You should never burn unseasoned wood in a fireplace or even in a regular enclosed wood burning stove because doing so will cause dangerous creosote build up in your chimney or chimney pipes and can start a chimney fire.
Also unseasoned wood will be hard to light and keep going. You need to wait at least 6 months for most wood to season enough to burn properly in a fireplace or wood burning stove.
Seasoning firewood for at least a year is better though and you'll notice the difference in the heat output and BTU'S from the year seasoned firewood vs the 6 month seasoned firewood.