System for utilizing heat contained in flue gas

Claim 1

In combination with a heating system comprising a boiler, combustion means for heating water contained in the boiler and a flue for conducting away hot gases resulting from the combustion, the invention comprising a system for recovering heat contained in the flue gas comprising a housing having a flue gas inlet and a flue gas outlet in direct opposition to the flue gas inlet, a first path from the flue gas inlet to the flue gas outlet being defined by the shortest distance between the flue gas inlet and the flue gas outlet, contained in the housing laterally offset from and immediately adjacent said first path a coil having a water inlet and a water outlet, a second, longer path from the flue gas inlet to the flue gas outlet intersecting said coil, laterally offset from and immediately adjacent said coil an unobstructed space in said housing, a third, longest path from the flue gas inlet to the flue gas outlet including said unobstructed space, sole means for directing the flow of flue gas, said flue gas directing means comprising a directing plate pivotally mounted for movement between a first position in which it blocks the first path and a second position in which it blocks the second path, means for sensing the temperature of water heated in the coil by the flue gas, a motor operatively connected to said directing plate for pivoting said directing plate back and forth between said first and second positions and means for actuating the motor in response to the temperature sensed by the sensing means, whereby the directing plate is pivoted into the first position when the temperature of the water in the coil is below a desired level and the flue gas is thereby directed into the second path to further heat the water in the coil, the directing plate is pivoted into the second position when the temperature of the water in the coil is above a desired level and the flue gas is thereby directed into the first path to permit the water in the coil to cool and the third path permits the flue gas to flow from the flue gas inlet to the flue gas outlet in the event that the directing plate is in the first position and the second path becomes obstructed such as by the accumulation of soot in the interstices of the coil.