Installing an On-Demand Water Heater

Run Power for the Unit

It will be either a 120- or 240-volt circuit, and it must be a circuit wholly devoted to the heater. Either voltage requires 8-gauge wire, and the section exposed to the area under the sink must be armored cable. If the manufacturer's instructions call for a larger cable, the National Electrical Code says you must comply.

If You're Installing the Heater Under an Existing Sink

Turn off the water line. Drain the line by opening a faucet at a lower point somewhere in the house. Solder a cutoff valve onto the pipe stub that comes from the floor or wall. Solder a second valve onto what's left of the line that runs to the faucet, cutting the line as necessary to allow room for the heater.

Screw the Unit to the Wall

Follow the manufacturer's directions. Connect the water supply line to the cold in-feed fitting with soldered copper pipe or high-pressure flex connections as shown here. Wrap Teflon tape around the threads before you make the connection and hand-tighten. Finish tightening with a wrench. Connect the line going to the faucet to the hot water outlet using the same materials.