EP1150073A2

EP1150073A2 - Heat storing fireplace

Info

Publication number: EP1150073A2
Application number: EP01660025A
Authority: EP
Inventors: Juhani Lehikoinen
Original assignee: Nunnanlahden Uuni Oy
Current assignee: Nunnanlahden Uuni Oy
Priority date: 2000-04-28
Filing date: 2001-02-06
Publication date: 2001-10-31
Anticipated expiration: 2021-02-06
Also published as: FI20001006A0; ATE365299T1; DE60128984T2; FI108162B; EP1150073A3; EP1150073B1; DE60128984D1

Abstract

A heat-storing fireplace, comprising a firebox (1), a smoke flue (2) leading upward from the firebox to convey the flue gases into a chimney flue, and a heat storing mass (3) surrounding the firebox and the smoke flue. Within a certain stretch (4) in the upward leading smoke flue (2) of the fireplace, the inner circumference of the smoke flue increases from the firebox toward the chimney while the cross-sectional area of the smoke flue is either constant or decreasing.

Description

The present invention relates to a heat storing fireplace as defined in the preamble of claim 1.
In a common construction of heat storing fireplaces, the firebox narrows somewhat in its upper part, forming an upward leading smoke flue or secondary combustion space. This space or flue normally extends in a relatively open and unchanged form to the upper part of the fireplace, from where it is either connected directly to the chimney or from where the flue bends to the sides of the fireplace to form downward leading side flues. There are also solutions in which a smoke flue leading upward from the firebox only expands in the upper part of the fireplace, forming a secondary combustion space.
Previously known fireplace constructions are based on the idea that combustion should occur partly in the firebox and partly only above the firebox in a combustion chamber or secondary combustion space. Such a combustion process is disadvantageous especially in the case of inexperienced fireplace users. If the combustion air adjustments have not been properly made, part of the combustion only occurs in the side flues or even in the chimney, and some of the combustible gases may also get into the outer air in an unburned state. Therefore, the efficiency of combustion in the fireplace generally remains relatively low.
In modern times, however, effective solutions have been developed which allow the combustion process to occur substantially entirely in the firebox. In this case, only hot burned flue gases get from the firebox into the chimney. As the entire combustion now takes place in the firebox, it is not necessary to supply any additional combustion air into the flues; instead, in the design of smoke flue structures, efforts can be exclusively concentrated on maximizing the efficiency of heat transfer from the flue gases into the heat storing mass surrounding the flues.
Thus, the object of the invention is to disclose a new type of fireplace smoke flue structure. A specific object of the invention is to disclose a smoke flue structure that allows a maximal efficiency of heat transfer to heat storing mass, thus improving the heat storing properties of the fireplace and its efficiency of heat storage.
As for the features characteristic of the invention, reference is made to the claims.
As the entire combustion process takes place in the firebox, the hottest areas during combustion are at a lower height level than in traditional fireplace constructions. Therefore, the upper part or throat of the fireplace or the first end of the smoke flue is subjected to the most intensive heat stress. To equalize these heat stresses and to guarantee a smooth and effective heat transfer, according to the invention, in a certain substantial stretch of the smoke flue, the inner circumference of the smoke flue leading upward from the firebox of the heat-storing fireplace increases from the firebox toward the chimney while at the same time the cross-sectional area of the smoke flue is either constant or decreasing. Thus, according to the invention, with the rate of flow of the flue gases remaining the same or increasing, the area of heat transfer from the flue gases into the heat storing mass increases as the temperature of the flue gases decreases.
In a preferred case, the cross-sectional area of the flue gas flow decreases continuously from the firebox toward the chimney over the stretch in question. Likewise, preferably over a corresponding stretch of the smoke flue, the amount of heat storing mass surrounding the smoke flue is either uniformly or gradually increasing from the firebox toward the chimney. Thus, in the present invention, as the heat transfer area and the heat storing mass are increasing, an effective and even substantially constant rate of heat storage per unit of length of the smoke flue can be maintained in spite of the falling temperature of the flue gases.
