Get an electrician (assuming you don’t plan to do it yourself) take the new power supply on the tank prior to time so that you don’t need to live with no hot water a lengthy period of time. Switch off the gas supply to your current water heater then use it until the flame goes out, then (if gas or electric) disconnect it electrically. Close the valves for water (inlet as well as outlet). The tank should be drained. Unplug both the unions that connect the outlet and inlet to the plumbing of the house. With luck, you’ll have planned-in the best way to install matching union halves on the electric water heater. …! Remove your old heater away from the way. The new water heater should be moved towards the front. Connect the two connections (inlet as well as outlet). Doublecheck whether the drain valve has been shut. Install a new overpressure/temperature valve on the water heater, with an overflow pipe directed downwards toward the floor, but stopping well before it touches the floor. Open the water valve for the inlet and then wait for the tank to be pressurized. Release the outlet water valve. Let one person pull “hot” the water out of each tap in order to flush away the air. Close each faucet after the air has stopped flowing out. Connect the new electric supply with the heater. Switch on the appropriate circuit breaker. Determine how to cut or cover the existing exhaust gas vent line. your new heater won’t have any reason to use it. It is best to keep as much of it in in the event that the owner (or or the owner who will follow) decide to ever change over to gas.