Note that when the machine initially started up, it had ~80 W input, a liter per second flow, and the outlet temperature was 40°C. This continued for "a while." I take that to mean long enough for someone to put his hand on the outlet pipe to confirm that the tap water was coming out at body temperature. If I had been there I would do that instinctively, to confirm that the outlet temperature probe is working right.
I would also be scared shitless, not to put too fine a point on it. The machine was obviously outputting ~10 times more power than it was intended to output. In my opinion, there is not the slightest chance this result could be faked by some stage magic technique. Palpable heat at body temperature is instantly recognizable. You would never confuse a tap-water bath for a nice hot 40°C Japanese bath. Even if the flow rate was somehow much lower than it appeared to be, and even if there were magic chambers in the outlet tube that vector the hot water to the outer layer of the tube (as someone suggested), there is no way you could produce a palpable level of heat with this much input power, or with hidden chemical fuel. The 5°C temperature difference later in the test is not palpable. Not easily felt, in any case. That requires you believe the instruments. Measuring this flow rate precisely is not easy, but not necessary either. An error plus or minus 10% would make no substantive difference. - Jed
