Low emission, wood fueled hydronic heater

Abstract

A wood burning hydronic heater comprises a primary firebox into which the wood is loaded and wherein initial combustion occurs. The heater also includes a secondary combustion chamber below the primary firebox into which the combustible gases from the primary firebox are forced and into which a fresh air stream is passed to burn the gases. A primary heat exchanger downstream of the secondary combustion chamber is adapted to reduce the temperature of the exhaust exiting from the secondary combustion chamber. A catalytic combustor, located in a chamber downstream of the secondary combustion chamber and primary heat exchanger, completes combustion and reduces emissions.

We claim: 
     
         1 . A wood burning hydronic heater comprising:
 a primary firebox into which the wood is loaded and wherein initial combustion occurs;   a secondary combustion chamber into which the combustible gases from the primary firebox are directed and into which an air stream is passed to burn the gases;   a primary heat exchanger downstream of the secondary combustion chamber adapted to reduce the temperature of the exhaust exiting from the secondary combustion chamber; and   a catalytic combustor located in a chamber downstream of the secondary combustion chamber.   
     
     
         2 . The heater of  claim 1  further comprising a secondary heat exchanger that extracts heat from the exhaust gases such that the exiting stack temperature of exhaust gases is about 250° to 300° F. 
     
     
         3 . The heater of  claim 2 , wherein the catalytic combustor is located in a chamber between the primary heat exchanger and a secondary heat exchanger. 
     
     
         4 . A wood burning hydronic heater comprising:
 a primary firebox into which the wood is loaded and wherein initial combustion occurs;   a secondary combustion chamber below the primary firebox into which the combustible gases from the primary firebox are directed;   vertical channels providing fluid communication between the firebox and the secondary combustion chamber below the firebox;   an air blower; and   a brick combustion plenum disposed between the primary firebox and secondary combustion chamber, the brick combustion plenum having an upper channel and a lower channel, wherein the upper channel forces air into an upper portion of the primary firebox and the lower channel forces air into the vertical channels.   
     
     
         5 . The heater of  claim 4  further comprising downwardly inclined slots that pass air from the lower channel to the vertical channels. 
     
     
         6 . The heater of  claim 5 , wherein the downwardly inclined slots act as nozzles to introduce air at a downward angle for combustion in the secondary burn combustion. 
     
     
         7 . The heater of  claim 5 , wherein there are four vertical channels. 
     
     
         8 . The heater of  claim 5  further comprising a pair of side airflow paths on each side of the firebox in fluid communication with the lower channel to pass air to each side of the firebox. 
     
     
         9 . The heater of  claim 5 , wherein the primary firebox has a floor constructed of arranged bricks, the vertical channel formed in a brick forming the floor of the primary firebox. 
     
     
         10 . The heater of  claim 9 , wherein the bricks further comprise the downwardly inclined slots formed in each that pass air from the lower channel to the vertical channels. 
     
     
         11 . The heater of  claim 4 , wherein one of the bricks between the primary firebox and the secondary combustion chamber has a horizontal channel forming a horizontal airflow path with the lower channel. 
     
     
         12 . The heater of  claim 4 , wherein the primary firebox has a floor constructed of arranged bricks, and one of the arranged bricks has a horizontal channel extending along the length of the one of the arranged bricks to provide for fluid communication with the lower channel to allow air to flow to each side of the firebox. 
     
     
         13 . The heater of  claim 1 , wherein the emissions from the heater is less than 0.32 pounds particulate per 1,000,000 BTU output. 
     
     
         14 . A wood burning hydronic heater comprising:
 a primary firebox into which the wood is loaded and wherein initial combustion occurs;   a secondary combustion chamber into which the combustible gases from the primary firebox are directed and into which an air stream is passed to burn the gases;   a primary heat exchanger downstream of the secondary combustion chamber adapted to reduce the temperature of the exhaust exiting from the secondary combustion chamber;   a catalytic combustor located in a chamber downstream of the primary heat exchanger; and   a secondary heat exchanger located downstream of the catalytic combustor that extracts heat from the exhaust gases such that the exiting stack temperature of exhaust gases is about 250° to 300° F.   
     
     
         15 . The heater of  claim 14  further comprising an air blower in fluid communication with the primary firebox through an air opening in a rear wall of the primary firebox and a removable firebox air channel mounted to the rear wall of the primary firebox by a pair of brackets, whereby air is introduced into the primary firebox via the air blower into the rear of the primary firebox through the air opening in the rear wall, upwards through the air channel and out the exit opening into upper portion of the primary firebox. 
     
     
         16 . The heater of  claim 15 , wherein the air channel comprises a flat rectangular steel stamping formed into an open box having a closed bottom end and an upper end, and an exit opening and tab disposed at the upper end; and wherein one of the pair of brackets is located just below the air opening and is shaped is snuggly accept the closed bottom end of the air channel and the other one of the pair of brackets is situated above the air opening and is shaped is snuggly accept the tab. 
     
     
         17 . A method of reducing the smoke emissions of a wood burning hydronic heater, the method comprising the steps of:
 providing a primary firebox into which the wood is loaded and wherein initial combustion occurs;   providing a secondary combustion chamber into which the combustible gases from the primary firebox are directed, during which an air stream is passed to burn the gases at extreme temperatures to maintain high combustion efficiency;   directing the combusted gases to a primary heat exchanger to reduce the temperature of the exhaust to a temperature suitable for use with catalytic combustion; and   directing the exhaust gas to a catalytic combustor located in a chamber downstream of the primary heat exchanger.   
     
     
         18 . The method of  claim 17  further comprising the step of providing a secondary heat exchanger that extracts heat from the exhaust gases such that the exiting stack temperature of exhaust gases is about 250° to 300° F. 
     
     
         19 . The method of  claim 18 , wherein the catalytic combustor is located in a chamber between the primary heat exchanger and a secondary heat exchanger. 
     
     
         20 . The method of  claim 19 , wherein the emissions from the heater is less than 0.32 pounds particulate per 1,000,000 BTU output.