It does not matter what kind of wood you burn: as long as it is really, truly seasoned. In the case of hardwoods, especially oak, they must be seasoned for over one full year! That means last year's wood - NOT this years wood! If you're wondering about which wood is really the best, or what causes the least creosote to build up, the answer is the same! Properly seasoned wood produces the most heat, and produces the least creosote! It's not the kind of wood you burn that makes the difference, but whether or not the wood is seasoned. Firewood that hasn't been split for over a year isn't worth a darn! On the other hand, dry well seasoned wood is just great! Seasoned wood burns hot and clean.