HOW IT WORKS
   This boiler is the result of an extensive R&D project completed over thirty years ago. First we discovered that the heavier tars and creosotes start burning above 1200 and steel starts to break down at 800. This is the reason steel wood stoves burn dirty and do not last long.  If you surround the fire with a steel fire box and water you remove the combustion heat before it reaches the temperature necessary for a clean burn. We burn the wood in a six inch thick refractory fire chamber surrounded by three inches of high temperature insulation and an airtight steel skin. The fire box temperature exceeds 1800 and the skin temperature is less than 100. Then we use a water tube pressure vessel to remove both radiant and convective heat. The heat must travel down past the vessel to the exhaust port heating the incoming combustion air on the way. The exhaust temperature is below three hundred degrees.  Once the fluid reaches the set temperature the draft is closed and the fire is completely extinguished, it does not smolder. Because the thermal mass in the refractory stays above the flash point the fire always re-ignites when the boilers calls for heat again.
The Seton Wood Boiler has unique features that make it better than any other wood boiler.
   First is the refractory combustion chamber that ensures a very high combustion temperature and a long flame path with enough turbulence to complete the burning of all gases. Once the wood gases are completely burned the hot gases enter the heat exchange area .
   The heat exchanger is a down draft system with the exhaust exiting where the cold water is coming in. This increases the deferential between the water temperature and the exhaust temperature which lowers the exhaust temperature and increases the thermal transfer efficiency. The draft air is heated with the exiting exhaust gases after all the available heat is put into the water which increases the combustion temperature without taking heat from the combustion process.
   The heat exchanger or boiler, is a water tube design which absorbs more heat per square inch than fire tube boilers, withstands much more pressure and also holds much less water so it responds quicker. Because of the very limited water storage water tube boilers are much safer than fire tube boilers.
   Do not confuse downdraft heat exchangers with down draft combustion. Down draft combustion is where the flames are drawn down into a combustion chamber. Horizontal combustion chambers in downdraft boilers have a problem with the hot gases layering. For these to burn cleanly they would need to be much longer and have more turbulence or a swirling action. Although downdraft combustion does burn cleanly when working properly the ashes are drawn down into the combustion chamber and are exited out with the exhaust contributing to particulate air pollution. The fire tube boiler section is updraft and cannot achieve nearly the efficiency of a downdraft heat exchanger because the exhaust gases are exiting next to the hottest water in the boiler.

The Seton Boiler design requires several things to work properly. During a power outage the draft will close, damping the fire down, there should be two relief valves on top of the boiler, one thirty pound pressure relief and one 120 degree T&P. Also a very critical thing is a check valve behind the relief valves, this causes the cold fill water to rout from the fill valve on the back of the boiler up through the pressure vessel. In my opinion, the new Greenwood will have a short life because of the straight tube design. Each tube will have a different expansion rate and will put a great amount of stress on the headers. Every water tube boiler built uses a bent tube design for this reason.