I have the smal 117000 btu unit and could possibly but I have 1 shower.
I have run a sink and shower fine. If you need 2 use get the 188000 btu
model by Takagi. Takagi makes Bosches large unit and can come with
remote thermostat. Bosch and takagi heat with flow, the more gpm the
more heat is given. I believe heat starts at 1/2 gpm.