The subject of the invention is a water heater for central heating, fired by solid, gas or oil fuel and intended for heat supply to small and medium-sized systems, for which DE-A-410532 forms the closest prior art.

The invention is defined by the claims.

The application of the upper starting flue shortens the route of flue gas and smoke during the heater fire-up phase to minimum and prevents the smoke from getting outside.

In turn, once the throttle of the upper starting flue is closed, the route of the flue gas now surrounding the internal water jacket of the heater and flowing to lower flue, located opposite to the ash box, is extended to maximum while its heat is almost completely transferred to this water jacket thus making the water heater highly efficient. This application of very extended route of the flue gas which surrounds a maximally large surface of the inner water jacket causes that, in case of heater firing with solid fuel, especially the sawdust , its combustion time become extended with the resulting reduction in sawdust consumption by about 50%.

The invention is presented in its execution example in the drawing wherein Fig. 1 illustrates the heater in a perspective view, Fig. 2 shows the same heater in vertical section along the A-A line, and Fig. 3 shows the same heater in vertical section along the B-B.

The water heater in form of rectangular prism with a slanted upper part of the front wall has the upper starting flue 1 provided with the throttle 2 installed in the upper wall 3 of the outer steel jacket 4 and the lower flue 5 located at the bottom of the rear wall 6 of this jacket opposite the ash box 7. In the combustion chamber 8 there is the inner water jacket 9, separated from the outer steel jacket 4 with flue-gas passes 10, whereas the front wall 11 of the steel jacket 4 above the loading hole 12 is provided with water jacket 13 connected with the water jacket 9, whereas the side wall 14 of the heater is provided with a stub pipe 15 for installing the fuel-gas or oil burner, not shown on the drawing.

The inner water jacket 9 consists of two water jackets 16 and 17 connected by the rear water jacket 18 and top water jacket 19, whereas in the lower loading chamber 20 the water jackets 16, 17 and 18 are bent inward, so that they surround the fire grate 21 whereas flue-gas flow passes 10 are provided with cleaning devices 22 serving for soot removal from heater walls which form those passes.

On both sides of the ash box 7, provided with door 23, there are blanking covers 24 which enable cleaning of those side walls which adjoin the ash box 7. During the heater fire-up, especially with wood, sawdust or other solid fuel, the throttle 2 of the starting flue 1 is opened to enable the escape of smoke and flue gas by the shortest route to the chimney to which the flue connected. The flow of flue gas during fire-up phase is marked in Figs. 2 and 3 with broken arrows.

On the other hand, once the heater fire-up phase is over, the throttle 2 of the flue 1 is closed tightly while turning it by 90° and, as a result, the flue gas flows through passes 10 to the lower flue 5 also connected to the chimney. The route of these flue gases is marked with continuous line arrows.