The fireplace of the invention preferably comprises a throat, i.e. a steeply narrowing space above the firebox, after which the smoke flue stretch according to the invention starts. Thus, after the wide firebox, the draft size is generally first reduced by 40-60 %, so the heat conducting surface in the throat is as small as possible and the flow of hot flue gases is fast. In this case, even the thickness of the heat storing mass is at a maximum in relation to the heat transfer area. The said stretch according to the invention equals at least 30%, preferably over 50% and even 70 - 80 % of the length of the smoke flue leading upward above the firebox in the fireplace.
In a preferred embodiment of the invention, the upper part of the smoke flue is provided with one or more partitions consisting of heat storing mass and placed above the stretch according to the invention and possibly also partially within said stretch, said partitions being oriented in a substantially vertical direction and extending in the widthwise direction of the fireplace, i.e. placed side by side in the depthwise direction of the fireplace. These partitions divide the upper part of the smoke flue into at least two and preferably three or more parallel smoke flues. In this way, a larger heat transfer surface which is in contact with hot flue gases can be created in the heat storing mass. The partitions in question preferably divide the entire upper part of the fireplace, i.e. the space under the fire top, into a number of smoke flues laid parallelly in the direction of flow.
In a preferred embodiment of the invention, the partitions in the upper part of the fireplace extend to the edges of the fireplace and downward along the side flues so that they form in the side flues either completely separate collateral flues or flues partially separated from each other. Depending on the height of the fireplace, said partitions may divide the side flues in tall fireplaces e.g. down to about the level of the upper part of the firebox, and in low types of fireplace the partitions may extend even down to the level of the grate. The downward extent of the partitions in the side flues can be defined separately for each fireplace so that the flue gases will not become too cool before flowing out of the fireplace into the chimney.
The invention has been described above mainly with reference to a fireplace construction comprising side flues, in which case the flue gases are passed into the chimney via the lower part of the fireplace. The invention can also be implemented as an embodiment in which the chimney duct is located in the upper part of the fireplace either in the back wall of the fireplace or going upward through the top. In this case, no side flues are needed in the fireplace and the fireplace can be made narrower or the heat storing mass on the sides can be increased. As the upward leading smoke flue need not be provided with a bend into a side flue in the upper part of the fireplace near the fire top, the certain smoke flue stretch according to the invention can easily be made longer with the same fireplace height while at the same time making it more efficient in operation. Thus, it is possible that the smoke flue stretch according to the invention practically extends all the way from the firebox or throat directly to the chimney duct. In this case, the heat transfer area per unit of length of the smoke flue as well as the heat storing mass can be increased at the upper end of the smoke flue by multiple times as compared with the starting end of the smoke flue.
In an embodiment of the invention, the fireplace comprises a dividing partition placed in the upward leading smoke flue, said partition dividing the smoke flue as seen from the front into two adjacent smoke flues, a left-hand smoke flue and right-hand smoke flue. The dividing partition may begin from a point near the firebox, from the level of the throat or a somewhat higher level in the smoke flue, and it preferably extends up to the fire top. Thus, the dividing partition divides the smoke flue into two completely separate parts. As the dividing partition begins from a level just above the firebox, this provides additional heat storing mass in the hottest part of the firebox. Both the left and the right smoke flues are provided with a certain stretch according to the invention, where the heat transfer area per unit of length of the smoke flue increases as the temperature decreases.
