Burning wood causes combustion, and a byproduct of combustion is H20, or water. When you burn wood, the moisture in the wood is changed to a gaseous state (vapor) and mixes with the creosote that is formed from burning wood. This mixture rises up the chimney , cools, and solidifies. To prevent creosote buildup in your lined chimney, be sure that your stainless steel liner pipe is insulated.
This is the basis for creosote build up. The cooler a chimney is while a fire is burning, the greater the amount of solidified creosote on the inside of the flue system. An insulated stainless steel chimney pipe allows the flue system to stay warm enough to prevent an excessive level of precipitation in the stainless steel liner. The insulation encourages the vapor and caustic byproducts of combustion to rise up and out of the fireplace itself.