Friend and I are playing with the idea of a chips only OWB. He and I burned some chips last winter along with all the froth? from the splitting operation. As long as I didnt get too carried away with the amount thrown in it worked fine. If I put too much in at once it would leave a layer unburned until stirred and smoke was heavy. My boiler has "over fire air injection" in other words it blows in the door over the fire. His OWB injects air up through grates and he could burn a larger percentage of chips vs chunk wood. Moisture percentages will affect the deal too. I own a chipper so the chips were dry, at least as dry as the wood was. We tried some chips from the county yard waste dump and being wet and half rotted they didnt work very well at all.