Claims
- 1. A wood burning furnace comprising:
- a furnace housing having front and rear walls, opposite side walls, and top and bottom walls,
- a firebox within said furnace housing having a front wall joined to said front wall of said housing, the remainder of said firebox being spaced inwardly from at least some of said rear, side, top and bottom walls of said housing to define a boiler chamber therebetween,
- said top wall of said housing having an inlet opening in communication with said boiler chamber; said rear wall of said housing having an inlet opening in communication with said boiler chamber;
- a flue extending through said housing and said boiler chamber and extending approximately half way into said firebox and being in spaced relation below said top wall of said firebox;
- said front walls of said firebox and said housing being provided with a door opening having an upper edge and a lower edge and providing communication from the exterior of said firebox to the interior of said firebox;
- a door having upper and lower edges and being positioned in covering relation over said door opening;
- a main draft opening in said firebox adjacent the bottom thereof and below said door opening, said main draft opening providing communication of air from the exterior of said housing to the interior of said firebox;
- a secondary draft opening in said firebox above said main draft opening and providing communication of air from the exterior of said housing to the interior of said firebox, said secondary draft opening comprising at least one hole in said door adjacent said upper edge of said door;
- smoke damper means positioned between said secondary draft opening and the interior of said firebox to prevent smoke from exiting said secondary draft opening, said damper means having an upper edge and a lower edge, said upper edge of said damper means being hinged about a horizontal axis adjacent said upper edge of said door opening whereby said damper means may be pivoted inwardly about said horizontal axis during insertion of wood into said firebox through said door opening;
- said lower edge of said damper means being spaced downwardly from said flue and said secondary draft opening and upwardly above said main draft opening whereby fresh air will pass from said secondary draft opening downwardly below said lower edge of said damper means and will mix with and be heated by hot gases which are rising within said firebox before said hot gases reach said flue.
- 2. A furnace according to claim 1 wherein said firebox is spaced inwardly from all of said top, bottom, rear, and side walls of said housing wherein said boiler chamber extends above, to the rear and to each opposite side of said firebox.
- 3. A furnace according to claim 2 wherein a pump is connected to said intake opening for circulating water through said boiler chamber and outwardly through said outlet opening an aquastat positioned within said boiler chamber, and means connecting said aquastat to said pump for controlling the actuation and deactuation of said pump in response to temperature changes within said boiler chamber.
- 4. A furnace according to claim 1 wherein a draft control means is mounted on said housing and comprises a power means, a chain connected to said power means, and a main draft door over said main draft opening, temperature sensing means within said boiler chamber, and responsive to temperature changes within said boiler chamber to acturate and deacturate said power means whereby actuation of said power means causes said chain to move said main draft door for controlling the amount of air permitted to enter said main draft opening.
- 5. A furnace according to claim 1 wherein water is within said circulation chamber, a tap water heating device being mounted to one of said walls of said furnace housing, said tap water heating device including a coil tube extending within said circulation chamber and coupling means outside said furnace housing for connecting said coil tube to a tap water circulation system.
- 6. A furnace according to claim 1 wherein a draft adjustment means is mounted over said hole in said door, said adjustment means comprising a plate mounted over said hole for sliding movement from a first position exposing said hole to the atmosphere to a second position covering said hole and preventing air from entering said hole.
