Ash in Wood Stove - Softwood vs. Hardwood

[toddnic]

During the shoulder season when I'm burning primarily softwoods (pine, hemlock, and poplar), I tend to have a lot of ash left in the bottom of the wood stove after the fire goes out. Now, I've switched over to hardwoods (red oak and white oak) for the winter season and have very little ash left in the bottom of the stove after the fire goes out. Does anyone on the forum understand why? I'm sure there has to be some scientific explanation.....

 

[moresnow]

Certainly one of our in house woodologists will chime in soon

 

[toddnic]

Certainly one of our in house woodologists will chime in soon

I'm looking forward to communicating with one of those "woodologists!" It's just weird to me why softwood seems to have more leftover ash whereas the hardwood has almost none. I'm sure there has to be something related to density, burn time, as well as the amount of heat produced..... I guess I'm just curious

 

[Squisher]

I'll be curious to hear people's thoughts on this too. Bearing in mind that some softwoods leave nearly no ash, like d.fir. For me I get the least ash off of d.fir espescially compared to hardwoods like Maple. I don't get a lot of true hardwoods though, Birch, silver maple, Norway maple, and I have a coveted stash of oak and locust that I don't know if I'll ever burn. Lol. Because then I wouldn't have them anymore.

 

[shoot-straight]

some woods are ashier than others. pine, i usally get nothing left. gum- its the worst

 

[Squisher]

Ahhh. The technical answer.

 

[Squisher]

Moisture content and how it's burned must be two big factors in ash production. But I'd be curious about what in the woods makeup makes the greatest difference if all other factors were equal.

 

[Highbeam]

I’ve pushed more than a cord of Doug fir softwood through a he stove this year with less than a half inch of ash accumulated. I would say zero but there is a thin ash bed from fall’s alder fuel.

So my experience is the opposite. Tons of ash from hardwood and no ash from softwood.

 

[yooper08]

Disclaimer: I'm not a woodologist.

Through most of the research (Googling) I've done in the past, ash production seems to be largely dependent on combustion temperatures. The higher the temperature, the more mineral content is consumed.

Knowing that, my guess is that for certain woods, particularly ones that don't coal very well, temperatures drop off quickly at the end of the burn, leaving more ash behind. Those that do coal well, they keep temperatures higher for longer, consuming more mineral content. It could also depend on what the mineral makeup of the particular tree is - what minerals it likes to take up and how it stores/consumes/converts them.

 

[begreen]

I’ve pushed more than a cord of Doug fir softwood through a he stove this year with less than a half inch of ash accumulated. I would say zero but there is a thin ash bed from fall’s alder fuel.

So my experience is the opposite. Tons of ash from hardwood and no ash from softwood.

Some softwoods create more ash than others. Hemlock and spruce for example do. I've read that lodgepole pine is high ash content, but have never burned it. Bark can have a much higher silica content which will fuse into clinkers. We see this a lot with thick-barked doug fir.

Folks might find this testing interesting:
http://www.coford.ie/media/coford/c...rdconnects/Ash content of Irish woodfuel..pdf

"The results show that the ash content of a wood fuel (green or seasoned) is affected by species, assortment, tree size, location and time of harvesting and chipping method."

 

[toddnic]

Folks might find this testing interesting:
http://www.coford.ie/media/coford/content/publications/projectreports/cofordconnects/Ash content of Irish woodfuel..pdf

That article is interesting. It focuses on wood in various forms, not just firewood, but the conclusions are valuable. It is interesting that when I burn hemlock, pine, and poplar, I get a significant amount of ash. Whereas red and white oak produce very little. I wonder what hardwoods Highbeam is burning?

 

[begreen]

Out here good dense hardwoods are not as common. We have lots of soft maple and alder and some madrona and wild cherry. I got lucky and scored some locust a few years back and have burned a bit in the past week. The ash build up is notably greater than with the doug fir I regularly burn. I had about a half cord of doug fir ashes and like Highbeam would probably make it past Christmas before dumping ash. But with the locust I'll be cleaning the stove next weekend.

 

[Highbeam]

That article is interesting. It focuses on wood in various forms, not just firewood, but the conclusions are valuable. It is interesting that when I burn hemlock, pine, and poplar, I get a significant amount of ash. Whereas red and white oak produce very little. I wonder what hardwoods Highbeam is burning?

Hardwoods are deciduous trees. Our local hardwoods are lower btu than what you might find elsewhere. Also isn’t Doug fir a spruce? It’s not a fir that’s for sure.

Our hardwoods are red alder, big leaf maple, poplar, aspen, random junk, some cherry and madrona. Definitely not a lot of oak or hickory!

 

[begreen]

"Douglas-fir is the name of an entire genus of trees that contains six species--two native to North America and four native to eastern Asia. Because of its similarity to other genera, Douglas-fir has given botanists fits. It has, at various times, been called a pine, a spruce, a hemlock, and a true fir. In 1867, because of its distinctive cones, it was given its own genus--Pseudotsuga--which means false hemlock. The hyphen in the common name lets us know that Douglas-fir is not a "true" fir--that it's not a member of the Abiesgenus.

Only one Douglas-fir is native to the Pacific Northwest, and it's by far the most important member of the entire genus. Its common name is identical to that of the genus, reflecting its importance. Douglas-fir (Pseudotsuga menziesii) is Oregon's state tree."
https://oregonstate.edu/trees/conifer_genera/douglas_fir.html

 

[schortie]

Don't burn much softwood here, but black walnut creates the most ash of any other species I burn.