Effect of Wood Hardness on Firewood

[shinyplanter]

To my knowledge, among the physical properties of wood, density is the principal contributor to firewood quality/value, as a given unit of volume of denser wood has greater thermal energy content/btu compared to the same volume of less dense wood. I’m curious what, if any, role the hardness of the wood has on firewood quality/value. For example, if the wood from two species has equal density but one has Janka hardness >10% more than the other, will there be any noticeable difference in the burning characteristics between the two, all else equal. I think a comparison of white oak and black locust is pretty close to a real world instance since black locust is only about 2% denser but 26% harder than white oak. From my experience, I would probably rate black locust as modestly superior to white oak though it does seem to be more stubborn about igniting. It also seems that black locust produces especially hot and long-lasting coals and very fine ash.

 

[begreen]

That's about right. Hedge (osage orange) is like that too. There is another thing that can affect btu content of wood, that is oil or resin content. Doug Fir is a softwood, but has decent BTU content, better than some hardwoods. Another desirable trait is the amount of ash the wood makes after combustion. Doug Fir is great in this regard, making very little ash.

 

[shinyplanter]

If wood hardness has any effect, all else equal, what would be the nature of any effects and what about hardness contributes to those effects. The benefit of greater density is obvious and needs no explanation but if hardness does have effect(s) I’m not clear on the mechanism(s)...

 

[RockyMtnGriz]

Why does this feel like training AI to me?

I calculate value differently. Fuel moisture being equal, the highest value wood is the one that yields the most pounds of wood for the least amount of work.

A dead tree regardless of species, that has fallen across the driveway and is only yards from the woodstove possesses exceptionally valuable wood. Since I'm going to have to cut it up anyway, the additional work to transport it to the stove is minimal.

 

[EbS-P]

Hardness is related to density. Air isn’t hard. But I would imagine the differences in hard mess come down to the cellulose lignin matrix.

Lignin - Wikipedia

en.wikipedia.org

As for firewood. In general to harder woods produce more ash? I would say ash content is more important than hardness but less important than density for a good firewood

 

[Caw]

The ashiest wood I burn is red maple. If I'm burning through a week of it I'll need to clean my stove every other day whereas with red oak I won't need to clean it at all. Fwiw Red maple is known as "soft" maple because it's less dense than sugar maple which is "hard" maple.

I agree with the above post though. Convenience is a major factor. I have mixed hardwood logs delivered to my driveway a couple times a year. The best firewood for me is whatever species he delivers. Thankfully for me I live in a red oak, maple, ash (formerly), and cherry dominated area. The pines are also very prevalent but usually end up in the chipper or at the lumber mill.

 

[Eman85]

Wood hardness to me is how hard is it to get it processed and in the stove.

 

[shinyplanter]

Hardness is related to density. Air isn’t hard. But I would imagine the differences in hard mess come down to the cellulose lignin matrix.

Lignin - Wikipedia

en.wikipedia.org

As for firewood. In general to harder woods produce more ash? I would say ash content is more important than hardness but less important than density for a good firewood

Wood ash - Wikipedia

en.wikipedia.org

It sounds like the primary components of wood ash tend to be calcium carbonate and/or calcium oxide the production of each apparently being temperature dependent. Calcium oxide is ~20% denser than calcium carbonate so it would see that carbonate-heavy ash would be fluffier/more voluminous than oxide-heavy ash. I wonder how the combustion products of lignin compare with those of cellulose...