Firewood for a wood-fired oven is generally divided between two broad categories: hardwood and softwood. Hardwoods come from deciduous, broad-leafed trees; softwoods come from needle-bearing coniferous trees. Firewood is sold by the cord, which equals 128 cubic feet and measures 4 by 4 by 8 feet.
Use only seasoned, dry hardwood in your pizza oven. Hardwood is usually denser and less resinous, producing a fire that is hotter and cleaner than softwood. Buy from a dealer or get free wood from friends and neighbors who are pruning their trees or ask owners of vacant lots being cleared. You can also try asking your local Parks & Recreation for free wood.
Use hardwood such as; Ash, almond, avocado, beech, birch, oak, fruitwood (cherry, peach, plum), walnut, hickory, olive, maple, pecan, mesquite. Avoid the use of resinous wood such as pine or spruce.
Fresh cut wood or green wood has too high of a moisture content to be of any use to you cooking. In six months of reasonable weather (evaporation depends on temperature and humidity), the seasoning is complete; in two years the wood is as dry as it will get. Wood will dry faster if it is split. Seasoned wood will have cracking on the ends of the logs and will be dull in color. Smack two pieces together, a ‘thud’ sound indicates the wood is green, a ‘thunk’ indicates dry wood.