Boiler for domestic central heating - has return water passed through insulated tube bundle against gases flow to extract additional heat

摘要

The boiler consists of two horizontal tube bundles. One is situated over the combustion chamber (5), the gases passing from the burner (2) into a header (6) and then into this tube bundle. The gases leave this bundle and pass into another heater (10). The second bundle (13) is above the first and is insulated (12) from the surrounding heated water. The gases flow from front to rear headers and into the chimney (19). The return water from the heating system enters (18) the area round this bundle and is preheated by passing from rear to front, before again leaving (17) the boiler.