Drain-Water Heat Recovery

    How It Works

       Drain-water heat recovery technology works well with all types of water heaters, especially                 with demand and solar water heaters. Drain-water heat

      exchangers can recover heat from the hot water used in showers, bathtubs, sinks,                  dishwashers, and clothes washers. They generally have the ability to store recovered            heat for later use. You'll need a unit with storage capacity for use with a dishwasher or          clothes washer. Without storage capacity, you'll only have useful energy during the                simultaneous flow of cold water and heated drain water, like showering.

      Some storage-type systems have tanks containing a reservoir of clean water. Drain                water flows through a spiral tube at the bottom of the heat storage tank. This warms            the tank water, which rises to the top. Water heater intake water is preheated by                      circulation through a coil at the top of the tank.

Non-storage systems usually have a copper heat exchanger that replaces a vertical section of a main waste drain. As warm water flows down the waste drain, incoming cold water flows through a spiral copper tube wrapped tightly around the copper section of the waste drain. This preheats the incoming cold water that goes to the water heater or a fixture, such as a shower.

By preheating cold water, drain-water heat recovery systems help increase water heating capacity. This increased capacity really helps if you have an undersized water heater. You can also lower your water heating temperature without affecting the capacity.

Cost and Installation

Purchase prices for drain-water heat recovery systems range from $300 to $500. You'll need a qualified plumbing and heating contractor to install the system. Installation will usually be less expensive in new home construction. Paybacks range from 2.5 to 7 years, depending on how often the system is used, and the temperature of the incoming water, which is dependent on ground temperatures.