Immersion Heater help

rachaelsmith82

Hi All, 

I am looking for some advice in regards to my Immersion heater. I live in an electric only flat and have Economy 7. I have an immersion heater that comes on at midnight for cheaper rates. My query is - from my research it seems immersion heater heats up then stops at desired temp and keeps water hot for me that day. So this maybe a stupid question but if I try to use less water ( never had an issue with running out of hot water ) to save money is there any point as Immersion heater will just go through the same process the next night? 

Just wondered if I used half the hot water say - would the following night it require less to heat up or would it have cooled down anyway meaning there was no point in trying to use less? Also would it help to set timer for 5.30am etc so closer to time I use it?

Apologies - this stuff really confuses me! 

Thanks in advance

Ultrasonic

First off using less water will save you money on your water bills, assuming you have a metered supply.

I think using less hot water will also save you electricity for the reason you say - the water will start off warmer the following night and so take less energy to heat up again.

[Deleted User]

Hi,

though why have it on at midnight, if you're up at 6 or 7 all you need is a couple of hours of the cheap rate before you get up.

ProDave

As you use hot water there is left hot left in your tank.

At night when the heater comes on it heats the tank until the whole tank is up to temperature.  So if you have drawn less hot water out, then there will be less heat to put back so the immersion heater will run for less time. So it will save you money.

You might want to think about fitting an immersion heater timer.  At the moment the immersion probably comes on at about midnight and stays powered until about 7AM.  The tank will be fully heated withing the first 2 hours of that.  So fitting a timer so the immersion does not come on until say 5AM would mean it still heats on the cheap rate, but has less time it needs to store that hot water befroe use.

lohr500

How well insulated is your hot water cylinder?
Is it a modern style one with solid insulation around it, or an older one with a loose fitting jacket? Does the outer surface of the insulation or jacket feel warm to the touch?

The key is to make sure the tank is retaining as much heat as possible once the water has been heated up.

As you have figured out, once the water reaches the temperature on the immersion heater thermostat, the thermostat will switch off the heater and only switch it back on as the water cools down.

A few things to consider/check : 

Make sure the heater timer is set to the correct time and that it is only switching on the heater during your Economy 7 hours. Economy 7 times vary by region so you need to check the times for your region. Your electricity supplier should be able to tell you this. Also, check to see if the Economy 7 hours change when the clocks change and if your timer also adjusts for the clock change. It is really important to make sure your timer aligns with the Economy 7 times, otherwise you risk using peak rate electricity to heat the water  

If the insulation around the tank is poor, consider adding an additional jacket on top of any existing insulation, or replace the existing jacket with a thicker one if the jacket is a loose fitting type.

If your hot water is above 60 deg C, consider getting the thermostat setting reduced to 60 C. If you aren't using the full tank each day and the water is above 60 C, you could save money by heating it to a lower temperature. Keep it at 60 minimum though to minimise the risk of legionella bacteria developing.

With a well insulated tank, I am not sure about the benefit of setting the timer to come on at 5:30am instead of midnight. Probably arguments for and against. I think the bigger savings will come from the suggestions/checks I have listed above.

coffeehound

[Deleted User] said:

 if you're up at 6 or 7 all you need is a couple of hours of the cheap rate before you get up.

ProDave said:

So fitting a timer so the immersion does not come on until say 5AM would mean it still heats on the cheap rate, but has less time it needs to store that hot water befroe use.

lohr500 said:

With a well insulated tank, I am not sure about the benefit of setting the timer to come on at 5:30am instead of midnight. Probably arguments for and against. I think the bigger savings will come from the suggestions/checks I have listed above.

It probably wouldn't have been worth the outlay in the recent past, but with prices heading as they are it is starting to make financial sense to install something to achieve this.  

I don't know what E7 rates are like now, but say they end up at 25p per unit off-peak.  If a hot water tank + pipwork loses 2 kWh per 24 hours when at full temperature, then by putting back the heating time by 5 hours you could save

5 x (2/24) x 365 days x £0.25 = £38 a year

I was thinking the ideal thing to do this would be a delay-on timer relay.  When powered on, they wait for the set time period to elapse before switching on the load.  No clock to keep synchronised, and it would adjust automatically to any changes such as BST/GMT.

One like this would suit:  https://www.ebay.co.uk/itm/402590859796


It can switch 16 amps so fine for an IH.  Install it in a £5 DIN-rail box with a couple of compression glands after the isolator switch in the airing cupboard.  Set the time delay to 5 hours.  Total outlay about £25 for hardware, so might break even within a year depending on installation cost.

Gerry1

lohr500 said:

Make sure the heater timer is set to the correct time and that it is only switching on the heater during your Economy 7 hours. Economy 7 times vary by region so you need to check the times for your region. Your electricity supplier should be able to tell you this.

It's not the supplier that determines the times, it's the DNO.  But even then, they can only tell you what the times ought to be, not the times when your meter actually switches over.  If for any reason there's a variance then you pay the price.

There's only one way to be sure and that's to look at your meter and see when the E7 period starts and finishes.  Remember that in some areas there's a two hour interlude at day rate.

You can find out the likely times here.  The Area number can be found by looking at the two digits on the left of the lower row of your S number shown on your bill.  It's 13 (Merseyside and North Wales) in this example.

Gerry1

coffeehound said:

[Deleted User] said:

 if you're up at 6 or 7 all you need is a couple of hours of the cheap rate before you get up.

ProDave said:

So fitting a timer so the immersion does not come on until say 5AM would mean it still heats on the cheap rate, but has less time it needs to store that hot water befroe use.

lohr500 said:

With a well insulated tank, I am not sure about the benefit of setting the timer to come on at 5:30am instead of midnight. Probably arguments for and against. I think the bigger savings will come from the suggestions/checks I have listed above.

I was thinking the ideal thing to do this would be a delay-on timer relay.  When powered on, they wait for the set time period to elapse before switching on the load.  No clock to keep synchronised, and it would adjust automatically to any changes such as BST/GMT.

One like this would suit:  https://www.ebay.co.uk/itm/402590859796


It can switch 16 amps so fine for an IH.  Install it in a £5 DIN-rail box with a couple of compression glands after the isolator switch in the airing cupboard.  Set the time delay to 5 hours.  Total outlay about £25 for hardware, so might break even within a year depending on installation cost.

Unfortunately that idea might go seriously pear shaped if your E7 times are 2230 - 0030 and 0230 - 0730 !

coffeehound

^ In that case, Gerry1, you just set the delay to 3 hours

cx6

when the heater comes on at midnight it heats the water - a lot if water - to the set temperature.

For the rest if the night the heater will come on and off to maintain that temperature as heat is lost and the water cools

This is wasteful as you are simply paying to heat the airing cupboard

Get a timer and set  it to come on about an hour before you have a shower or whatever and then turn off again

or simply switch the immersion off manually and only on an hour or so before you need hot water.

If you need a little bit of hot water use the kettle.

QrizB

cx6 said:

This is wasteful as you are simply paying to heat the airing cupboard

It's probably worth getting a bit of perspective on the amount of energy lost.

A tank that's been manufactured and lagged to relatively recent standards woll lose heat at around 60 watts. Over 7 hours that's 0.42kWh, and that's only really "wasted" for the half of the year where you're not using E7 to heat your home.

Call it 80kWh/yr, about £15/yr on a typical from-April E7 night rate.