The heart of the Drainwater Heat Recovery System is a special heat exchanger made from a standard Drain Waste Vent copper drainpipe surrounded by a coil of copper water tube. As water falls down a vertical section of drainpipe, it clings to the inner surface in a very thin film. The thermal characteristics of this thin film enable very high rates of heat transfer whenever hot water enters the System and cold water is rerouted to simultaneously flow up its coil, as seen in the accompanying illustration at right

The incoming cold water is preheated before going into the water heater and plumbing fixtures thereby saving money and energy while increasing shower-capacity. The S3-60 can bring the cold water temperature up from 10° C to as much as 24° C in the wintertime, while the drain water is cooled by an equal amount; leaving less energy wasted in the sewer.

The Drainwater Heat Recovery System raises the temperature of incoming cold water by recycling free heat from wastewater going down the drain. The more hot water you use, the more energy you save. Actual energy-savings will depend upon the shower flow rate, plumbing system, and diameter and length of pipe installed. Six standard heat exchanger models are available for recycling 40% to 75% of the heat carried down the drain. Preheated water may be fed to the entire house or it can also be fed to just the water heater and/or the cold water input of a shower.