You can safely burn moldy wood

Mold stains & mold in the firewood - a problem?


What is blooming in the firewood?

The work is done, the good firewood for the season after next has been carefully piled up and stowed away. But after a few weeks the logs slowly start to mold more and more. At this point, many stove owners ask themselves, “Did I do something wrong? - Where does the mold in the firewood come from? - Is the mold in the firewood a health problem? Does mold in the wood reduce the heat output? ”This article aims to provide some answers to these and similar questions. So don't give up yet and keep reading. :-)

Why does mold develop in the firewood?

Mold always needs 3 components to grow.

1. Lots of moisture
2. Nutrients
3. Standing air

Sure, freshly felled firewood contains a lot of moisture (often 40% and more of the total weight of the wood) and therefore fulfills the first point in our list very well.The logs also contain nutrients for mushrooms in abundance. The fungi metabolize the cellulose contained in the wood in order to obtain their energy for growth and spread. And last but not least, the crucial point 3 comes from the list - the still (or little agitated) air. Logs that are freely stored in the open are (if at all) colonized by fungi only for a short time. In order to be able to grow undisturbed, mushrooms need stagnant air and as uniform climatic conditions as possible.

What can be done against mold in the firewood?

Firewood should always be stacked so that air can circulate around it. This means that all sides of the wood store are open and should not be covered with impenetrable tarpaulin or similar materials. A few stands and a simple canopy on the south or east side of the house are ideal locations for firewood storage if you want to avoid mold in the firewood. It does not matter whether driving rain occasionally moistened the wood. The moisture dries off quickly and is only slightly absorbed into the wood.

Basement rooms, on the other hand, are in almost all cases unsuitable for storing fresh firewood, as there is no air circulation here. Mold in the wood is usually preprogrammed here.

Is the mold in the wood dangerous to health?

As a rule, mold growth in the firewood is completely harmless to healthy people. This applies to both handling (sawing, chopping, stacking, etc.) and burning in the stove. Caution is only required when known Allergies to mold are present or cause respiratory problems such as asthma. In this case, inhalation of the mold spores should be avoided with a face mask. When buying a face mask, please make sure that it is also suitable for keeping out the tiny mold spores. Protection class P2 masks should be sufficient in most cases.

Does mold reduce the heating performance of firewood?

It depends…...
If, as described above, the firewood has been stored completely fresh and the wood "blooms", a short-term infestation is not a problem. With open, airy storage, the moisture content in the wood decreases quickly and the fungi stop working again within a few weeks. The calorific value is retained.

However, if the fungi have years to spread undisturbed because the moisture in the wood cannot escape (or new ones are added regularly), the wood will gradually decompose completely. The wood smells musty / earthy, Beetles have also settled in the wood and the logs become brittle or crumbly. The calorific value of such damaged wood is greatly reduced and does not bring much heat into the house.

When buying firewood, you should always make sure that no foxing spots are visible in the firewood. Here it can be assumed that inferior wood is offered that should only be bought at a very low price. If you are not sure about the quality of the firewood you are buying, you better refrain from buying it and go to the nearest dealer before you get annoyed for months about the inferior wood in the stove.

Do the break test.
If possible, just take a branch of hardwood about 1m long and about as thick as forearm that you fear an infestation of microorganisms, take hold of one end and then hit the other end vigorously on a hard surface (concrete, asphalt, etc.). If a branch is not the reason for a break, this branch should withstand the blow without any problems. If it does not do this and breaks off with a blunt-jagged break edge, the branch is likely to have been damaged by fungi and microorganisms. Softwood may break without damage, so the test can only be used to a limited extent here. However, the broken edges of healthy softwood are much more pointed and jagged than those of damaged woods.

Further interesting information on the subject of mold and mold control can be found on the website of There you will find out in detail what can be done in the event of mold infestation in the house and apartment and when, in any case, a specialist should be called in to assess and remediate the mold infestation.

Good luck with buying and drying your firewood!