The water connections on all Noritz tankless water heaters are 3/4″ with the exception of the NC380, which is 1″. To ensure the maximum performance of your tankless water heater, it is recommended that the water line is sized accordingly with the product installed.
If a 1/2″ copper water line is being supplied to a Noritz tankless water heater, the maximum flow capacity may be limited through the unit.
A local Noritz installer can be located at: https://www.noritz.com/home-owners/find-an-installer/