60 degrees?, do you use that hot water alone or mix it with cold? 50 degrees is already hot, for me around 40 degrees is ideal, around body temp.
Anyway, a typical shower heater is around 6000w, maybe miners that pulls at least double like12000w can deliver that heat, it is not efficient(heating-wise) but heat is just a by product, a farm with at least 70-100 cards might do it. Remember the solar solution are just tubes, and it can get as hot as a roof top in a mining room, sometimes it is even hotter than roof tops, also mining rooms deliver near constant heat unlike roof tops.
Size do matter as a storage, that's what water boiler tanks used to do, store hot water before the electric shower heater became the new standard.
Yes, 60 degrees in the tank or at the water heater outlet. Because then the water will run through some more tubes that will cool the water. When you get to the shower, the water should be around 40 degrees.
I am not questioning the power of the miners, capable of heating water, what I am saying is that in order to heat the water effectively, the water had to pass very close to the chips. That's where the heat is. If they pass 20 or 30 centimeters away, they will only catch the air emitted by the miner, who will walk at around 40 degrees. Which will be insufficient to heat water effectively.