Wood Burning Hot Water Furnace

A great variety of wood burning stoves have been developed over the years and these frequently include large insulated water storage tanks which require substantial inputs of energy to raise the temperature of the water. A number of prior art patents embody the large volume storage tank concept such as:

The present invention embodies a high temperature combustion system which transmits extremely hot combustion gases to a relatively low volume of water circulated through the water jacket. The furnace unit provides a forced combustion air supply system which is transmitted to the fire box containing wood to be burned and which is transmitted through a heat exchange path into the fire box to provide pre-heated combustion air to the fire box. The fire box construction provides an exhaust air distribution plenum at the bottom of the fire box. The hot exhaust gases produced from the burning fuel pass down into the bottom exhaust gas plenum and out through the exhaust passage and stack. As soon as the supply air from the blower reaches the combustion chamber, the intensity of the heat of the exhaust gases from the burning fuel is increased to rapidly heat the water being circulated through the water heating chamber. This is accomplished without destroying the metal used in the construction of the combustion chamber.

The combustion air is provided by a blower and travels upwardly through the combustion air supply passage through a plurality of openings formed in the inner shell to supply a flow of combustion air to the lower portion of the combustion chamber.

A water jacket surrounds the lower portion of the combustion chamber and is formed by two spaced apart bottom panels or plates. A bottom exhaust discharge passage extends downwardly from the combustion chamber through the space between the two bottom panels to discharge the exhaust gases downwardly into the exhaust plenum below the water jacket in heat exchange relation to the jacket.

FIG. 1 is a central vertical sectional view through a furnace embodying this invention.

The furnace shown in FIG. 1 is designated as an entirety by the letter A. The furnace illustrated is a generally cylindrical unit having a combustion chamber 9 within a cylindrical inner shell 10. A water heating jacket or chamber 12 surrounds the inner shell 10 and is defined by an outer chamber wall 14 spaced from the inner shell 10 and surrounding the same. An annular exhaust gas passage 16 surrounds the wall 14 and is defined on the outside by a generally cylindrical exhaust passage wall 18. Insulation 20 is provided around the outer wall 18. An annular combustion air passage 22 surrounds the exhaust chamber wall 18 and communicates with the inner combustion chamber 9 through a plurality of vent conduits 22a and inner openings 22b.

The combustion gases from chamber 9 are forced downwardly through a central exhaust discharge passage 9a into a bottom exhaust gas plenum 18a communicating with the bottom of the annular exhaust gas passage 16.

An insulated hinged cover 24 is provided to close the top of the combustion chamber 9 and has a pivoted latch 24a. A blower 25 supplies air into the combustion chamber 9 through the annular passage 22 and openings 22b. The water to be heated is circulated through the chamber 12 by a suitable pump (not shown) and travels from inlet 12a up through the chamber 12 and out through the discharge 12b into conventional heat exchangers within the building environment to be heated (not shown). A clean-out opening 26 communicates with the exhaust chamber plenum 18a and is provided with an access door 26a to permit any ash accumulation to be removed from plenum 18a. The exhaust gases pass upwardly through the annular passage 16 and out through the stack 16a to the atmosphere.

The temperatures produced within the lower portion of the combustion chamber where the combustion air enters the chamber reaches 1500 to 2000 F. The extremely hot exhaust gases pass directly from the hottest area of the combustion chamber downwardly through the exhaust passage 9a in the bottom of the chamber so that the area of the water jacket in the bottom of the furnace is subjected to maximum heat on both sides thereof to provide almost instantaneous heat response in the water supply and the environment to be heated. Ash from the wood being burned builds up an agglomerated semi-solid mass in the form of an inverted conical ash residue 9b around and the central discharge opening. This inverted conical ash residue mass forms an insulating cone which protects the lower inside wall of the furnace below the air inlet openings in the same way that refractory brick might protect a furnace wall and eliminates the need for the use of such refractory material in the bottom of the furnace. Due to the intensity of the heat, very little ash is actually produced from the wood being burned and the hottest gaseous products of combustion travel downwardly through the exhaust discharge passage 9a into the plenum 18a thus exposing both sides of the bottom of the water jacket to maximum heat during operation of the blower. The intense heat within the combustion chamber 9 dries out the wood supply located in the top of the chamber so that ever green or wet pieces of wood can be used effectively in the furnace unit. As soon as the blower is shut off either manually or by a thermostat (not shown) in the controlled environment, the limited air supply reduces the combustion level so that the wood supply is preserved for 18 to 20 hours in a furnace unit smaller than 3 feet in diameter by 4 feet in height. Also, the furnace can be shut off for 15 to 18 hours and still retain sufficient sparks to ignite when the forced combustion air is provided when the blower is turned back on.

This invention provides a relatively compact yet highly efficient wood burning water heating furnace which eliminates the need for a large volume heat storage tank and which is designed to produce extremely high temperatures with only a minimum of residue ash.