In the fireplace of the invention, regardless of whether it is provided with side flues or with a chimney duct in the upper part of the fireplace, it is preferable that, after the inventive certain stretch of the smoke flue, the smoke flue in the upper part of the fireplace expands so that both the cross-sectional area and the heat storing area per unit of length of the smoke flue increase. In this way, after the flue gases have cooled down significantly, their flow rate is reduced, which means that, in spite of a smaller temperature difference, thermal energy from the flue gases can be more effectively stored in the surrounding mass. It is also to be noted that a similar reduction in the rate of flow of the flue gases, although on a smaller scale, already occurs in the inventive smoke flue stretch although the cross-sectional area of the flow remains constant or even if it is somewhat reduced. This is because the volume of the flue gases is reduced as their temperature falls. Thus, throughout the length of the rising smoke flue, as the flue gases are getting cooler, their flow rate is reduced, causing more effective heat transfer, which compensates for the diminution in heat transfer resulting from the smaller temperature difference.
The fireplace construction of the invention has significant advantages as compared with prior art. The heat storing mass is not subjected to an excessive heat load immediately after the combustion; instead, the entire heat storing mass above the firebox is heated as uniformly as possible as the heat flow is substantially equal in the whole area of the heat storing mass. Thus, especially in soapstone fireplaces, the heat conduction properties of the material can be more effectively utilized, with the result that the heat loads and thermal expansions are uniform and no significant displacements or tensions occur in the structures. Due to the effective heat transfer, the efficiency of the fireplace is substantially improved as compared with prior art. In addition, in spite of the larger heat storing capacity of the fireplace of the invention, the external surface of the fireplace does not become too hot and the fireplace causes no excessive heating of the chimney and other structures connected to it, which is of essential importance in regard of fire safety.
In the following, the invention will be described in detail with reference to the attached drawings, wherein
Fig. 1 presents an elevation view of a heat-storing fireplace according to the invention,
Fig. 2 presents a cross-sectional view the fireplace in Fig. 1,
Fig. 3 presents another cross-sectional view the fireplace in Fig. 1,
Fig. 4 presents a third cross-sectional view the fireplace in Fig. 1,
Fig. 5 presents a fourth cross-sectional view the fireplace in Fig. 1,
Fig. 6 presents a fifth cross-sectional view the fireplace in Fig. 1,
Fig. 7 presents a sixth cross-sectional view the fireplace in Fig. 1,
Fig. 8 presents a seventh cross-sectional view the fireplace in Fig. 1,
Fig. 9 presents an eighth cross-sectional view the fireplace in Fig. 1,
Fig. 10 presents a second and a third embodiment of the invention,
Fig. 11 presents a cross-sectional view of the fireplace in Fig. 10,
Fig. 12 presents a fourth embodiment of the invention,
Fig. 13 illustrates the structure of the upper part of the fireplace in Fig. 12, and
Fig. 14 presents a fifth embodiment of the invention.
Fig. 1 illustrates a heat-storing fireplace according to the invention, which is preferably entirely made of soapstone elements except for the grate and other metal parts, which is a technique known in itself. The fireplace comprises a firebox 1 placed above the grate 15 and becoming narrower at the throat 5, forming an upward leading smoke flue 2. The smoke flue 2 as well as the firebox 1 are surrounded at their sides by heat storing masses 3 and, similarly, the fireplace has heat storing masses at the back of the firebox 1 and on the front and back sides of the smoke flue, said masses defining the firebox and smoke flue in a manner known in itself. In the upper part of the fireplace below the fire top 6, the smoke flue 2 bends to both sides, forming downward leading side flues 7. The shell of the fireplace consists of side walls 8, a capping piece 10 above the fire top 6 and insulating material 9, and front and back walls known in themselves, which are not shown in the drawing. The side walls 8 consist of a double stone 16 and a surface stone 17 as is known in prior art.
In the direction of flow of the flue gases, the flues in the fireplace are constructed as follows. The levels at which the cross-sections in Fig. 2 - 8 have been taken are indicated on the left-hand side of Fig. 1. In addition to the smoke flues and the heat storing masses between them, the cross-sectional views also present the masses surrounding them and forming the shell of the fireplace as these play a significant role regarding overall heat flow and heat storage.
In Fig. 2, the firebox 1 is placed centrally between heat storing masses 3. Placed on the other side of the heat storing masses 3 are side flues 7. All these are surrounded by double stone 16, with surface stone 17 covering its outer surface and forming the shell of the fireplace.
