How much mold on firewood is too much to burn?

by Jonathan


Reading your page on moldy firewood was very interesting and helpful, thanks. I have one question. You say:

"For home heating purposes, taking a pice of firewood with a little bit of mold on it and placing it directly into a wood stove, wood furnace or fireplace is acceptable as long as the wood is dry."

How much mold is a little bit, and how much would be too much to burn? Our stacked firewood, which is only a couple of months old and still drying, has mold on many of the cut ends (but I see almost none on the sides of the logs). In some cases the mold covers pretty much all of the surface of the cut end. These two photos are among the worst of them.

Some of the wood is stored inside a shed, and this has more mold than the wood stored outside. Unfortunately it's all stored on the north side of the house and doesn't get any sun (we are beginners and didn't know).

Thanks a lot!



The amount of mold you have growing on your firewood should not be a problem to burn (keep in mind that people with Asthma or other health problems could be more sensitive to mold).

However, if the firewood has only been drying for a few months it's probably not fully seasoned and it's still to wet to burn efficiently.

I would guess the logs inside your shed contain the most mold because they did not have enough sunlight or most importantly air flow to dry. Don't worry, it takes a few years of burning firewood to figure things out. Next year you can either move your wood storage area to a sunnier spot or make sure the wood inside the shed has a lot of air flow.

If you choose to burn the moldy firewood, do not store it inside your home and place it directly inside your heating device. The real problem with mold happens when people store it inside before using it. This allows the mold spores to potentially become airborne inside your home.

Since you take the firewood from outside and place it directly inside your wood burning device, the mold never has a chance to invade your home. Any mold on the firewood is burnt and goes directly up the chimney and outside.

As an extra precaution, I would wash my hands after handling the moldy firewood.

Overall, I wouldn't worry about the mold you have on your firewood, especially if it doesn't get any worse than what's in your pictures.

Although there is no real "amount of mold" on firewood that renders it useless, mold on the ends is not a big concern. If it was completely covered with mold (the entire log) I personally wold not burn it but I don't think you will have that problem.

Hope this helps,


Comments for How much mold on firewood is too much to burn?

Average Rating starstarstarstarstar

Click here to add your own comments

May 31, 2022
Thanks that was helpful.
by: Anonymous

Thanks that was helpful.

Jan 29, 2014
by: Jonathan

Hello Nick,

I want to thank you for your very helpful response to my post, and to apologize for the long delay in replying.

We are currently moving all of our wood out of the shed and onto the south side of the house, because we discovered that the mold was rapidly getting worse, probably due to the warm, wet winter we have been having until it finally got cold here just in the last week.

At the rate it was going, it might have covered entire logs by the spring, so we sprayed them with some mold killer and we hope that this (along with moving it outside), will take care of the problem.

Anyway thanks again for the helpful advice, and I'm sure we will be regular visitors to your site in the future.


Click here to add your own comments

Return to Ask A Question.