Wondering if any other Tarm Solo owners have any thoughts on this. I originally installed the coal grates and firebox reducer with intent to burn coal but then decided to burn wood. The stack temperature is considerably higher with the wood grates as opposed to the coal. It seems to me that the extra "loop" provided by the reducer holds heat longer in the boiler thereby making it more efficient. Of course, this is just my theory but I seem to burn less wood with the coal grates than with the wood ones installed. On the downside the slower burn may intensify the creosote problem, somewhat.