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Does Firewood Go Bad: What To Know Before You Burn

Count yourself among the lucky if you have so much wood that you have to ask if it ever goes bad.  It seems like I am always on the hunt for new sources of wood.  Maybe I just burn too much.  When you find yourself with a cord or two of extra firewood at the end of every winter, it won’t take long to accumulate a lot.  

In fact, you may have firewood that is several years old or even older.  Or maybe you have a neglected stack of wood behind the shed that has seen better days and you want to know if it can be salvaged.  Either way, it’s a fair question to ask.  Does firewood ever go bad?

Assuming your firewood is stored off the ground and protected from moisture, it will take many years for it to go bad.  However, depending on the type of wood, all firewood degrades in quality and produce less usable heat after 10+ years of storage.  Regardless of how it’s stored mold, sunlight and insects will eventually cause firewood to decay. 

However, there is more to it than that.  An inquisitive person like you probably wants to have all the facts needed to recognize bad firewood and how to make it last longer.  Keep reading and together we’ll find the answers.

Can firewood be too old to burn

Not all firewood is suitable to burn but age alone has little to do with it.  Dry, 30 year old wood will certainly burn just like dry firewood seasoned for only 2 years.  You start running into problems if old wood is also rotting or decaying due to moisture.

Firewood is never too old to burn assuming it is dry and still solid throughout.  However, firewood that’s been laying around for 10 or more years away from moisture is probably extremely dry.  It will therefore burn hot and fast which leads to heat loss up the chimney.  Firewood heats most efficiently with a moisture content between 15-20%. 

Even so, I would not hesitate to burn it.  I know people who have heated their homes using old barn wood that has been around for over 50 years.  It was still dry and solid so it burned quite well.  Don’t expect a long burn time from overly seasoned wood though.  Really dry, older wood is best saved for shorter burns during warmer fall or spring months.

If your old firewood falls apart at the slightest touch or feels soft and spongy, it’s not good for burning.  At this point, it is beyond salvaging and needs to be tossed.  Bugs and moisture are likely to blame. 

How long can firewood be stored outside

Most of us stack all our long-term firewood outside where it’s exposed to the elements.  Everything from rain, bugs and sunlight have the power to hasten the deterioration of wood.  And that means wood has a shelf life when stored outside.  But how long can you actually store firewood outside before it is useless to burn?

First off, all firewood you intend to burn needs to be stored off the ground and protected from moisture.  At least if you want it to last.  

With your firewood stored protected from moisture and off the ground outside, it will last at least 5-10 years before it starts degrading in quality.  While it won’t necessarily ever rot or mold, sunlight eventually breaks down the cellulose fibers in wood and bugs may invade your wood stack.

If you can manage to keep your firewood dry, shaded from sun and free of all insects, then it could easily last for well over 10 years outside.  More than likely you’ll burn it before it ever gets that old.

How can you tell if firewood is bad

Now that you know how long firewood lasts under optimal conditions, you might be wondering how to tell if your firewood is past its prime for burning.  Luckily, identifying sub-par firewood is not difficult.  

Generally, bad firewood is either rotten, moldy or punky.  You can tell if your firewood has any of these conditions by how it looks and feels.  Rotten or moldy wood is often damp so it will be spongy feeling and relatively heavy.  In extreme cases, rotten wood breaks apart very easily and the bark separates readily from the wood.  

When rotten or moldy wood is dry, it has a light hollow feel like cork.  Bad firewood can also be punky on the inside which is caused by a fungal infection in the wood.  It will crumble easily just by using your hands.  

Sometimes your firewood might look decent but is actually no good inside the core.  You won’t be able to tell by looking at the outside.  Instead, if you suspect a batch of firewood is bad, take two pieces and knock them together.  Good firewood that is well seasoned and ready to burn makes a sharp rap when banged together.  Bad wood makes a dull thud.

Is it ok to burn rotten or moldy wood

At some point, everyone who burns wood for heat will come across a bad stack of wood.  Maybe you just have a small rack of moldy or rotten wood.  You might be tempted to burn it up to get rid of it but I would hold off if I were you.   

Burning rotten or moldy wood does not pose an immediate problem but in the long run it can lead to smoke damage and creosote build-up.  Rotten or moldy wood, especially when damp, does not burn completely so it smokes heavily.  

Every time you open the woodstove door you’ll likely get a big plume of smoke rolling out the front.  This lower temperature burn, with the added moisture, also adds a fair bit of creosote to your chimney or stove pipe.  All that creosote needs to be cleaned out regularly to prevent chimney fires.  

Overall, burning bad wood is not smart.  Sure, a bad log here and there is not the end of the world.  Just burn clean, dry firewood and you’ll be better off.

Old firewood that is bad isn’t the only thing you shouldn’t burn.  Find out what other types of wood should never be burned in this popular article.

How to make firewood last for years

Fortunately, keeping your firewood in tip top shape for heating your home is simple.  After all, it takes some serious neglect for a stack of firewood to go completely bad.  And why let that happen when you put so much time and energy into cutting and stacking it?  With just a few basic steps you can ensure your firewood will last nearly forever.

Step 1: 

Stack your firewood off the ground.  Always use something to separate the wood from direct contact with the ground.  Among the most likely reasons for firewood going bad is insect infestations.  If bugs like termites or carpenter ants can gain easy access to your wood, they will do a ton of damage.  Contact with the ground also keeps that bottom row of wood wet.

Use 2×4 lumber, paving stones, pallets or even a metal firewood rack to stack your wood on.  It will last much longer and you’ll have fewer pest entering your home too.  

Want to know the best way for stacking firewood?  Take a look at my complete guide to stacking fire wood! 

Step 2:

Cover firewood to keep it dry.  Once you have your firewood stacked neatly off the ground, you need to protect it from rain.  Even if your wood is already seasoned, you still need to keep it covered.  Otherwise, you allow it to reabsorb moisture to a level above the recommended 20% that’s ideal for burning.

I can’t tell you how many piles of wood I see laying around uncovered.  All that effort of gathering the wood is wasted and within a short time it will begin to rot.  Just put a cover over it.  It doesn’t need to be fancy either.  A piece of visqueen sheeting or a tarp is fine.  For those who prefer a more aesthetically pleasing wood cover, build a basic wood shed or lean-to cover.  

Remember, you don’t want to cover the whole stack all the way to the ground.  There needs to be enough air circulation to let any moisture that does accumulate escape.

Step 3:

Organize your firewood stacks and burn on a rotation.  So far, ensuring your firewood lasts as long as possible without going bad is not complicated.  The final step involves rotating your supply of firewood.  If you have more than a few cords of wood, keeping track of which stack is seasoned versus which stack is fresh cut and green might get tricky.  

Try to organize your wood to make sure you don’t ignore one of the piles for several years.  It’s best to burn wood within 1 to 2 years after seasoning is complete.  This way you get the most amount of heat from it during its prime.  Having an organized system allows for easy wood rotation and usage.

Definitely avoid mixing green wood with seasoned wood and never stack wood somewhere you are going to forget about it. 

Parting words

In the end, most firewood that is dry will burn.  Only wet and rotten wood will ever go bad.  Learn to stack your wood properly and you won’t have a problem.  If you do find yourself stuck with a bad batch of firewood, please don’t burn it in your home.  Either throw it out or use it up in the outdoor fire pit. 

Not sure if your firewood is fully seasoned?  Check out my must-read guide on how to tell if your firewood is ready to burn before you go!