Drainwater Heat Recovery A sealed coil that removes the heat from waste hot water for reuse in preheating hot water  Drainwater heat recovery (DHR) devices fit into waste drain lines from hot water uses to recover energy from the drainwater. Energy can be used to preheat cold water going to showers, a water heater, or a dedicated storage device. DHR systems reduce the energy needed for heating water and, in essence, increase the capacity of water heaters.
Heat exchangers for use in DHR vary in terms of pipe sizing, orientation of the drain line (horizontal, vertical, or other), and heat exchanger design. They also vary in cost and the amount of energy savings achieved. There are several residential drainwater heat exchangers commercially available in the U.S. Most have the ability to store recovered energy for later use. Units with storage capacity can recover heat from any waste hot water (e.g., from a dishwasher, clothes washer, bathtub, or shower) which drains through the heat recovery device. Without storage capacity, DHR units provide useful energy recovery only during simultaneous flow of cold supply water and warm drain water (for example, during showering). Some DHR systems are storage-type units that have a tank containing a reservoir of clean water. Drainwater flows through a heat exchanger at the bottom of the storage tank, causing the tank water to warm and rise to the top. The cold water supply to the water heater is preheated by circulation through a coil in the top of the tank. The system is designed so it does not lose a lot of stored energy when cold wastewater runs through the drainwater heat exchanger (because the coldest water is at the bottom of the tank). Another system is a non-storage unit in which a copper heat exchanger replaces a vertical section of a main waste drain. As warm water flows down the waste drain, incoming cold supply water flows through a copper tube spiraled tightly around the copper section of waste drain. Energy is transferred to the cold supply water, which is subsequently directed to the cold side of the fixtures (i.e., shower) or to the water heater. Although the water heater effectively stores some of the useful energy collected by this type of DHR, it is not classified as a storage system. Yet another type of non-storage unit fits horizontally into the main waste drain to exchange energy between the drain pipe and the incoming cold water supply line. The horizontal heat exchange device thermally connects the drain pipe and the cold water supply line. 
 | Drainwater heat recovery units reduce the energy needed to heat water. |
DHR devices are commercially available. Many plumbers are not familiar with DHR installation. However, most systems use common equipment and tools, and installation is relatively simple.
DHR devices typically cost about $100 to $500 or more plus installation. Depending on the type of device used and the plumbing layout, more than one device may be necessary to provide energy recovery for all the hot water uses in the home.
During showering, non-storage DHR devices can reduce hot water costs by up to 60%. However, overall savings will be much less.
DHR units described above are double-walled heat exchangers that meet most local plumbing codes for potable water. Double-walled heat exchangers are covered by the Uniform Plumbing Code, Section 603.3.4; 1995 CABO (Council of American Building Officials) One and Two Family Dwelling Code, Section 3402.3.1; 1998 ICC (International Code Council) One and Two Family Dwelling Code, Section 3402.4.2.1; and 2000 ICC International Residential Code, Section P2902.4.2 - Heat Exchangers.
Not Applicable
Most DHR systems are installed in the main waste drain of the house by an experienced plumber. Depending on the system, it is placed vertically or horizontally in the main waste drain. All DHR units can be used for retrofit or new construction. However, installation will usually be less expensive in new home construction.
Not Applicable
DHR can save energy and increase the capacity of undersized water heaters. Energy savings will vary considerably, depending on location of waste drain pipes, water heaters, bathrooms, and number and lifestyle of occupants. | 
