So, I did a little reading on firewood, this is what I found to be the general consensus among those who use firewood as their primary fuel source.
There are some woods and plants you should never burn indoors. Softwoods, ie evergreens, conifers and soft deciduous like Larch. They burn too fast and produce excessive smoke containing soot and creosote that can cause chimney fires. Softwood may be burned outdoors in open pits for heat but should not be cooked over.
Under any circumstance, do not burn pressure treated lumber, any plant or tree that has the word poison in it's name, poisonous plants that don't have poison in it's name, like foxglove or oleander. Driftwood contains a surprising amount of toxins. Rotted wood will off-gas mold, mildew and bacterial toxins.
Green wood, aka unseasoned firewood, contains a lot of water and sap. It will not burn efficiently, the fire will not get hot enough to produce complete combustion. The byproduct of incomplete combustion is excessive soot and smoke. Green wood will also hiss, snap, crackle and pop more, increasing the risk of throwing glowing embers out of the fire.
Firewood should be seasoned for a minimum of six to nine months. The best time to split wood is during winter months when the air is driest. Logs split in humid seasons will retain, or even absorb moisture and are prone to fungus and mold growth.
The ideal length for logs is 18 inches, and logs greater than 12 inches in diameter should be split into pieces no smaller than 4 inches in diameter. Larger logs are cut and split so that they will fit into a stove, fireplace or pit. The length and diameter of split wood is subjective and dependent on the application.
Some degree of uniformity in length and diameter helps with regulating burn rate. Processed firewood is typically 4-6 inches in diameter. Fatter logs may be used for longer overnight burns, conversely, thinner logs are used to make a very hot fire for boilers and other high heat applications such as blacksmithing.
Now, the question of the day; To split, or not to split? Un-split logs are known as "rounds". Depending on the size of a fireplace or fire box door, rounds may be as wide as 12" in diameter. Rounds have less surface area, so they do not burn as fast. Rounds in the 4 to 6 inch range are generally preferred over split wood in the same size range. Whether or not to split an 8-12 inch round is a matter of preference.