A tankless water heater will require a dedicated circuit as specified by the installation manual of the unit that has been selected.
Tankless water heater wires installation.
If you need additional space in the panel for the circuit breaker then a quad circuit breaker may be allowed as specified by the make and model of the panel.
Use bell hangers to hold pipe securely in place against the wall.
I bought an ecosmart 18 tankless water heater.
What size wiring is recommended when installing a tankless hot water heater.
Clean the pipes and connectors before soldering to remove.
This video is an instructional video that gives you insight how to install tankless.
Community answer you will probably need 220 volt service as with an electric dryer with at least 60 amps.
This will also make it easy to apply pipe insulation.
Tie in new hot and cold water lines to the existing water lines with copper pipe and run the lines to the new water.
Wire connections for a ecosmart 18 tankless water heater.
Wires to the tankless water heater reviewing the electrical question.