US PATENT SUBCLASS 165 / 221
.~.~.~.~.~.~ Additional return main (e.g., four pipe system, etc.)

Current as of: June, 1999
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165 /   HD   HEAT EXCHANGE

200  DF  WITH TIMER, PROGRAMMER, TIME DELAY, OR CONDITION RESPONSIVE CONTROL {14}
201  DF  .~ Having heating and cooling capability {13}
205  DF  .~.~ Plural temperature regulators for plural zones {8}
218  DF  .~.~.~ Central temperature conditioned liquid supplied to each zone {1}
219  DF  .~.~.~.~ Separate supply and return mains (e.g., two pipe system, etc.) {1}
220  DF  .~.~.~.~.~ Additional supply main (e.g., three pipe system, etc.) {1}
221.~.~.~.~.~.~ Additional return main (e.g., four pipe system, etc.)

DEFINITION

Classification: 165/221

Additional return main (e.g., four pipe system, etc.):

(under subclass 220) Subject matter further including a second distinct return conduit extending from the heat exchanger to the common liquid supply source.