Auxiliary heating system

In combination with a forced-air heating system including a furnace having a heat source therein, a hot air duct connected to said furnace for conveying hot air to a space to be heated, and a cold air duct connected to said furnace for returning cool air from said space to said furnace, the invention comprising an auxiliary boiler adapted to be stoked with combustible material, comprising,

• a boiler tank adapted to be substantially filled with a heat exchanger fluid,
• a firebox extended into said tank and adapted to receive combustible material for heating the fluid in said tank,
• a heat exchanger disposed within said cold air duct,
• a hot water supply conduit connected at one end to said tank and connected at its opposite end to said heat exchanger for supplying warm fluid thereto,
• a cold fluid return conduit having opposite ends connected to said heat exchanger and tank respectively, and
• pump means for pumping hot fluid from said tank through said supply conduit to said heat exchanger whereby cool air moving through said cold air duct is pre-heated as it passes through said heat exchanger,
• a plurality of heating tubes extended through said firebox and in communication with said tank at the opposite ends thereof for heating fluid in said tubes,
• the opposite ends of said heating tubes being disposed in vertically spaced-apart relation whereby fluid heated in said tubes is passed therethrough by convection flow,
• said heating tubes being disposed in a lower portion of said firebox for supporting said combustible material thereon,
• a flue extending upwardly from said firebox through said tank,
• a plurality of heating tubes extending through said flue and in communication with said tank at the opposite ends thereof for heating fluid in said tubes,
• said boiler tank including a top wall, bottom wall, front and rear wall portions, and opposite side wall portions, said firebox including an open end which opens through said front wall portion, and further comprising a movable door adapted to at least partially close said open end at times,
• means for supporting said firebox in spaced relation from said bottom wall, top wall, side wall portions, and rear wall portion whereby said firebox is substantially surrounded by fluid except at the open end thereof,
• a first thermostat operatively positioned in said space to be heated and electrically connected to said furnace for activating said heat source of the furnace when the temperature in said space falls below a first selected temperature, and a second thermostat operatively positioned in said space and electrically connected to said pump means for activating said pump means when the temperature in said space falls below a second selected temperature higher than said first selected temperature whereby said heat source of the furnace will remain inactive for so long as the temperature in said space is maintained above said first selected temperature by said heat exchanger.