Instant hot water system

Claim 1

A WATER HEATING AND CIRCULATING SYSTEM FOR A BUILDING HAVING DOUBLE WALLS COMPRISING A HOT WATER HEATER, A HOT WATER SUPPLY LINE CONNECTED TO THE TOP OF SAID HEATER AND INCLUDING A HORIZONTAL RUN SECTION, RISERS IN THE WALLS CONNECTED TO THE HORIZONTAL RUN SECTION AND EXTENDING TO A LEVEL ABOVE THE HEATER, OUTLETS ON SAID RISERS, A RETURN LINE INCLUDING DOWNCOMERS IN THE WALLS EXTENDING TO A LEVEL ABOVE THE HEATER, RETURN BENDS CONNECTING THE UPPER ENDS OF SAID RISERS TO THE UPPER ENDS OF SAID DOWNCOMERS, A HORIZONTAL RUN SECTION TO WHICH THE LOWER ENDS OF SAID DOWNCOMERS ARE CONNECTED, AND A RISER CONNECTING THE LAST MENTIONED HORIZONTAL RUN SECTION ADJACENT THE BOTTOM OF SAID HEATER, A CHECK VALVE IN SAID LAST MENTIONED RISER IMMEDIATELY BEFORE ITS CONNECTION TO SAID HEATER, SAID CHECK VALVE ALLOWING FLOW FROM SAID RETURN LINE INTO SAID HEATER AND PREVENTING FLOW FROM SAID HEATER INTO SAID RETURN LINE, SAID RETURN LINE HAVING A SMALLER CROSS SECTIONAL AREA THAN SAID HOT WATER SUPPLY LINE AND SAID RISERS AND SAID HOT WATER SUPPLY LINE AND A MAJOR PORTION OF SAID RETURN LINE BEING INSULATED AGAINST HEAT DISSIPATION, A MINOR PORTION OF SAID RETURN LINE INCLUDING PART OF SAID LAST MENTIONED HORIZONTAL RUN SECTION AND SAID LAST MENTIONED RISER BEING FREE FROM INSULATION.