I bring this up because of correspondence with a Hearth member here who recently purchased a Lambda controlled gasser and is anticipating the addition of 2000 gallons of storage. Let me say at the outset that I do not disparage his choice in any way. I questioned why not just go with a Garn and he cited the "technology" of the boiler he purchased. While I don't disagree that the boiler he chose is a very good product, I think there is a fundamental disconnect in the thinking that high tech controls and O2 sensors are required to obtain hydronic nirvana. I would humbly submit for discussion here, the premise that storage and dumping all the heat from a wood load into such, is a much more hassle free method of obtaining superior efficiency and reduced emission levels. Recent tests have shown that even with very high quality, O2 controlled units emission levels rise dramatically and efficiency drops when these units are subjected to low load situations. As any astute person here is aware, full boiler output is needed less than 5% of the heating season. That being the case, our heating systems are subjected to operation at less than full load for the majority of the winter. The person I referenced above is doing it right by adding significant storage that will allow flat out burns until all the fuel is consumed under most circumstances. He will likely not have any issues other than the routine maintenance/replacement required with any lambda (O2 controlled) system. Using numbers [shown below] from a test on a production Garn 2000 using cordwood (not the faulty EPA test), you can see that efficiency and emissions from a good basic unit that burns the entire load of wood and does not idle are such that there is virtually no room for realistic improvement. For those who are unfamiliar with it, the Garn is a 30 year old design that was done right in the first place. It uses no controls other than operator input and a button to start the combustion fan when fueled. The test was conducted by Intek in accordance with the Thermal Storage Appendix XI of ASTM Document E 2618 â€“ 09, using oak cordwood just like you and I burn rather than the kiln dried cribwood in the EPA protocol. It was done at the Garn facility using a standard dilution tunnel sampling method and it gave the following results. 88.4% delivered efficiency and more tellingly, only .088 lbs of particulate/million BTUâ€™s delivered output. This emission result is 72% less than the current EPA Phase II Limit of .32 lbs of particulate per million BTUâ€™s delivered. For the sake of clarity, it should be noted that wood heating efficiency is currently based upon the lower heating value of fuel industry wide. The efficiency achieved simply physically cannot be any better or a person would encounter issues with condensation of flue gas and the resulting disaster in your heat exchanger. So I would ask the following question; is "the answer" simply storage and good design, or are high tech controls going to be the best long term choice? I tend to fall into the KISS category but I am willing to learn if I'm missing something here. Let's hear what you think.