The Ooni Fyra and Ooni Karu are both pizza ovens capable of burning wood, however unlike the Ooni Karu that burns hard wood, the Ooni Fyra has a wood pellet burner instead. The benefit of wood pellets is they are easier to load and keep burning than traditional hard wood. In fact, if you're only planning to burn wood in your Ooni, I recommend the Ooni Fyra 12 over the Ooni Karu 12 due to its lower price and superior gravity fed pellet hopper design.