Away for a week, hot water on or off?

martinsurrey

lstar337 wrote: »

Only 4kWh to heat it from 18c to 58c?

yes, that part is a fact, only increased by the energy loss through the tank as it heats (an electrical element is 100% efficient)

lstar337 wrote: »

That's scary, why is it taking almost that to keep it ticking over when we use hardly any hot water at all?

poorly designed or insulated system? if the tank is poorly insulated you could easily lose a lot of heat by keeping the tank at 60degrees.

lstar337 wrote: »

Night stores are off, so I may have to investigate where that power is going.

sounds like a good idea. Turn the heater off tonight and see how much energy you use on other things.

I see we cross posted, and it looks like it is the age of the tank, and system...

macman

'Heating it up from cold' is a complete red herring! All the time it's on it will lose heat (though not much) and require more energy input.
Do you keep your kettle just below boiling i24/7 n order to 'save' the cost of heating it from cold?
Would you leave it on when away for one day? One week? One month? Where is your theoretical break-even point?
If you run it 24/7 when at home, you are just wasting money.

lstar337

macman wrote: »

If you run it 24/7 when at home, you are just wasting money.

It's economy 7, so no, I don't run it 24/7. It does need to be on each night though, or it wont last.

lstar337

martinsurrey wrote: »

I see we cross posted, and it looks like it is the age of the tank, and system...

The more heat it loses, the more I will save by turning it off for the week.

I will turn it off for the holiday, but I think I need to check where my extra units are going.

martinsurrey

lstar337 wrote: »

It's economy 7, so no, I don't run it 24/7. It does need to be on each night though, or it wont last.

you'd be better off turning it off all night, and back on for the last 2 hours of your econ 7 time.

that would give you enough time to heat the tank to max (assuming a 3kw element), while not wasting energy keeping it red hot at 3am.

lstar337

martinsurrey wrote: »

you'd be better off turning it off all night, and back on for the last 2 hours of your econ 7 time.

that would give you enough time to heat the tank to max (assuming a 3kw element), while not wasting energy keeping it red hot at 3am.

You are probably right, but it is controlled by the timer in the meter. I'm not turning it on a 6am each morning or 5am in winter time. I just can't be bothered with that kind of messing.

I could wire in another timer for it, but I would only have to take it all out again when we leave the flat.

[Deleted User]

For a week I would just leave it on. The hot water is there for you on return. Certainly my tired grumpy wife would be even more grumpy with no hot water the moment we got home...

When I was away last Oct for three weeks in..., see flag, I just left the heating on as usual but switched water off. In hindsight I should have just left the water on, grump grump grump...

Though on the next hol with the water being heated by solar...

macman

lstar337 wrote: »

It's economy 7, so no, I don't run it 24/7. It does need to be on each night though, or it wont last.

But it doesn't need to be on for the full seven E7 hours-the last two hours should be more than enough to heat a full tank.

HappyMJ

lstar337 wrote: »

Only 4kWh to heat it from 18c to 58c?

That's scary, why is it taking almost that to keep it ticking over when we use hardly any hot water at all?

Night stores are off, so I may have to investigate where that power is going.

Probably because you are using "some" hot water. It's 4kWh for 90 litres of hot water at at incoming temperature of 18 degrees according to the calc's before so using half that is still 2kWh plus some standing losses. However, my incoming water temperature is much lower at 8 degrees at this time of year. You may also heat the water to a higher temperature...say 65 degrees. Then you have your fridge and possibly a short period of lighting. Have you deducted that from your figures? I'd turn the water off reading the meter before you leave and when you get back and see what the house uses with no hot water and the difference should then be just your hot water usage.

lstar337

HappyMJ wrote: »

I'd turn the water off reading the meter before you leave and when you get back and see what the house uses with no hot water and the difference should then be just your hot water usage.

Yeah, I will do this.