In Fig. 3, the firebox narrows in the throat 5 to form a narrower smoke flue 2, i.e. the heat storing masses 3 are thicker in the widthwise direction of the fireplace. At the beginning of the smoke flue 2, its cross-sectional area equals about 15 units and its inner circumference about 16 units. At the same time, after the throat 5 in the vertical direction, the heat storing masses 3 have been made narrower from the side of the side flues 7 so that the cross-sectional area of the side flues has increased by about 50%. The significance of this will be described later on.
In Fig. 4, the certain smoke flue stretch 4 according to the invention begins to be formed. In other words, parts 11 begin to project from the edges of the smoke flue 2 in a smooth and stepless manner toward each other so that the cross-section becomes a toothed pattern which grows upward in the smoke flue. At the same time, the cross-sectional area decreases. In Fig. 4, the cross-sectional area equals about 13 units and the circumference about 20 units. Of course the structure may also be formed in a stepwise manner, in which case e.g. the soapstone elements used may be rectangular parallelopipeds of different sizes.
In Fig. 5, the toothed pattern has become still larger, having a cross-sectional area of about 12 units and a circumference of about 22 units, while the cross-sectional areas of the side flues 7 remain constant.
Further, in Fig. 6 parts 11 approach each other while the surfaces 12 of the masses 3 between them are already somewhat farther removed from each other. Thus, the area is still about 12 units, but the circumference is increasing further, equaling now about 28 units.
In Fig. 7, parts 11 have coalesced and the smoke flue 2 has been divided with partitions 13 into three parts of the equal cross-section. The circumference now equals about 30 units while the area is still about 12 units.
As illustrated in Fig. 8, the width of the smoke flues 2 increases further as the partitions extend upward to the fire top 6. Thus, the partitions 13 divide the space below the fire top 6 into three separate smoke flues 2 placed side by side as seen in the direction of flow. Thus, in Fig. 8, near the top of the heat storing partition masses 3, where they already have a pronounced curvature, the circumference of the smoke flues 2 now equals about 36 units and the area about 15 units.
In Fig. 9, above the heat storing partition masses 3, the partitions 13 form three separate smoke flues 2 placed side by side in the direction of flow of the flue gases, each smoke flue extending through the entire width of the fireplace.
Above the masses 3 surrounding the smoke flues from their sides, these smoke flues turn toward the edges and downward, forming side flues 7. Thus, the side flues 7 on both sides of the firebox are divided by the partitions 13 into three separate side flues down to the level of the throat 5. The lower ends of the partitions 13 are at the level of the throat 5, and from here downward continuous side flues are formed on both sides of the fireplace. The side flues meet in the lower part of the fireplace in a manner known in itself, conveying the flue gases into the chimney.
As can be seen from Fig. 1, the side flues 7 expand inward, i.e. toward the heat storing mass 3, between the section planes presented in Fig. 2 and 3. The expanded side flue extends all the way to the top. As the side flues are expanded in the inward direction, i.e. toward the heat storing mass 3, the heat transfer surface toward the heat storing mass 3 is also increased. Therefore, the heat transfer area toward the interior mass in the side flue is clearly larger than the corresponding area toward the shell, which means that heat is more effectively transferred toward the interior mass, especially because the amount of heat storing mass is greater in the interior parts and the temperature difference is greater during the early part of a heating spell. Due to this construction, the outer surface is not heated too much and the heat emission time is prolonged as the heat is stored inside the fireplace rather than in the surface layer.
The above-described construction according to the invention comprises in the smoke flue from the throat upwards a new type of structural stretch where the circumference of the cross-section increases while the cross-sectional area decreases or remains constant. At the same time, the amount of heat storing mass surrounding the rising smoke flue increases. Thus, with the amount of heat storing mass increasing and the heat absorbing area also increasing, a fast and even substantially constant rate of heat storage per unit of length of the smoke flue can be maintained although the temperature of the flue gases naturally falls at the same time. Therefore, in the inventive construction, the heat energy contained in the flue gases is transferred into the surrounding heat storing mass more effectively and faster than in traditional fireplace constructions.
