An exchanger for heating boilers is formed of an external prismatic framework, a burner and an exhaust duct, characterized in that it includes a block of tubes formed of a plurality of tube sections positioned against one another horizontally and vertically, separated at equal distances from one another and integrated in a prismatic housing creating between them a closed circuit of water, leaving the tube sections free, forming different levels separated by deflectors in order to control the inflow and outflow of the gases produced by combustion, directing the gases as desired through the different levels, capturing the heat along the path of the gases in order to quickly heat the water in the circuit without losing calories and reducing fuel consumption as much as possible.