It depends on who you talk to. I think OWBs get scapegoated for a lot of pollution caused by woodstoves and other types of wood burners--both older units and newer ones being operated incorrectly. Or indoor boilers and furnaces, which are exempt from EPA regs. It's just they're not parked in the backyard where everyone can see them. One big problem with OWBs is one of their big selling points: You can burn anything in them....and people do. But the facts are these: Gasifiers burn about half as much wood for a comparable amount of heat; They're two to three times as efficient as an OWB as a result; They make no visible smoke or smell when operating. BUT..... They need very dry wood to work properly; They cost more than most OWBs; Setting them up right is more complex and expensive than a typical OWB installation; They tend to go inside the house, which can have insurance implications Some companies are making outdoor gasifiers which aren't cheap, but I think they work pretty well if you feed them dry wood. So if efficiency, smoke and wood supply are not your big concerns, go with an OWB. If they are, then you should seriously consider a gasifier. It's as simple as that in my book.