I have enjoyed reading all of the questions and answers that you all have. I have in my past worked for a company that builds wood gasification systems called Chiptec. The systems are used in schools and saw mills, mostly anyone who has axes to wood waste. The systems that Chiptec builds range in size from 1 million to 50 milion BTU. ( Big Boys ) At the school where I work we burn wood chips in a gasifire. ( 3 million BTU unit, 90hp ) If we burn oil it cost us 350.00 a day to heat, and if we burn wood chips it cost 100.00 a day to heat the school. And no smoke from the wood chip system. I am a steel fabricator and I am building a wood gasificator that I will weld right to the side of my Franks boiler. This unit is the same size as my wood boiler. It will be a down burn. The gasifire will be lined with refractory. ( bottom, sides and top ) To get true gasificaton you need refractory. So here is my question I am not sure what size the secondary air nozzle needs to be in the refractory. Like 1" by 8" long? My gasifire look a lot like the Econoburn. Can anyone tell me what size the opening is in the refractory that is called the nozzle.