Boiler

Abstract

A boiler comprising an enclosure which forms a heating chamber which contains water to be heated and accommodates a firebox which forms a combustion chamber with a burner associated therewith which comprises a combustion head, arranged in the combustion chamber and connected to a supply duct, and provided with a premixer of combustion air and combustible gas which is interposed along the supply duct. The combustion chamber is connected to a stack for the evacuation of the combustion gases into the external environment, elements being further provided for generating a flow of a mixture of air and gas toward the combustion head; at least one duct being provided for conveying the combustion gases which connects the stack to the supply duct.

What is claimed is: 
     
         1 . A boiler comprising an enclosure which forms a heating chamber which contains water to be heated and accommodates a firebox which forms a combustion chamber with a burner associated therewith which comprises a combustion head, arranged in the combustion chamber and connected to a supply duct, and provided with a premixer of combustion air and combustible gas which is interposed along said supply duct, said combustion chamber being connected to a stack for the evacuation of said combustion gases into the external environment, means being provided for generating a flow of a mixture of air and gas toward said combustion head, and further comprising at least one duct for conveying said combustion gases which connects said stack to said supply duct, said flow generation means comprising means which are adapted to place said combustion chamber in partial vacuum with respect to atmospheric pressure. 
     
     
         2 . The boiler according to  claim 1 , wherein said combustion chamber is connected to a plurality of tubes for conveying the combustion gases, which are arranged in a heat exchange relationship with said heating chamber and lead into a combustion gas collection chamber which is connected to said stack, said means adapted to place said combustion chamber in partial vacuum comprising a fan arranged in said combustion gas collection chamber. 
     
     
         3 . The boiler according to  claim 1 , wherein said at least one duct is connected to said supply duct downstream of said premixer. 
     
     
         4 . The boiler according to  claim 1 , wherein said supply duct is connected in input to the external environment, said premixer comprising a tubular element which is arranged coaxially to said supply duct in order to create a cross-section reduction in said supply duct, said tubular element being connected internally to a gas supply duct and being provided with a plurality of openings for the outflow of the gas into said supply duct. 
     
     
         5 . The boiler according to  claim 2 , wherein said fan is controlled by a variable-speed electric motor.