It is very dangerous to install a Bosch gas tankless water heater or any other gas appliance in a bathroom or bedroom that draws it's combustion air from that room. Any Bosch gas tankless water heater or gas appliance that is naturally drafting and draws it's combustion air to burn from the room it is installed would deplete the oxygen in the room and cause asphyxiation. The only Bosch gas tankless water heaters that are approved for installation in a bathroom or bedroom would be the direct vent ones. The direct vent units are a twin pipe system and exhaust their gas to the outside and also take their combustion (intake) air from the outside. Any direct vent unit installed in a bedroom or bathroom MUST take the combustion air from the outside.
It is against National Fuel Gas Code (NFGC) section 10.28.1 to install a gas fired appliance in a bathroom or bedroom where the door is normally kept closed. This refers to all gas appliances that take their combustion air directly from the room they are in. The only time a naturally drafting gas appliance shall be installed in a bathroom or bedroom is if they are installed within a closet with a self closing weather-stripped door with no openings. All combustion air shal be obtained from the outdoors in accordance with section 9.3.3 of the NFGC.
Please also consult your local codes and local inspector for a safe installation. Remember it is your life!