Today, July 10, my family and I took a trip to western New York state to visit the Brocton factory of Dunkirk Metal Products. This is where their line of wood gasification boilers is produced. Alternative Fuel Boilers, LLC has been mentioned in earlier posts in this thread. I noted that we were contemplating the model EBW-100, a 100,000BTU unit. As with European style gasification boilers, peak efficiency is reached by maximizing the time that the boiler spends in the “secondary combustion” stage for a given load of wood. This necessitates the use of a large hot water storage tank to soak up the excess energy from the boiler beyond what the house currently needs so that heat can be later drawn from the tank as needed. This also greatly simplifies the addition of a domestic hot water loop and even a supplemental solar loop.
The control system of the EBW-100 however allows this particular boiler to be used in a tankless system as well, making it essentially a drop-in replacement for our current oil fired boiler. Once heat demand for the house has been satisfied, the combustion air blower shuts down and the fire dies back. The ceramic refractory retains its heat so when heat is needed again the boiler relights almost instantly (provided there is sufficient fuel remaining) when the fan is restarted. While somewhat less efficient than the system with storage tank, it’s still much better (and cleaner) than the typical outdoor wood furnace. Plus, all heat that does not go up the flu ends up dissipating into the house.
We still have not solved the storage tank issue, and it’s starting to look like this might be a custom project all unto itself. But it’s nice knowing that it can be added later and we can build the system in stages rather than trying to do it all at once.