Peter wrote:
...you'd be looking at around 50kW
more or less depending on the inlet water temp.

Thanks Ed. That's quite some power for sure. I was concerned about
that. So I would be needing a very big gas combi or a three-phase
supply to drive some fancy, semi-industrial, Stiebel-Eltron kind of
electric device.

Peter,

There are stored water combis. They have everything in one box with
some stored water inside. You don't get too concerned about the
innards. The ACV Heatmaster will deliver 38 litres per minute and is
only 35 KW. The domestic meter will deliver around 60 KW. 35KW is just
over half of the meter capacity, so just ticking over. The Powermax,
Gledhill and Viessmann both have high flowrates as well.

The Japanese Rinnai multi points have high flowrates with the downside
of no CH. I am seriously in the market for one of these.