Second here, don’t even let a specialist install it, get someone
who is really really competent.

I hired the bosch reccomended dealer and he caused my roof to
fall in.

The venting needs to be double walled and drained,
btw i hear good things about the rennai.

i have a bosch, it’s getting better but it’s real complicated

and for why you need a permit to replace a water heater, sounds
like code changed and the new units may need some serious
reengineering