immersion heater and tank installed (which as far as I can tell probably won’t be much better at a cost of £2k), or getting a jacket which will only help keep the water hot, does anyone have any suggestions?

Mstty

How much is a lot to you in kWh for 1.5 hours heating of the hot water tank?

yakuzakitty

Mstty said:

How much is a lot to you in kWh for 1.5 hours heating of the hot water tank?

Difficult to say in kWh, but it’s costing us about £5 every time we want to have a shower.

Raxiel

All electric heating elements are 100% efficient, a new one won't heat the water any cheaper. A new tank might have better insulation to keep the heat in, but likewise you may be able to just buy a jacket to go around it as you suggest.

When I had an all electric flat, the tank had two immersion heaters, one at the bottom intended to heat the tank overnight on E7 off peak rates, and one about half way off for an 'on peak boost' that could top it off if I needed extra hot water during the day.

So the first suggestion would be to find out if your on Economy 7, and if so make sure you heat the tank overnight, you may have to heat it for longer, but it should be cheaper too.

It's possible that the current heater (or one of them if there's two) has just had it of course and isn't heating up as quickly as it should, in which case you could probably get just the heating element changed rather than the whole tank, but electricity in = heat out, so anything that means it heats up faster will also mean it spins the meter faster too.

Stubod

..could you not fit an "instant" shower....ie one that heats the water as you use it?

[Deleted User]

yakuzakitty said:

Recently moved into a flat, and discovered rather a relic of an immersion heater and tank. Our flat is all electric, no gas.

It’s pretty inefficient and is taking upwards of 1.5hrs to get water hot enough to shower in - which is costing us a lot. 

Apart from getting a new immersion heater and tank installed (which as far as I can tell probably won’t be much better at a cost of £2k), or getting a jacket which will only help keep the water hot, does anyone have any suggestions?

Electricity is 100% efficient. Assuming you have a 3kW immersion heater then 4.5kWh is not excessive energy usage. Clearly, the cylinder needs to be properly insulated to retain the heat that the immersion heater has put into the hot water cylinder. Another challenge with domestic hot water systems is often the distance between the cylinder and the tap/shower: these pipes are rarely insulated. The heat is not lost it just contributes to heat going into the room.

Raxiel

Stubod said:

..could you not fit an "instant" shower....ie one that heats the water as you use it?

That would be a little cheaper than heating water in a tank at flat or peak rate electric and then piping it to the shower, but more expensive than heating it in a tank with off-peak electric.

Mstty

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

Reed_Richards

yakuzakitty said:

Mstty said:

How much is a lot to you in kWh for 1.5 hours heating of the hot water tank?

Difficult to say in kWh, but it’s costing us about £5 every time we want to have a shower.

A typical immersion heater uses 3 kW.  So 3 kW for 1.5 hours is 4.5 kWh.  At the current SVT a kWh of electricity costs about 35p so I would expect the cost of a shower to be no more than £1.60.  If it actually costs you £5 then either you are being massively overcharged for your electricity or you have a highly unusual high-power immersion heater and you take very long showers that use 14 kWh worth of heat.  It doesn't really add up.  

RedFraggle

Is it a power shower i.e. one with an additional pump? That would add to costs but still not that much. 
Is the tank insulated?

Apodemus

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.