Power-Pipe is a copper drain pipe that is wrapped in smaller copper tubes that coil up the drain pipes exterior. The heat from the drain water warms the copper pipe, the heat then travels to the coils which are full of fresh water on it's way to your hot water heater. By taking the heat from your drain water and transferring some of that to your fresh water you are reducing the amount of energy your hot water heater will have to do to bring your fresh water up to temperature.