At what moisture level does wood begin to become less efficient for burning?

Wood begins to become less efficient for burning at a moisture content above 20%. When wood has a higher moisture content, it contains more water, which means that a significant amount of heat energy must be expended to evaporate that moisture before the wood can ignite and burn effectively. This excess moisture reduces the overall energy released during combustion, resulting in smokier fires, less heat production, and more creosote buildup in chimneys.

As the moisture content rises above this threshold, not only does the efficiency decrease, but the likelihood of incomplete combustion increases, leading to increased emissions and pollutants. Therefore, for optimal burning efficiency and heat production, wood should ideally have a moisture content of 20% or lower. Properly seasoned wood, which typically falls within this range, burns hotter and cleaner, making it the preferred choice for heating purposes.