Drying firewood too long drastically reduces Btu content?

In all my years of burning firewood I’ve never heard this argument.

The guy from Kuuma wood furnaces claims that if you season your firewood too long, you not only reduce the water content, you lose combustible fluids that make up 2/3 of the Btu content in your firewood. According to him, the dry cellulose is only 1/3 the Btu content of the firewood.

Has anyone heard this before?

I’ve seen old firewood become light and punky but assumed that was due to the wood itself rotting.

 

If I recall correctly someone stated that their Kuuma owners manual stated that it performed best at 25% moisture. As opposed to most stoves state 20% or less.

 

So I posted before watching the posted vid, I would think that he was referring to the Birch they had there. I have no experience with birch but it’s a 2-3 process here to get most woods down to around 20%. I believe stoves & the Kuuma furnaces burn a bit differently but again I have no experience with Kuuma furnaces & that’s based on my readings from owners & their experiences.

 

I’d love to hear from someone who has experience with both Kuuma and wood stoves. brenndatomu ?

 

I find it kind of amusing that he first says wood that is too dry has only 1/3 of its heat value left, then in the end he says if your wood is too dry you need to give it less air or else it will over fire and get too hot.

 

Which "combustible fluids" make up 2/3 of the BTU's??

 

Dale (the fellow in the video) n I have hashed this out several times...pretty much went back to our respective corners agreeing to disagree.
Me, and other Kuuma owners have beat this subject to death with personal trials...the bottom line is this (IMO) they (and most stove companies) have to design them to burn some range of MC...so they design for the EPA test, and the masses (which means wetter than optimal wood)...will the Kuuma burn it without a complaint, yes, will it make more heat with dryer wood, yes. The only issue I find with using less than say, 18% MC wood is that if its real cold and you load up a huge load of uber dry wood, it can set the high temp alarm off on the furnace, which is no big deal (just annoying) it doesn't mean the furnace will be harmed, or that there is even a problem necessarily, just that the firebox has gotten up to XXXX temp, and you need to make sure that the firebox/ash drawer doors are properly latched, and that the chimney draft isn't out of spec for some reason. (I run a manometer on mine full time) if everything is OK, then run it! Mine seems to want to set the HT alarm off easier than what some other owners have experienced...one owner has had several over the years and he agrees that he had one that seemed more prone to it than the others. Like I said though, its really not an issue, and dryer wood still seems to make more heat in my (and others) experience. Dale claims they have the opposite experience, less heat due to less burn time, but I think its just the difference in wood available between northern Minnesota, and NE Ohio...we have mostly high BTU hardwoods, and they use a lot of birch (IIRC)
While I disagree with Dale in this video, don't let that skew your view on the company...the Kuuma wood furnace is no joke, its the real deal...there is not a finer wood fired forced air furnace available...and Lamppa is on the same level customer service as Woodstock (for those that have dealt with them) There are quite a few Kuuma owners here...have to shake the rust off n see if I can remember...me, JRHAWK9 , @commanche79p, Sluggo, Matthewchopswood , yooperdave , zymguy , woodey ...there are a bunch more owners here, I'll just have to dig around in the ole memory banks a lil more...
Any further input JRHAWK9 ?

 

Maybe these newer burning appliances require a higher MC, but I'll take my chances burning stuff under 20% MC.

 

I asked about where that came from...he referenced Daryl (the owner and co-inventor, who really is a wood burning expert...more like savant...hard to argue with their results, and success!) who said it's in this book, which I own, but do not gather the same conclusion from as him...maybe my reading comprehension is just poor.
The Wood Burners Encyclopedia, Wood As Energy, by Jay Shelton, CR 1976

 

Almost nobody else is willing to post their test results...
Lamppa Kuuma Vapor-Fire Testing Reports for EPA Certification

EPA now wants Lamppa furnaces to help fix testing woes - The Timberjay

 

The moisture in hardwood is simply sugars (from photosynthesis) and minerals from the soil. Sugars do burn. So if the water evaporates the sugars should be left behind with the cellulose. That’s why his claims didn’t make sense to me.

The sap in conifers is a different story altogether. It is volatile. But I don’t think even the types of softwood available to him contains much if any sap.

 

I was waiting for him to say what the combustible fluid were, but he never did. I don't know if I have ever seen firewood under 10% mc.

 

Heck, kiln dried lumber doesn't even stay that low in most places!

 

I had some Osage that was in the single digits & probably have more that is testing in the single digits but Osage is a rare firewood for most & has different characteristics than most other woods also.

 

I have some Osage orange, hedge, that's been drying for over 20 years. It's dry, it has waxy dried sap in it. It will burn hotter than anything else I've put in my stove. It's only for the coldest of winter days and nights. Still used only mixed with ash, oak, or hickory.

Water consumes huge amounts of heat to boil off and then the vapor can suck up more btus. The only volatile fluids I can think of is wood gas. Those typically are burned off in a hot fire.

 

Yep. Water can absorb massive amounts of energy. Once it turns to steam, it can absorb even more. And all that energy gets carried up the stack.

A rough figure is 1,000 btu for every lb of water to turn to steam. If you put 40 lbs of wood in a stove and it is 20% water, that's roughly 8,000 btu just to make steam. That means it took a lb of wood just to boil that water.

 

You would have to catch it at just the right time of the year, but even if then, according to the equilibrium moisture chart poster in resources here, 12.7% is about as dry as you would expect to ever see in your area...it's about the same here...14-15% is more common.
Equilibrium Moisture Content of wood in outdoor locations

 

Maybe he means sap like found in pine or other conifers? Creosote bush?