In the fireplace of the invention, the efficiency and speed of the heat storing process can be varied by varying the number of parallel smoke flues used, both in the rising smoke flue, in the space below the fire top and in the side flues. The heat transfer area can be tripled or quadrupled by simultaneously increasing the amount of heat storing mass. In this way, the heat storing properties of a fireplace type can be varied without changing the external dimensions or form of the fireplace.
Fig. 10 presents in the same fireplace two embodiments of the invention slightly differing from each other, separated from each other with a broken line. The fireplace substantially corresponds to the one in Fig. 1 and it comprises a shell consisting of surface stone 17 and double stone 16 on the sides and a fire top 6, insulating material 9 and a capping piece 10 on the top. Above the grate 16 there is a firebox 1 which narrows upward in a throat 5. In this embodiment, the throat 5 narrows both on the lateral sides and on the front and back sides of the firebox.
At the edges of the firebox 1 there are heat storing masses 3 which extend upward to a level close to the fire top 6. In the depthwise direction of the fireplace, the masses 3 extend from the front part of the shell to its back. Between the masses 3 and the lateral parts of the shell, side flues 7 are formed which convey the flue gases downward toward a chimney duct in the lower part of the fireplace. Disposed in the smoke flue between the masses 3 is a dividing partition 18 extending from the fire top 6 nearly to the level of the throat 5. The dividing partition 18 is made of heat storing mass and extends in the depthwise direction from the front part of the shell to its back. It divides the smoke flue leading upward from the firebox into two separate flues, a right-hand smoke flue 19 and a left-hand smoke flue 20.
The left-hand smoke flue 20 is provided with an inventive structure as presented in Fig. 1, in which a partition 13 growing from the mass 3 increases the heat storing mass and the heat storing area per unit of length of the smoke flue. Depicted in the right-hand smoke flue 19 is another embodiment, in which a partition 13 begins to develop continuously from both sides of the smoke flue, i.e. both from the heat storing mass 3 and from the dividing partition 18. In addition, the dividing partition 18 in this embodiment is of a thickness decreasing toward the top. Likewise, the heat storing mass 3 becomes narrower at its upper end. In this way, a larger heat storing area is formed by the partitions 13 in the smoke flue 19. At the same time, excessive diminution of the cross-sectional area of the flow is prevented, thus ensuring that the flow rates will not become too high.
As compared with the embodiment in Fig. 1, the fireplace with a dividing partition 18 has the advantage that a larger amount of heat storing mass and especially a larger heat storing area can be provided near the throat and the lower part of the smoke flue, where the flue gases are hottest. As shown in the sectional view in Fig. 11, embodiments provided with a dividing partition 18 also comprise parts 11 projecting from the heat storing masses 3 toward the smoke flues, which parts increase both the heat transfer area and the amount of heat storing mass per unit of length of the smoke flue.
Fig. 12 presents a sectional view of an embodiment in which the fireplace has no side flues but instead has a chimney duct disposed in its upper part and going up through the top. The firebox 1 narrows in the throat 5 both on the lateral sides and on the front and back sides. The smoke flue beginning after the throat expands to a width substantially corresponding to the cross-section of the firebox. The edges of the firebox, i.e. the surface stone 17 and the double stone 16 form heat storing masses around the smoke flue. In addition, placed in the upward leading smoke flue there are two dividing partitions 21, i.e. structures of heat storing mass, which divide the smoke flue into edge flues 22 and 23 and a middle flue 24. The dividing partitions 21 extend from a level somewhat above the throat 5 to a level below the fire top but at some distance from it so that the flue gases can flow below them, by their sides and above them.
As in the embodiment in Fig. 1, the smoke flue of this fireplace also comprises a certain inventive stretch in which the heat storing mass and the heat storing area increase as the cross-sectional flow area decreases or remains unchanged.
