This is not for miner cooling. It’s just to have hot water even if the tank heater has been off, or ran out of hot water.
In my region, people have small water heater tanks with a wall switch to turn it off to save energy.
Problem is, when forgetting to turn it on hours before use, there’s no hot water when needed.
So, i guess the obvious answer then is to have inline heater downstream of the heater tank.