Here’s a good example why you should not burn wet (green) firewood. This wood I had set aside out in the field, air drying for about 8-9 months. Maple wood mostly. Most people think that a year or less is all that’s needed to “season” firewood.
While yes, it does dry some, its not yet ideal for burning. Wet wood contains a lot of water obviously. To boil off that water requires BTU’s that would otherwise have been created to produce heat. Yes, the wood still produces warmth, but its not optimal. So to get the most of your investment, consider purchasing your wood a year in advance.
There’s also the issue of creosote build up in your chimney. There is plenty of reported evidence and studies that indicate wet wood produces colder temperatures inside the chimney and as a result allow creosote to adhere to the chimney surfaces.