My house is powered only by electricity, we don’t have gas, so our hot water comes from an immersion heater. As I understand it, this is essentially a big insulated tank with a heating element at the bottom (?).
Because we have “Economy 7” electricity, which means it is cheaper to use power at night (when there is less demand), we have the heater on a timer so it heats the water up overnight. Unless we’re doing a lot of washing or running a lot of baths, there’s usually enough hot water to last the whole day without turning it on at the more expensive daytime rate.
But this is the bit I don’t understand - when using hot water during the day, the temperature seems to stay pretty much constantly hot until right before the hot water runs out. I would have thought that, as the tank refills with cold water to replace what is used, it would cool the entire contents of the tank. But it doesn’t seem to.
So, do immersion heaters only refill once all the hot water is used? If that were the case, then say I’d used 75% of the tank full, but then decided I’d need more hot water and turned the switch on for an hour, it would only be heating the remaining 25% of a tankful. But that doesn’t seem to be the case either - I still end up with a full tank of hot water.
I know this isn’t an important question in the scheme of things, but it bugs me. Please explain the mysteries of the hot water tank!
