> The 28kW limit is from the Boilermakers Union, not ours [IBEW] =P

Ahh gotcha, they must’ve pushed for some good ol trade protectionism after electric boilers came out and high-power tankless water heaters are within their wheelhouse or something like that. I wouldn’t consider it a pressure vessel but I don’t blame them for scooping up the work, lol. I’m not in the union myself, but I do manage IBEW electricians and know enough to be dangerous ;)

> As much as I hate AFCI breakers, I do love a well-designed "stupid" heat-response timeout that's in compliance with the NEC. You're correct that residential waterheaters are not "continuous loads" – had slipped my mind.

I believe electric tank style water heaters under a certain size are considered continuous loads, but tankless are not.

> I used a tankless/instahot heater (and helped install a few hundred in the early 2010s) and am so much happier with my hybrid/heatpump tank-type (it is so much cheaper to operate, requiring a relatively minimal upkeep of: an annual drainage). Plus: there are no "miminum flow" requirements/bullshit, which results in some tempermental dishwashing among the water-conscientious (sp?).

Heat pump water heaters seem amazing, 25% of the power usage of a resistive heater, and especially for $250!

I wasn’t aware of minimum flow requirements for tankless heaters, I suppose it’s necessary to prevent overheating/steam or something? I mostly see tankless water heaters as part of emergency eyewash station installations, most commercial buildings around here either use boiler water for domestic hot water heating or have point-of-use tank water heaters near sinks/bathrooms.