- 7. A wood burning furnace comprising:
- a furnace housing having a firebox therein, said firebox having upper and lower ends, a flue extending through said housing and into said firebox and terminating in an inner end located approximately at the vertical centerline of said firebox;
- a grate within said firebox and spaced downwardly from said upper end of said firebox for supporting burning fuel whereby the heated gases from said burning fuel will rise and exit from said firebox through said flue;
- a main draft opening in said housing positioned to provide communication of air from the exterior of said housing to the interior of said firebox adjacent said grate;
- said flue being positioned in spaced relation below the top of said firebox and above said grate so as to deflect rising partially combusted gases and thereby delay their exit through said flue;
- a secondary draft opening within said housing positioned in spaced relation above said grate and spaced relation below said flue;
- a smoke damper positioned between said secondary draft opening and the interior of said firebox to prevent smoke from exiting said secondary draft opening, said smoke damper being hinged about a horizontal axis and having a lower edge below said secondary draft opening whereby fresh air passes from said secondary draft opening below said lower edge of said damper and will mix with and be heated by said rising gases prior to the time that said gases reach said flue;
- the relative positions of said secondary draft opening, said main draft opening, said smoke damper, and said flue causing said rising gases to create a hot spot adjacent said flue, said hot spot having a temperature of approximately 1100.degree. F.
BACKGROUND OF THE INVENTION
This is a continuation-in-part of application Ser. No. 131,524, filed Mar. 18, 1980 now abandoned, which is a continuation-in-part of application Ser. No. 935,370, filed Aug. 21, 1978, now Pat. No. 4,201,185, issued May 6, 1980.
This invention relates to a means for heating water by wood burning.
Conventional wood burning stoves or furnaces generally include a firebox having a main draft for introducing air below the grate in the bottom of the firebox and additionally having a flue outlet opening adjacent the upper end thereof. The flue outlet of the prior application, Ser. No. 131,524, is at the upper end of the firebox. This location is not desirable for a water heater because the upper end of the firebox is the hottest place in the furnace, thus failing to maximize the potential heat transfer.
A problem commonly encountered with conventional wood burning stoves and furnaces arises from the fact that often the tars and other ingredients from the wood are not completely burned prior to their exit through the flue opening. This results in accumulation of tar and pitch within the flue and chimney, thereby creating a fire hazard. Furthermore, these conventional wood burning stoves and furnaces are not as efficient as they could be if not all of the wood is burned to produce heat.
Additional problems are encountered in woodburning furnaces which are used to heat water. When a water jacket is placed around the firebox of a wood burning furnace, it cools the walls of the firebox to approximately 212.degree. F. Most woods will not burn unless heated to 500.degree.-740.degree. F. and temperatures approaching 1100.degree. F. are necessary in order to provide thorough combustion of the tars and gases from the burning wood.
In the invention shown in U.S. Pat. No. 4,201,185, a baffle is used in the upper portion of the firebox to create a hot spot having temperatures of approximately 1100.degree. F. However, different problems are encountered when such a baffle is utilized in a furnace surrounded by water. The baffle becomes much hotter than the firebox walls and it buckles and often becomes disengaged from the firebox walls in response to this temperature differential.
The present invention utilizes the firebox having a flue extending approximately half way into the firebox and positioned downward from the upper end of the firebox so as to deflect and divert the rising gases within the firebox prior to their exit through the flue opening. This positioning of the flue creates a hotter firebox, burning more gases, pitch and tar, and allows less heat to escape through the flue opening, thus giving hotter water with less fuel.
Heat alone, however, is not sufficient to provide full combustion of the gases which accumulate around the flue. Oxygen must also be provided, and this is done by a secondary draft opening which is located above the grate, and which introduces air into the firebox in such a manner that the air is drawn toward the hot spot located around the flue. This oxygen facilitates the combustion of the gases which are located at this hot spot and results in more complete combustion of the gases prior to their exit from the flue. It has been found that temperatures of approximately 1100.degree. F. are achieved in this hot spot, and this temperature results in more complete combustion of gases, pitch and tar, thereby leaving a cleaner chimney with less chance of chimney fire.
In a preferred embodiment, the flue extends 121/2 inches or more than half way into a firebox having a depth of approximately 23 inches. The flue is also spaced 41/2 inches downward from the upper end of the firebox. In this position, the flue acts as a baffle, diverting the rising gases so that they mix with the oxygen from the secondary draft opening and creates a hot spot above the flue for further combustion of the gases. Also, by having the flue opening at a location other than the upper end of the firebox, there is more efficient heat transfer from the hottest area at the upper end of the firebox.
