State of the art During last years the emphasis is done on life environment and reducing of emissions. It is done by combustion of good-class fuels, e. g. wood, coke and gas. However, at their thriftless combustion increases their consumption. In addition, gas is relatively expensive fuel and is replaced in many cases by less valuable fuels, whose combustion subsequently causes a pollution of atmosphere. Generally, the magnitude of chimney effect grows directly proportional with the chimney height and the temperature of combustion gas and is also depends on weather conditions. Under aggravated conditions, for example at big wind or storm, the flue gas can infiltrate back to the heating room. To avoid this phenomenon, there are used among others cowl shaped pipes enhancing a natural chimney effect. The cowl has at the top an attachment cover, e. g. in the shape of hood or revolving head, which-in addition to prevention of infiltration of rainy water-rolls in accordance to running air in order to proceed of venting. Thus, it partially increases a chimney effect. A disadvantage of all these cowl designs is a higher draught of chimney with relatively low effects on production of emissions and saving of fuel.

The task, which is being done, was to propose a new type of cowl, which is fully functioning under bad weather conditions. At the same time it should reduce of draught onto the optimal values to ensure a perfect combustion with subsequent saving of fuel and prevention of sedimentation of carbon particles on inner wall of venting unit-of course, if the venting unit meets valid standard specifications.

The matter of invention 1. The cowl for a reduction of chimney draught is formed by a body with orifice to the venting unit, which upper part is concentric and in distance to the lower part-both these part are mutually linked by fitting stack with the diameter dl X and at least one input hole, whereas lower part is attached to the body and has the diameter d22 and at least one output hole.

2. The lower part has openings for a conscription of condensates. It helps to increase a conscription of combustion gas from the chimney and prevents in that way its blowing-in to the venting unit. It has also a connecting conical part equipped by a system of apertures (they may have various geometric shapes) and a regulatory part (for optional settings). The part ends by a hood, which is equipped in bottoms by a baffle block, which improves a fluxion of combustion gas and improves the function of the cowl. Inside the cowl there is placed a diffuser.

According to the invention the cowl essentially reduces a draw-off mechanism of combustion of gas going out of the chimney simultaneously improves a gas burning of all fuel types in kettles, thereby increases their effectiveness. It can be reached by mutual ratios of diameters dl, d2 and height h of the cowl in dependencies on the draught, diameter and height of venting unit. It has to be fulfilled the condition dl < d2, whereas both diameters depend upon the height h of venting unit and venting diameter dp, volume quantity of combustion gas and its rate fluxion and subsequent speeding of fluxion and synchronous leech onto atmospheric air.

The adapter extends a burning of fuel and its savings and decreases polluting matters out to the atmosphere. For regular function of the cowl it is important that input openings were done in the form of circle, tetragonal, triangle or polygon.

To fix the cowl it is equipped by ribbing. Thus, the cowl is tightened and prevent against undesirable false suction, which can lower its effect. Above the rib there is a hinge and overseal, which enable opening and cleaning of the cowl. For air circulation connecting part and body have the shape of a pipe or tetrahedron or ellipse.

For increasing the dynamics of venting inside the body there is a diffuser to adjust draught, temperature and pressure on recommended values.

Cowl forms in the chimney so-called secondary combustion chamber, which causes a chemical reaction of combustion gas under increasing temperature, pressure and resistance. Thus, the result is saving of fuel and primarily decreasing of discharges of polluting matter spreading out to the atmosphere.

List of figures on drawings Technical solution is clarified on drawings, where figure 1 represents an arrangement of the cowl, figure 2 represents an arrangement of the cowl equipped by a diffuser and figure 3 represents the arrangement of the cowl with connecting part in interior body. Figure 4 combines findings from previous models and further improves technical solving of these models and increases efficiency of their function.

Examples of implementation the invention First variant of cowl arrangement is illustrated on figure 1 and consists from upper part l, equipment with baffle cone of combustion gas 10, organized concentric and in distance above lower part 2. Both these part 1 and 2 are mutually connected by a stack 3 with a diameter d. In top part of the stack 3 mainly in the place below upper part 1 there is set up the system of output holes 6, which are designed for passing of the combustion gas. Lower part 2 is further fasted to the body 4 with a diameter d2 which is over the periphery equipped by the system of input openings 7 designed for air suction. The body 4 is in its bottoms equipped by ribbing 5 for to fix openings of the venting unit.

Second variant of cowl arrangement is illustrated on figure 2. The total arrangement is the same as above-in addition, it is equipped with chimney diffuser 8 and openings to lead away water condensates (holes 9). By using the part 8 it is improved the fluxion of combustion gas and increases in that way the total performance of the whole system.

Third variant arrangement of the cowl is described on the figure 3. Based on figure ! and figure 2, it is completed by the extension stack 3, which ends are equipped by the system of openings (venting apertures 11) next to a diffuser. At this model there was achieved the highest system efficiency.

Fourth variant of the chimney cowl arrangement is described on the figure 4 is based on previous model shown on figure 3-this model is improved in functioning and better efficiency.

This modification is completed by a baffling of combustion gas.

The function of these cowls on chimney vent is as follows: Combustion products running inside the cowl and proceed from the kettle or stove inner through space of the chimney body 4.

By means of input openings 7 created in the body 4 there is absorbed the atmospheric air, which run-around of the lower part 2. The air runs along with combustion gases up and expeditiously flow in direction towards exit ports 6 and stack 3 by which the combustion products are blow out and equally dissipated into the atmosphere. By linear fluxion of combustion gas and leeching of air there sustains constant chimney effect, thereby there is guaranteed better and slower combustion in the kettle or the stove, whereby it increases the cowl's efficiency.

Industrial utilisation The cowl described is possible to utilise for all common venting units, for households and industrial sector. Thus, the invention offers and ideal solution, which significantly decreases emissions and the fuel consumption.

List of marks 1. upper part 2. lower part 3. chimney stack 4. body 5. rib 6. output apertures 7. input apertures 8. diffuser with a stack 9. condensing holes 10. baffle cone of combustion gas 11. venting holes 12. hinge 13. conical part 14. regulatory part 15. hood with hem 16. overseal