It builds up in the draft door area, not bad, but enough can make the flipper stick. 30-40° range you'll get 24hr burns, below that 12 hrs easy. I would like to point out also, all my wood was cut at 18" because I had the wood piled up before the decision was made to purchase the owb. Noting that, the firebox was NEVER filled to capacity at those burn times. Longer pieces will mean more wood equaling more than sufficient capacity at really cold conditions. One day last January, it was below 0° with 30+mph winds I threw a few chunks in at noon. ( I also added some to neighbors woodmaster) I was right about 14 cords last winter, was about what the neighbor used, too, new house, 30x40 barn, and no dhw. We were watching each others piles quite close, lol, seeing how the stoves compared to each other. In my opinion, they are both good units, there's not much difference, other than price and his has a draft fan. They both gave us the heat we called for on roughly the same amount of wood. I would definitely buy the ridgewood again. BTW, mine is still burning for dhw, I can't believe how little wood it is operating on for that! The wife and two teenage daughters like long hot showers.