On Fri, 28 Nov 2003 18:32:14 -0000, "Nick" wrote:

Hardwoods to avoid for poor burning (mostly simply high moisture
content) poplar, willow, elm, holm oak and turkey oak.



One of the best woods we have ever burnt was ELM !!
This was dry though, but burnt long and hot with little ash.

Yes, since the 70s a lot of elm has been available as dead standing
wood, also the beetle forms galleries under the bark which bird
subsequently knock off in their searches, so the pole desiccates
standing. Green elm has a 140% water content dwb (IIRC).

Are these to be avoided woods bad only when wet ?

Yes. You can make a fairly good estimate of the heating value of wood
by first subtracting the ash weight then multiplying the remaining dry
wood weight by 18MJ and subtracting the water weight times 2.7MJ (this
makes fairly broad assumptions about flue temperature).

To refine this a bit you need to treat the proportions of lignin,
cellulose and hemicellulose separately, lignin has the highest
calorific value and forms a larger portion of conifer wood.

and which are the good ones then when wet / recently cut and logged ?

Ash by a long margin then probably birch and sycamore.

AJH