It is generally recommended to have service valves installed when installing a tankless water heater. Service valves, also known as isolation valves or shut-off valves, provide a convenient way to shut off the water supply to the water heater for maintenance, repairs, or replacement without affecting the water supply to the rest of the house. They allow you to isolate the tankless water heater without needing to shut off the water to the entire building. Service valves make future servicing or troubleshooting easier and can help prevent water leakage during maintenance. Therefore, including service valves in the installation of a tankless water heater is a wise choice.