Hardness of wood VS BTU output

[J.Noss]

All the time the firewood quality of our hardwoods comes up, yet only from time to time the subject of the hardness of our hardwoods comes up. Well there is a test called the Janka Hardness Test where a steel ball is pressed into the wood and the amount of force required is measured. The result is called the Janka Hardness of that wood. Here is a list of common North American hardwoods and their Janka Hardness. You may be surprised by some of the values.

The higher the number, the harder the wood. I have seen some stated results that shows Osage Orange is the hardest and some that show that Live Oak is the hardest.

-(This is in common AMERICAN Hardwoods, there are other species FAR harder!!)-

Osage Orange 2760
Live oak 2680
Mesquite 2345
Persimmon 2300
Dogwood 2150
Pignut hickory 2140
Mockernut hickory 1970
Hophornbeam 1860
American hornbeam (Ironwood) 1860
Serviceberry 1800
Black locust 1700
Elm winged 1540
Sugar Maple 1450
White Oak 1360
Rock Elm 1320
Red Oak northern 1290
Walnut black 1010
Maple (Red) 950
Cherry 950
Elm american 830

But what I find interesting is that you often will hear it said that "all wood pound for pound puts out the same heat or BTU"
Well, hardness is directly related to density which is directly related to the particular weight of a dried wood.. so a harder or more dense wood SHOULD put out more heat for its size.. Right?

So to my point: often on BTU charts you'll see great discrepancies from chart to chart as well as contradictions to this "rule" that "all wood pound for pound puts our the same heat" And you'll also notice that a great many BTU ratings don't seem to correlate with the hardnesses shown.. but I do find it's alot easier (and more consistent) to find Janka Hardness Test ratings for woods than it is to find BTU ratings, the ones I've shared above are only a few, there's LOTS available online!

So: should people just stop looking at BTU charts when comparing firewoods and just look to Janka Hardness Test charts?

 

[J.Noss]

I'd like it very much if people could add to this very limited number of hardness ratings I've listed with other woods and their hardness.. I know there's sites that have these hardness listings but I didn't want to link off of the fourm.
And if you think my hardness = heat output thinking is flawed that'd be great to heat why too..

Just out of curiosity and interest here is the Janka Hardness of what is thought the hardest woods in the world (that I could find)


Australian Buloke. - 5060
Snakewood - 3800
pe/Brazilian Walnut - 3684
Brazilian Teak. - 3540
Ebony - 3220

 

[Sloughfoot]

I can't find different BTU ratings for different species of White Oak. Just one rating for all. Fairly new to the area and have been burning Live Oak and Valley Oak. The Live Oak burns very well but the Valley Oak is the worst firewood I've ever had and it's had an extra year to season.

 

[Wilhelm]

(European) Turkey Oak

Janka Hardness 1220 lbf (5340 N)
Modulus of rupture 114,3 MPa
Elastic Modulus 10,81 GPa
Crushing Strength 56,4 MPa
ShrinkageRadial 6,0%
Tangential 10,0%
Volumetric 16,0%
T/R Ratio ~1,7

Nearly impossible to burn with just a year of seasoning cut & split.
Two year seasoning You can burn it but foul Your smoke pipes & chimney.
Tree years PLUS is the magic number, You get exceptional long burns, huge ember piles in the burn chamber, and smoke so hot (and clean) You do not have to worry about Your chimney for a season or more.

Because of the above mentioned behaviour of Turkey Oak nearly no one wants it here in Croatia as everyone makes their firewood in the summer for the coming winter.

I burn nearly exclusively Turkey Oak and won't have it any other way!
I am 2-3 seasons ahead in firewood supply.

 

[Wilhelm]

Cornelian Cherry

Quote:
"The Janka hardness of cornelian cherry wood is 4,390 lbf (19,510 N)."

 

[Sloughfoot]

(European) Turkey Oak

Janka Hardness 1220 lbf (5340 N)
Modulus of rupture 114,3 MPa
Elastic Modulus 10,81 GPa
Crushing Strength 56,4 MPa
ShrinkageRadial 6,0%
Tangential 10,0%
Volumetric 16,0%
T/R Ratio ~1,7

Nearly impossible to burn with just a year of seasoning cut & split.
Two year seasoning You can burn it but foul Your smoke pipes & chimney.
Tree years PLUS is the magic number, You get exceptional long burns, huge ember piles in the burn chamber, and smoke so hot (and clean) You do not have to worry about Your chimney for a season or more.

Because of the above mentioned behaviour of Turkey Oak nearly no one wants it here in Croatia as everyone makes their firewood in the summer for the coming winter.

I burn nearly exclusively Turkey Oak and won't have it any other way!
I am 2-3 seasons ahead in firewood supply.

This valley oak will be seasoned 3 years this winter. Maybe that's what it takes like your turkey oak.

 

[Wilhelm]

This valley oak will be seasoned 3 years this winter. Maybe that's what it takes like your turkey oak.

Turkey Oak turns greyish/black past three years seasoning.
As long as it is brownish it is not seasoned and burns poorly at best.

Maybe Your Valley Oak is sap rich as Turkey Oak and needs that extra year to season!

 

[J.Noss]

Cornelian Cherry

Quote:
"The Janka hardness of cornelian cherry wood is 4,390 lbf (19,510 N)."

Interesting!
On further looking I've found:
-The Scientific name for Cornelian Cherry is (Cornus Mas) and they apparently survive down to zone 4-5 (temps -20f to -30f) and grow 25-30' tall.

I'd never heard of that tree before.. I've planted several Osage Orange trees, they grow pretty darn fast in full sun and good soil, would be cool to find a tree that made Osage Orange look like Soft Maple! However the listing for the hardness of the Cornelian Cherry varies quite widely (more-so than most other woods) on a website dedicated to weapons making the hardness rating I've found for Cornelian Cherry are between 2800-3650lbf
So I guess I'll have to try to find some live plants to order!

Here's a picture of a 3yr old Osage Orange I planted, it's 2.5" across the stump at 6" above soil now and about 7' tall (it had shot up to about 15' this year but got so top-heavy that the roots pulled out of the soil so I trimmed the large branch off) I'd very much like to see a full-grown one in person, Central PA

 

[Wilhelm]

Cornelian Cherry is very slow growing and tends to be more of a bush type plant, although apparently it can grow into a tree.

Its cherry like fruits are edible and considered a delicacy for making marmalade, cakes & pies.

 

[J.Noss]

Cornelian Cherry is very slow growing and tends to be more of a bush type plant, although apparently it can grow into a tree.

Its cherry like fruits are edible and considered a delicacy for making marmalade, cakes & pies.

Yes, on further looking on it I find that it is actually a variety of Dogwood (like the Flowering Dogwood) and the only type of Dogwood that yields an edible fruit.. Typical flowering Dogwood have a very hard wood (2150 lbf) perhaps the Cornelian Cherry (Cornus Mas) variety is harder, like a Sugar Maple is to the Maple family.
Now I want to plant a few! Thanks again for bringing this tree to my attention, I find it very interesting.

 

[legdelimber]

Interesting stuff guys.
Sorry to say that My own burning concerns are much more related to what type of junk mail and its ink or coatings, clay content etc...
Throw in whatever random limbs I grab from the neighbors curbside yard "waste.
Just the basic fire pit on the patio nowdays, given that my current address has no fireplace.