Rotten and Moldy Firewood in the Fireplace: How to Spot It and What to Avoid
German agricultural portal agrarheute notes that firewood burns well only once its residual moisture has dropped to about 15–20 percent. Moldy logs should not be burned, because spores spread through the room.
Owners of fireplaces and stoves in Germany should pay attention to the quality of their firewood. According to the German agricultural portal agrarheute, wood generally burns well only when its residual moisture has fallen to roughly 15 to 20 percent. This matters for anyone who heats with wood, since poorly stored logs can become unsuitable for burning and harmful to health.
How mold develops
If firewood is stored too damp for a long period, fungi can form and change the wood's appearance. Musty spots on the logs point to mold. High humidity and still air encourage it. Mold can appear within a few weeks to months.
Black lines or slight discoloration put many people off, but on their own say little about burning quality. The problem begins when the wood visibly loses substance.
Why moldy wood is unsuitable
Moldy firewood does not belong in the fireplace. When it is carried and burned, spores spread throughout the room. Allergy and asthma sufferers quickly reach their limits, and the spores are harmful to healthy people as well.
How to protect firewood
Storing logs in a dry place with good ventilation protects them from fungal infestation. If the infestation is only moderate, individual logs should be sorted out and discarded.
There is no blanket rule for when wood is too old. It depends on the species: oak and black locust take longer to dry and are more resistant to weather, while spruce dries faster but is more sensitive to moisture. Storage conditions are decisive for the quality of cut wood.
