Wood And  It's  Properties

All wood has moisture.  Kiln dried lumber in the central Indiana area has a 19% moisture content, air dried firewood which has been covered or stored inside has no less than a 30% moisture content.  So, for every ten pounds of wood you burn, there is at least three pounds of water steamed out of the firewood.

Wood takes between six to nine months after it has been cut and split before it is seasoned, as it dries from the ends toward the center.  Even if the log has been laying for a while, it still needs 6-9 months before it is ready to be burned in your system.  I always try to have at least two rick (or one fourth yearly consumption) of wood left from the previous year to begin the new winter with.  That way the wood I get in the summer has had time to season before I have to start using it. Get all the wood you'll be needing during the summer, if you just get a little bit at a time during the winter, I can promise you it will be picked up off the wet ground and not have been covered.

Stack your firewood as you get it, so the air can circulate through it to maximize the drying time. Also stack the wood (bark side down) on something to keep it off the ground.  I use wooden pallets, but iron pipes, 4x4's, bricks, concrete blocks, etc. can be used.

Be sure your firewood is covered by September.  That way it will stay dry when the Fall rains begin.  As the outside temperatures get cooler, it takes longer for it to dry again.
I use those plastic-nylon tarps and milk jugs filled with water tied to the grommets to hold them down.

Why all the hype on dry?

When you add a piece of wood to an existing fire, the wood absorbs heat, driving out moisture.  I'm sure you have seen water and steam bubbling out the ends of a stick of wood. As the moisture escapes, more heat is absorbed allowing the wood to break down into gases.   These gases (smoke) become hot,  producing the flame we see as the wood burns.  If you look closely you will see the flames just above the piece of wood.

Now as these gases, smoke, and moisture escape up and out your flue, they begin to cool off.  At any point your system is below 250 degrees the moisture or steam will begin to condense, just like sweat on an ice tea glass.  The smoke and other unburned gasses cling to the moisture forming creosote.  The bottom line is  the wetter or greener the firewood, the cooler your flue will be, creating more creosote.