Standby usage of electric hot water tank

BoyJohn811

Hi, I was wondering if someone could help me. I rent a one bedroom flat with only electricity as fuel. I am often away for a couple of days and I have noticed that my electricity usage is fairly high even when I am not in. When away, I literally have only two items running (I unplug everything else), a small underbench fridge/freezer (fairly new and efficient) and an older, large electric heater for hot water only (heating of the flat is with storage heaters that are off). With these two items only, my smart meter shows up to £1.5 per day, which I find a bit high (I am on Octopus tariff with 46.89p/day standing charge). It means that I pay ~£45 per month even if I am not at home at all. I do not think it is my fridge, I suspect it is the hot water tank. I appreciate that electricity consumption can depend on a million things (age, water tank size, limescale inside, etc.); however, I was just wondering if this kind of standby usage sounds OKish to someone smarter than me.

Thank you very much.

Swipe

Is there not a switch to turn off the water heater while you are away?

Gerry1

A modern well insulated hot water tank leaks about 1.8kWh per day.  Assuming you meant £1.50 per day and ignoring the fridge/freezer that equals a leakage of about 3kWh per day which is probably correct for an old tank.

Just switch off the immersion heater(s) when you go away.

Reed_Richards

A small fridge could consume somewhere between 50 W and 100 W on average.  So that would be somewhere between 1.2 kWh per day and 2.4 kWh per day.  Add that to @Gerry1 's 1.8 kW h per day for the immersion heater and your in the ballpark of your £1 per day plus standing charge.  

lohr500

You could also look at the level of thermal insulation around the tank.

An extra thermal jacket would cost around £20 from somewhere like B&Q or Screwfix. It would help irrespective of if you turned the immersion off when away or if you left it switched on.
Check also to see if the hot water pipe leaving the immersion heater is lagged or not.

It is all about conserving the heat in the tank and pipework.

The only downside would be if you use the cupboard where the immersion tank is located for airing towels, etc. It will be cooler with extra lagging on the tank and pipes.

BoyJohn811

Thank you all for the clarification and suggestions. Unfotunately, turning it off for a day or two is not an option as I will need it when I am back, but will look into what I could possibly improve. Thanks again.

Reed_Richards

You could fit a timer.  My immersion heater is controlled by a WiFi switch which (as I have a WiFi router) means I can turn it on from anywhere with internet or a mobile signal using my phone.  The switch cost approximately £50 so it would not take too many days away to pay for itself.  

Alnat1

How long does your tank take to heat up enough for a bath/shower?

We only heat ours for 40 minutes a day, gives enough hot water for a couple of showers with some left over. This uses around 3.5kWh in summer, around 5kWh in winter (water temp set higher) I would never leave it heating 24/7. If we're away, it's switched off, as we know we can heat it up as soon as we get home and have showers within an hour.

macman

As above: 30 mins heat on your return should be enough to bring it back up to temp again, so I don't understand why you can't turn it off?

Reed_Richards

Alnat1 said:

If we're away, it's switched off, as we know we can heat it up as soon as we get home and have showers within an hour.

macman said:

As above: 30 mins heat on your return should be enough to bring it back up to temp again, so I don't understand why you can't turn it off?

If it's been off for a while the water inside will be a lot cooler than if you just replenish the hot water you use each day;  "showers within an hour" implies warm water and the time it takes to get from cold to warm will depend on the volume of the tank as most heat at 3 kW.    

TheElectricCow

Reed_Richards said:

Alnat1 said:

If we're away, it's switched off, as we know we can heat it up as soon as we get home and have showers within an hour.

macman said:

As above: 30 mins heat on your return should be enough to bring it back up to temp again, so I don't understand why you can't turn it off?

If it's been off for a while the water inside will be a lot cooler than if you just replenish the hot water you use each day;  "showers within an hour" implies warm water and the time it takes to get from cold to warm will depend on the volume of the tank as most heat at 3 kW.    

In my experience 30 minutes heating from cold is plenty enough to bring the tank output to a warm enough temperature for a single shower. When heating, the warm water rises to the top of the tank and is drawn off first, so it’s not strictly necessary for the entire tank to reach temperature before an amount of suitably hot water is ready for use (which could well be within 20 minutes assuming the water coming in isn’t too cold).