Question about hot water tank

[sheepdogdelight]

This is probably a stupid question, but I can't get my head around it ..

Our hot water is currently timed to heat up for an hour a day. We have a standard gas central heating boiler.

If we use hot water during this time, my expectation is that the hot water is used from the tank; the tank then fills up with cold water which is heated up to hot so we still have a full tank of hot water.

if we use hot water not during this time, what happens? Does the tank still fill with cold water, which means the overall temperature in the tank will decrease as it's now a mixture of hot and cold
Or, does the tank just stay partially full in which case the water stays hot (hopefully, assuming the tank is well enough insulated) and we can keep using properly hot water until it runs out?

Also, is it better (no Economy 7 or anything) to heat the hot water at a time when you are not using it, or a time when you are using it? Or does it make no difference?

I think the pipe leads from the top of the tank, where the water is hotter, so even if it fills with cold, you still have got water. I’m not 100% sure if it does still fill when it’s off. It must do though, the water goes cold when you run a tap rather than there being no water.

Still got HOT water

Hot water comes out of the tank at the top, cold water goes in at the bottom. Because heat rises, the cold water coming in at the bottom doesn't mix up with the hot at the top too much, so doesn't make much of a difference.

The temperature of the hot water will go down slowly as you use it and cold water replaces the hot in the tank - but as other people said it doesn't mix so well, so the water remains pretty hot.

If the water heating is switched on while you are using the hot water then at some point the boiler will come back on automatically to heat it back up. Which is great if you need more hot water than the tank can hold, and not so great if you don't.

The reason is, you don't want to be left with a tank full of hot water that you don't use after you have used what you need because that is wasteful.

So the best thing to do is turn on the water heating before you need the water to get a tank full of hot water. Then turn off the heating, then use the water. And at the end after you use the water the tank will be cold(er) and you wait until you need hot water again to heat it up.

You can only use the above strategy if 1 tank will hold enough for you to use. So for example my tank will get me 2 showers and 1 washing up before the water becomes too cold to use. This is enough for what I need in the morning.

Thanks so much for the explanations - that makes perfect sense now!