The use of a flue in the place of the baffle utilized in the air circulated furnace of Pat. No. 4,201,185, eliminates the buckling problems resulting from a temperature differential between such a baffle and water cooled firebox walls.
In order to prevent smoke from exiting through the secondary draft opening, a smoke damper is provided in covering relation over the secondary draft opening so as to cause the air entering through the secondary draft opening to move downwardly below the lower edge of the smoke damper prior to entry into the firebox.
Another advantage is obtained by virtue of the arrangement of the firebox with respect to the outer housing of the furnace. The furnace housing is spaced outwardly from the walls of the firebox in such a manner to provide a water boiler chamber around the rear, top and opposite sides of the firebox. Fresh cool water is pumped into the rear portion of the chamber and forced upward and forward through the chamber to the water outlet located on the top of the furnace. This water boiler chamber increases the efficiency of heat exchange from the firebox to the water within the boiler chamber. An aquastat is mounted within the boiler chamber to control the actuation and deactuation of the pump in response to varying temperatures within the boiler chamber. A pressure and temperature gauge and a pressure relief valve provide further monitoring of the furnace.
A further advantage is achieved by having the flue extend through the boiler chamber before entering the chimney. This permits heat to radiate from the flue into the boiler chamber where it is circulated throughout. The ventilation system thereby increases the efficient use of heat which normally would go up the chimney.
A second thermostat is provided within the boiler chamber and is connected to a main draft control which causes selective opening and closing of the main draft to control the speed with which the fire burns within the firebox.
The boiler can also be utilized to heat water for domestic hot water use. A coil tube is positioned within the boiler and may be connected to the tap lines of the building. The water within the coil is heated by the water in the boiler, thus supplementing or replacing a conventional hot water heater.
Another phenomena attained with the present invention is that extreme heat is attained inside the flue. This causes further burning of the tars, pitches and gases so that the inside of the flue remains much cleaner than with other prior wood burning furnaces.
Therefore, a primary object of the present invention is the provision of an improved means for heating water by wood burning.
A further object of the present invention is the provision of a wood burning furnace which causes more complete combustion of wood and the tars within the wood prior to the exit of the combusted gases through the flue opening.
A further object of the present invention is the provision of a means which minimizes the accumulation of tars and other impurities in the flue opening so as to minimize the fire hazard therein.
A further object of the present invention is the provision of a means which maximizes the heat achieved per unit of wood burned therein.
A further object of the present invention is the provision of a means which maximizes the heat exchanged between the firebox and the boiler chamber containing the water to be heated.
A still further object of the present invention is the provision of a means which provides a secondary draft opening for providing oxygen to the upper interior portion of the firebox.
A further object of the present invention is the provision of a means which prevents the exit of smoke through the secondary opening while at the same time permitting the entry of air through the secondary opening so as to provide oxygen and improve the combustibility of the gases within the fire chamber.
A further object of the present invention is the provision of a wood burning furnace which causes extreme heat in the area inside and outside the flue so as to more completely burn gases, pitch and tar and thereby minimize creosote build-up in the firebox, flue and chimney.
A further object is the provision of a furnace which permits maximum temperatures within the firebox to reach approximately 1100.degree. F. even though the walls of the firebox are being cooled to approximately 212.degree. F. by the water surrounding them.
A further object of the present invention is the provision of a device which is economical to manufacture, durable in use and efficient in operation.
US Referenced Citations (18)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 513859 |
Feb 1921 |
FRX |
Non-Patent Literature Citations (1)
| Entry |
| "Woodland F-20 Fireplace Stove" in Woodstove Fireplace and Equipment Directory, vol. III, 1980, Copyright 1979 by Energy Communications Press, Inc., Manchester, NH, p. 109. |
Continuation in Parts (2)
|
Number |
Date |
Country |
| Parent |
131524 |
Mar 1980 |
|
| Parent |
935370 |
Aug 1978 |
|
Patent Grant
4461242
