Yearly kWh for an average flat / immersion heater expense

PJ2000

I've just checked our 2 person flat's electricity usage and found it to be about 4750 kWh per year / 13kwh per day. All the average figures I've found online seem to indicate this is deemed more extreme than the usage of a very large house of 4 people. Apparently the yearly figure should be closer to 2000 kWh per year.
Other than fairly standard efficient usage, we have a water pump which doesn't seem a massive issue despite helping the water flow for showers and use of the bathroom taps. We also have an old economy 7 dimplex storage heater which isn't much use - so we only very occasionally warm a room we're in with a freestanding electricity heater - we are very wary of using it as we fully understand the added expense of using it at the more expensive rate.
So the main culprit for our high figures seems to be our overnight immersion heater which is triggered by the economy 7 at night. In the mornings I can see that its effect has already racked up about a third or more of our general electricity usage overnight. The water is always VERY hot and never runs out. I would like to turn it down - but on opening up the panel with the temperature gauge it seems set to the lowest setting - from memory it was 50 degrees. Does it sound like I need to replace the unit? I'd rather not have to remember to turn it on and off on certain days if possible - but I can't see any other way of cutting the cost and the heat of the water. Or is there a workaround/cut off I don't know about. Any thoughts would be great. Thanks

Rodders53

Get a waterproof thermometer to measure the HW temperature from the nearest tap to the tank (I use an electronic meat thermometer)...  Only then will you know the temperature set.  Actually rotate the knob on the thermostat to check that it aligns with the numbers and isn't indicating a wrong lower temperature?  A broken thermostat might nearly boil the water (but there should be an overheat cutout).

Tank size in litres?  (Or make and model if that is shown on a label).  Vented (cold water tank above the HW tank) or unvented (with an air bubble or white expansion vessel and controls including a tundish).  How well insulated is it.

With no water used my 210 litre unvented well insulated tank needs a daily 2kWh (2 units) of energy input just to maintain the set temperature.  To reheat the tank after using a good amount takes 3 hours with the 3kW immersion so that's 9 kWh (units) of electric.  Your numbers will be different but should be calculatable from the manufacturers data.

You can buy immersion heater timer-controls to reduce the time it's on if desired.  Only really useful if the thermostat is broken to limit the ON time.

Mark_d

It's two of us in a 2 bedroom flat.  We use 5000kWh elec and 9000kWh gas per year.  Based on this you consumption doesn't sound unreasonable - especially given that you have electric heating.

bob2302

PJ2000 said:

I've just checked our 2 person flat's electricity usage and found it to be about 4750 kWh per year / 13kwh per day. All the average figures I've found online seem to indicate this is deemed more extreme than the usage of a very large house of 4 people. Apparently the yearly figure should be closer to 2000 kWh per year.

It doesn't seem extreme for a home with an immersion heater and electric heating. 2000 kWh per year is likely dominated by homes with gas heating and hot water.  

EssexHebridean

Don't worry about the electricity figure being higher than you have seen for "typical households" either - those figures are aimed at households where the heating and hot water is done using gas. here are separate figures for electric only households, and your use isn't at all high for that style of household!

The main thing with the immersion is that you make sure it only "kicks in" and heats on the cheap rate overnight - do you have a timer for it, or is it wired in so that it only gets a live feed at the off peak times? Also making sure it's well insulated can lower costs a fair bit as that means it retains more of the heat. 

debitcardmayhem

I would think that if you only use 1/3rd of your electricity on off peak then you shouldn’t be on economy 7?

Newbie_John

In my opinion that's a very low usage.
What's your daily consumption on summer day? Immersion heater will use about 6kWh a day, so half of your daily usage - then heating and everything else.

Also to avoid any potential legionella it's worth keeping it to 60°C, the gain of taking it down to 50°C is quite low cost wise unless you happy to do 6 days a week at 50°C and one at 60°C etc.

