water heating device for heating water, comprising: ∘ a burner or group of burners for generating heat; ∘ a heat exchanger for absorbing heat generated by the burner or group of burners, wherein the heat exchanger is of heat-conducting material and comprises fins configured to guide a fluid in a flow direction from the burner or group of burners arranged close to the heat exchanger at one end thereof to an opposite end where combustion gases leave the heat exchanger, wherein the fins transfer heat between the fluid and the heat exchanger, wherein the heat exchanger further comprises a first conduit for guiding a second fluid, the water heating device further comprising ∘ supply connecting means which are connected to the supply side of the conduit (16, 18) for the fluid cast in the heat exchanger and which can be connected to a supply conduit for water; and ∘ discharge connecting means which are connected to the discharge side of the conduit (16, 18) for the fluid cast in the heat exchanger and which can be connected to a discharge conduit for heated water, characterized in that ∘ the heat exchanger is manufactured from a single piece, ∘ the conduit is recessed into the single piece of heat-conducting material of the heat exchanger, ∘ between the fins are provided transverse fins, integrally formed from the same single piece of heat-conducting material as the heat exchanger, and which transverse fins extend in a direction substantially transversely of the fins over a distance which is less than the distance between the fins and in a direction substantially transversely of the flow direction of the fluid, the transverse fins are arranged alternately close to or on mutually adjacent fins in a configuration to define a meandering path corresponding with the flow direction between the fins, wherein the lateral direction lies substantially perpendicularly of the fins. ∘ a burner or group of burners for generating heat; ∘ a heat exchanger for absorbing heat generated by the burner or group of burners, wherein the heat exchanger is of heat-conducting material and comprises fins configured to guide a fluid in a flow direction from the burner or group of burners arranged close to the heat exchanger at one end thereof to an opposite end where combustion gases leave the heat exchanger, wherein the fins transfer heat between the fluid and the heat exchanger, wherein the heat exchanger further comprises a first conduit for guiding a second fluid, wherein the heat exchanger is of heat-conducting material and comprises fins configured to guide a fluid in a flow direction from the burner or group of burners arranged close to the heat exchanger at one end thereof to an opposite end where combustion gases leave the heat exchanger, wherein the fins transfer heat between the fluid and the heat exchanger, wherein the heat exchanger further comprises a first conduit for guiding a second fluid, ∘ supply connecting means which are connected to the supply side of the conduit (16, 18) for the fluid cast in the heat exchanger and which can be connected to a supply conduit for water; and ∘ discharge connecting means which are connected to the discharge side of the conduit (16, 18) for the fluid cast in the heat exchanger and which can be connected to a discharge conduit for heated water, ∘ the heat exchanger is manufactured from a single piece, ∘ the conduit is recessed into the single piece of heat-conducting material of the heat exchanger, ∘ between the fins are provided transverse fins, integrally formed from the same single piece of heat-conducting material as the heat exchanger, and which transverse fins extend in a direction substantially transversely of the fins over a distance which is less than the distance between the fins and in a direction substantially transversely of the flow direction of the fluid, the transverse fins are arranged alternately close to or on mutually adjacent fins in a configuration to define a meandering path corresponding with the flow direction between the fins, wherein the lateral direction lies substantially perpendicularly of the fins.