Drying lumber is the highest operational cost for sawmills, and those mills should be able to closely estimate that cost. Cost estimation is important for those mills that are thinking of changing from one energy source, such as natural gas, to another energy source such as wood hogged fuel: sawdust, trim ends and bark. Different sources of energy, such as natural gas, electricity, propane and wood, can be compared using their heat content. In the US, the most common measure of heat content is the British thermal unit (Btu). One Btu is the amount of energy needed to raise the temperature of one pound of water one degree Fahrenheit, and at sea level it takes 1,000 British thermal units of energy to evaporate one pound of water. Based on this information, an Excel spreadsheet was developed to help sawmills estimate their drying costs. This paper will discuss how lumber drying costs are estimated and how a mill can compare costs of using one energy source versus another.