I would think it would depend on what is being done with the hot water ...
If you think about it, a "boiler" implies that heat is being added. This implies the outgoing product is going to be hotter than what comes in. In the end, though, it really depends on what you mean by "hot water" and what is being done with the "hot water."
For example, in a pressurized water nuclear reactor, the water is hot when it comes in (about 275°C (530°F)) and even hotter when it comes out (around 315°C (600°F), all temperatures approximate and not representative of any particular reactor design.)
In a boiling water nuclear reactor, the water is slightly hotter when it goes in (285°C (550°F) same disclaimer, but leaves as steam.
Patricia Lougheed
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