Presented in the edge flues 22 and 23 are two embodiments of the partitions 13 which differ somewhat from each other. In the left-hand smoke flue 22, partitions 13 like those in the embodiment in Fig. 1 begin to develop in a stepwise manner, starting from the mass 21. The width of the partitions increases toward the top, thus reducing the cross-sectional area of flow and increasing the amount of heat storing mass as well as the heat transfer area of the mass per unit of length of the smoke flue.
In a corresponding manner, in the right-hand smoke flue 23, partitions 13 develop continuously from the mass 21 as in the embodiment in Fig. 1. In addition, in the middle flue 24 between the dividing partitions 21, partitions 13 begin to develop from both masses 21 toward each other. Finally, the partitions 13 are continuous and divide the space below the fire top 6 into separate smoke flues placed side by side.
The stepwise structure of smoke flue 22 permits a simpler and cheaper implementation because all the soapstone bricks to be used may be of a rectangular shape and no beveled surfaces are needed. Further advantages associated with the stepwise structure are a larger heat transfer area and a turbulence of the flue gases caused by the stepped surface, both of these features being conducive to more effective heat storage in the surrounding masses.
Fig. 13 visualizes the upper part of the fireplace in Fig. 12, showing how the smoke flues coalesce under the fire top 6. On both lateral sides of the fireplace there are three separate rising smoke flues 22. Between the heat storing masses 21 there are likewise three separate rising smoke flues. After the masses 21, the rising smoke flues 22 at the edges bend under the fire top toward the middle. In the middle region of the fireplace, the partitions 13 are provided with cut-outs 25 permitting communication between the spaces between the partitions. A chimney duct 26 going through the fire top 6 conveys the flue gases from above the cut-outs 25 into the chimney.
Fig. 14 presents a fireplace which partially corresponds to the fireplace in Fig. 1. It comprises a shell consisting of a surface stone 17 and a double stone 16 and, on the top side, a fire top 6, insulating material 9 and a capping piece 10. Disposed above the grate 15 is a firebox 1 which narrows upward in a throat 5. In this embodiment, the throat 5 narrows on the lateral sides as well as on the front and back sides of the firebox.
Placed on the sides of the firebox 1 are heat storing masses 30 extending upward only to the height of the throat. In the depthwise direction of the fireplace, these masses 30 extend from the front part of the shell to its back. Above the masses, metal walls 31 resting on the masses 30 extend from the level of the throat perpendicularly upward to a level near the fire top 6. The metal walls 31 have rounded upper ends 32.
Between the masses 30 and metal walls 31 and the lateral sides of the shell, side flues 7 are formed which lead the flue gases downward toward a chimney duct in the lower part of the fireplace. Disposed in the smoke flue between the metal walls 31 is a dividing partition 33 extending from the fire top 6 downward nearly to the level of the throat 5. The dividing partition 33 is made of heat storing mass and extends in the depthwise direction from the front part of the shell to its back, dividing the smoke flue leading upward from the firebox into two separate flues.
As in Fig. 1, the structure comprises partitions 13 consisting of heat storing mass which begin gradually from the lower part of the dividing partition 33, growing toward the rounded portions 32. From here upward, the partitions 13 divide the smoke flues bending to both sides e.g. into three separate smoke flues placed side by side, which continue as separate flues leading into the side flues 7 down to the level of the throat 5.
One of the functions of the metal walls 31 in certain embodiments is to increase the heat transfer area of the heat storing masses 13 and to cause heat to be stored in the central masses 13 and 33 of the fireplace rather than in a heat storing mass 3 located closer to the outer surface, and partially to increase the degree of heat storage in the masses of the side flues. In this way, more heat can be stored in the central structures of the fireplace, i.e. in the massive dividing partition 33 between the metal walls 31 and in the partitions 13, which become hot during heating of the fireplace, the heat emission time being thus prolonged.
