The hot water in your home is literally poured down the drain. The ThermoDrain is designed to recover this wasted energy and transfer it directly back into your potable water heating system thereby significantly reducing the costs associated with hot water heating. The ThermoDrain's simple design consists of a single 3/4" copper potable water tube wound around a central copper drain tube. The ThermoDrain replaces a section of your vertical drain stack. (Lengths vary from 12" to 100", 42" is the most common length). Wastewater (from your shower or other source of wasted heated water) flowing down the drain transfers heat to the inner drain tube of the ThermoDrain. At the same time, cold water is flowing in the outer coil trying to cool down the warm drain pipe. A heat exchange takes place. The cold water in the coil extracts the heat energy from the drain pipe.