Scot_39

PJ2000 said:

I've just checked our 2 person flat's electricity usage and found it to be about 4750 kWh per year / 13kwh per day. All the average figures I've found online seem to indicate this is deemed more extreme than the usage of a very large house of 4 people. Apparently the yearly figure should be closer to 2000 kWh per year.
Other than fairly standard efficient usage, we have a water pump which doesn't seem a massive issue despite helping the water flow for showers and use of the bathroom taps. We also have an old economy 7 dimplex storage heater which isn't much use - so we only very occasionally warm a room we're in with a freestanding electricity heater - we are very wary of using it as we fully understand the added expense of using it at the more expensive rate.
So the main culprit for our high figures seems to be our overnight immersion heater which is triggered by the economy 7 at night. In the mornings I can see that its effect has already racked up about a third or more of our general electricity usage overnight. The water is always VERY hot and never runs out. I would like to turn it down - but on opening up the panel with the temperature gauge it seems set to the lowest setting - from memory it was 50 degrees. Does it sound like I need to replace the unit? I'd rather not have to remember to turn it on and off on certain days if possible - but I can't see any other way of cutting the cost and the heat of the water. Or is there a workaround/cut off I don't know about. Any thoughts would be great. Thanks

Firstly - you may be confusing homes with electric only - and homes with gas and electric.

The current median TDCV for electric homes is 3900 kWh (or to be more accurate those with profile class 2 multirate metering - that even Ofgem dont know if may have oil, lpg or wood burning for heating too).

And the current median TDCV for a different set of homes (and it's important to remember that) is 2700 kWh electric and 11500 kWh gas - so 14,200 kWh total energy.  Ofgem guestimate thats typically 2-3 in a 2-3 bed home.

There is an even higher Ofgem dual fuel cap for a 4-5 bed home iirc -  c4300 kWh electric + 17000kWh gas.

But these are just filtered data set quartiles - median 50% above 50% below - as a guide.  You are very unlikely to heat, wash, cook etc exactly the same as your nighbour in a fairly identical house.

And 2 cannot quite live as cheaply as one - cooking washing etc.

And as to the third comment - 13/3 - say 4.2kWh of energy would lift around 90l of water from 10-50C - my 2 bed terrace but with a cold fed electric shower - has a small tank - just over 100l.

Secondly - power (pumped) showers almost certainly use more hot water than conventional types - and the more hot water you use the more it will cost to heat.

Thirdly - Renting or owning - and type of tank and 50C

50C is too low for a tank to comply with HSE guidelines on legionella - so if you are renting - it likely invalidates any landlords legionella certification.

It's probably not too bad - but if you need a pump for your shower - it may be a vented gravity fed tank so more at risk of contamination.

I wouldn't go below 55C if loft tank vented / fed hw cylinder.

Fourth 50C itself - if at tap

50C is actually very hot - scaldingly hot in fact - which is why NHS and care homes use TMV to reduce to iirc c43C max and modern bathroom installs use TMVs domestically to reduce to 48C max before bath taps.

You could use a meat thermometer - but it's probably not that far off if uncomfortable to leave your hand under a running tap.

PJ2000

Thanks for the feedback - I'll look at the immersion following the really helpful comments - it's good to hear that it isn't necessarily an incredibly high amount though after taking into account our set up...

EssexHebridean

I don’t think the OP has a “power shower” - my impression is that they have the same set up we used to have - with an inline twin impeller pump just to give them a decent pressure for the non mains fed taps. Ours didn’t even feed the shower in fact as that was mains fed, and our actual mains pressure was fantastic, it was just anything from the tank or the immersion was a problem. 

Scot_39

Oh and one further point - if your not actually using the storage heater - but plug in's

is your off peak consumption - as a fraction of total - actually enough to justify paying day peak rate on the rest.

You say about third - which might be enough or close enough not to warrant changing - but you might want to compare vs SR deal.

And have you thought of maybe using the NSH to keep the real chill away - if just to hold a minimum temp level - and then boost above to comfort levels with plug ins as and when in room.