In the foregoing, the invention has been described by way of example with reference to the attached drawings while different embodiments of the invention are possible in the scope of the inventive idea defined in the claims.

Claims

Heat-storing fireplace, comprising a firebox (1), a smoke flue (2) leading upward from the firebox to pass the flue gases into a chimney flue, and a heat storing mass (3) surrounding the firebox and the smoke flue, characterized in that, within a certain stretch (4) in the upward leading smoke flue (2), the inner circumference of the smoke flue increases from the firebox toward the chimney flue while the cross-sectional area of the smoke flue is either constant or decreasing.
Heat-storing fireplace as defined in claim 1, characterized in that, within the said stretch (4), the cross-sectional area of the smoke flue (2) decreases continuously from the firebox toward the chimney flue.
Heat-storing fireplace as defined in claim 1, characterized in that, within the said stretch (4), the amount of heat storing mass (3) surrounding the smoke flue (2) increases from the firebox toward the chimney flue.
Heat-storing fireplace as defined in any one of claims 1 - 3, characterized in that it comprises a throat (5), i.e. a steeply narrowing portion above the firebox (1) before the said stretch (4) in the smoke flue (2).
Heat-storing fireplace as defined in any one of claims 1 - 4, characterized in that the smoke flue is provided with partitions (13) placed above the said stretch (4) and consisting of heat storing mass, said partitions dividing the upper part of the smoke flue into at least two, preferably three or more smoke flues placed side by side in the direction of flow and in the depthwise direction of the fireplace.
Heat-storing fireplace as defined in claim 5, characterized in that the partitions (3) begin gradually, continuously or stepwise in the said stretch (4).
Heat-storing fireplace as defined in claim 5, characterized in that the partitions (13) divide the space below the fire top (6) into parallel smoke flues in the direction of flow.
Heat-storing fireplace as defined in claim 5, characterized in that the partitions (13) extend in the fireplace in smoke flues bending downward to the sides into side flues (7), forming parallel side flues.
Heat-storing fireplace as defined in claim 8, characterized in that the partitions forming the parallel side flues extend substantially to the level of the upper part of the firebox.
Heat-storing fireplace as defined in claim 8, characterized in that the partitions forming the parallel side flues extend substantially to the level of the grate.
Heat-storing fireplace as defined in claim 8, characterized in that the parallel side flues (7) have at their upper end a larger width toward the heat storing mass than at their lower end, forming a larger heat transfer area inside the fireplace than outward.
Heat-storing fireplace as defined in claim 11, characterized in that the side flues (7) are wider in the region above the throat (5), where the amount of heat storing mass (3) is substantially larger than at the level of the firebox (1).
Heat-storing fireplace as defined in any one of claims 1 - 7, characterized in that the parallel smoke flues (2) merge into a chimney duct near the fire top in the upper part of the fireplace.
Heat-storing fireplace as defined in any one of claims 1 - 13, characterized in that the upward leading smoke flue (2) is provided with a dividing partition (18) that divides the smoke flue into two separate upward leading smoke flues (19,20).
Heat-storing fireplace as defined in claim 14, characterized in that the dividing partition (18) begins from above the firebox (1), e.g. substantially from the level of the throat (5).
Heat-storing fireplace as defined in claim 14, characterized in that the dividing partition (18) extends to the fire top (6).
Heat-storing fireplace as defined in any one of claims 1 - 16, characterized in that it comprises a metal wall (31) placed around the heat storing central masses (33,13) and at least partially forming the smoke flues to allow greater heat storage in the heat storing central masses and in the masses in the smoke flues.
Heat-storing fireplace as defined in any one of claims 1 - 17, characterized in that, above the said stretch (4) in the upward leading smoke flue (2), both the inner circumference and cross-sectional area of the smoke flue increase, so that, as the flue gas flow rate is substantially reduced, there is more time for heat to be stored in the surrounding mass and effective heat storage occurs in spite of a smaller temperature difference.