Drying firewood too long drastically reduces Btu content?

I had also wondered if firewood can be too dry for optimum heating.

I will have to find the book and reread on this topic, but in “Norwegian Wood” by Lars Mytting I recall that he referenced studies by Norway’s Firewood Ministry which found that hardwoods, stored properly well over 30 years are still considered prime firewood for most heating applications.

 

Maybe he’s burning old Jack Daniels oak barrels?

 

Here is reviving an old thread. Saw a YouTube video where this guy says firewood loses heat value if stored too long. I googled it and low and behold this thread popped up at the top.
Asked my physics major son what he thought and he researched it and found from Purdue Forestry and Natural Resources research paper, 10 year old seasoned wood does have less Btu value than 3 year old seasoned due to volatile compounds evaporating and micro breakdown of cell structure.
So I have several cords of 9 year old oak firewood in a shed that I call my IRA firewood, not to be burnt till I absolutely have to use it. I'm rethinking not burning it (besides I'm of the age that have to do minimum distribution anyway) and might burn some this coming winter as I am 3 years ahead in my regular rotation stacks. I found a piece I weighed originally in 2017 and after 3 years the weight stabilized, but I just weighed it and it has lost .5 pound since the last time I weighed it in 2023........so it is probably worthless and I should just take it back in the woods and dump it. Ya.....right.

 

LOL!!!

Ask Eric Wanderweg what he thinks of burning ten year old mulberry!

Possibly true for lower BTU species, but like you, ill take my chances with 10 yr. old wood dried in a shed/barn.

 

I'm almost surprised that you remembered about that mulberry score from almost 4 years ago now. Thanks again for finding that score for me
The fruits of my labor was this Labor Day fruit wood
Yeah, the ten year old limb wood was dry all the way through, so I CSS'd it and burned it that very winter. It burst into flames violently and output a ton of heat for a good long time before turning to ash. There was no loss of BTU's there whatsoever.
IME I've burned some very old past-prime oak in the past that had lost some of it's potential burn time, but I don't equate burn time with BTU output. I've burned loads of low BTU pine and cherry that left me good coals after 16 hours.

 

A wood hoarder NEVER forgets a good score!

P!sses Ms. buZZsaw off how I can remember stuff like that and forget what she said five minutes ago.

 

Interestingly, the research paper indicated exactly what you observed, that it would ignight quickly, burn hot and leave a lot of ash.

 

I think we can all agree that over dried firewood is not a problem that many face in the burnin wood business. It's going to be the opposite 99.9 percent of the time.

 

Aint that the truth!

Ive had people complain about my wood being too dry! "My wood is not too dry, your wood is too wet" is my reply.

Most burners are so used to burning (or trying to burn) wet/underseasoned wood they think it to be true.

 

Agreed. They shop for the lowest price and get the sellers who cut, split, and sell, all in one day.

 

Copied this to like it twice!

 

I quickly searched for that paper, but did not come up with it...but did get this from AI.




Firewood That’s Too Dry — What It Means and How to Handle It
Firewood can indeed be too dry, even though the general rule is to dry it before burning. The problem isn’t that dry wood is unsafe — it’s that extremely dry wood burns too quickly and hot, which can make it inefficient for home heating Chainsawnerds+1.

Why Dry Firewood Burns Poorly

• Rapid combustion: Wood under about 10% moisture content ignites instantly and burns with a short, intense flame Fireplace Tips.
  
  
• High airflow needs: The fire reaches its combustion temperature quickly, so it demands more oxygen, which can draw heat up the chimney instead of radiating it into your space Chainsawnerds.
  
  
• Reduced heat output: While the initial heat is strong, the overall sustained heat is lower than with properly seasoned wood Chainsawnerds.
  
  
• Frequent feeding: You’ll need to add more logs often to keep the fire going Chainsawnerds.

Ideal Moisture Content

• Best range: 15%–20% moisture for optimal burning — clean, hot, and long-lasting Chainsawnerds+1.
  
  
• Too dry: Below 10% — burns too fast and hot.
  
  
• Too green: Above 20% — hard to light, produces more smoke and creosote Fireplace Tips.

Signs Your Firewood Is Too Dry

• Burns instantly without much effort.
  
  
• Requires constant feeding.
  
  
• Produces a very hot, short-lived flame.
  
  
• You can feel intense heat radiating up the chimney.

How to Use or Adjust for Dry Firewood

• Adjust fire-building: Add larger logs to slow the burn, or mix in some slightly green wood to balance moisture Chainsawnerds.
  
  
• Reduce airflow: Close the damper slightly to lower the flame temperature Fireplace Tips.
  
  
• Soak (optional): For very dry wood, soaking it briefly can slow the burn, though it adds extra fuel to boil off the water Fireplace Tips.
  
  
• Use as kindling: Extremely dry wood is excellent for starting fires but not ideal for long-term heat.

Seasoning Tips

• Split logs to increase surface area for drying.
  
  
• Store off the ground, in a dry, well-ventilated area.
  
  
• Allow 6–12 months for best results, or use kiln drying for faster results Fireplace Tips.

Bottom line: Firewood can be too dry if it’s under 10% moisture, but it’s still safe to burn — just manage the fire differently. For steady, efficient heat, aim for 15–20% moisture content

 

I call BS and not against you brenndatomu
Vermont which has one of the highest % of wood burning for heat in the country, requires to receive cord wood under the LYE heat program federal government guidelines for heat assistance for low income. The firewood must be kiln dried which provides those to dry conditions.

Vermont used to be a run by farmers with common sense. Has done numerous studies on insulation and heating. That is why they put in this requirement probably 25+ years ago.

Because others believe it the AI states fireplaces in the cold of the north the differential between inside and outside without a damper to slow chimney; actually has been proven to let more heat out in a burn cycle than it produces inside the home.

obviously this would be different in different climates.

 

Who made chainsaw nerds the authority on firewood? I bet they don’t even use chainsaws.

 

I much rather have to evaporate one half of a percent less water in my stove at the cost of some volatiles lost, than the reverse.

 

Virtual saws...at the highest level of expertise...

 

Splitting hairs...anything between say 10 and 20% MC will work

 

Very dry wood has the same stored energy as not so dry wood, it just releases it much faster, depending on setup that could mean much of that goes up up and away before it has a chance to do its job. Maybe that's where the less BTU comes from?. You of course lose a little less btu to offgassing moisture, but the difference from lets say 18% to "very dry" is really negligible.

Disclaimer I only read this page

 

My thoughts exactly. Mebbe they can give us a sharpening tutorial while they're at it!

 

I agree it's splitting hairs, and I agree it'll work - as in burn cleanly.
But if one talks about what's worse, my view is that losing some volatiles (that burn off quickly anyway, so provide only a small percentage of the energy released in a 8 hr burn or so) is preferable over having to spend that and likely more energy on dealing with the water.

The more important point is, I think, that after 4-5 years, one does not loose any more water because the equilibrium moisture content is reached.
So at that point one may loose a little bit of volatile energy, but I think that the firebox packing density, wood variation, etc. will be more variable than the minor energy loss - so it's unlikely one actually notices the energy loss due to having 10 year old wood.