Abstract: An auxiliary hot water boiler and heat exchange system including a solar heater and adapted for use with a conventional, domestic closed loop hot water heating system and a conventional, domestic hot water heater. A first heat exchanger connected with a solar heat absorber provides a primary source of heat for a supply of water in the boiler. A second heat exchanger provides preheated water for a hot water heater. Water in the boiler is directly fed to a conventional closed loop hot water heating system to provide preheated water therefor. A pair of fireboxes with their flues are arranged one above the other in the boiler and have their flues joined and projected through the top of the boiler. An additional flue is located within the boiler and has an external inlet for connection to an additional boiler. A third heat exchanger provides preheated water to the additional boiler.