BTUs....stove temp....and the heat you feel

[ChadMc]

Scored 2 big oaks from a neighbor the other day and have it set to season for 2+ years. I’m pretty new to oak. Mostly what I burn is ash, cherry, and black walnut. So here’s my odd question haha......if I can easily reach optimal stove temp with a load of ash and have the stove cruise at 500-600 for hours with secondaries what about oak is going to burn hotter? I know it burns longer and coals better but if I don’t want to go above that safe sweet spot temp on the stove how is it actually burning hotter or rather heating the house warmer. Is it putting off a different feel or radiant heat?? I’ve has loads of basswood and couldn’t get the stove above 400 so I see the difference there but if cherry or ash takes my stove to it’s sweet spot then what’s different with the magical oak? Ha this could be a dumb question but had me thinking as I’m Processing all this oak.

 

[Highbeam]

All loads have a cycle. Ignition, off gas flame heat, then coaling. With higher btu wood and a controllable stove you can stretch out the length of time that the stove stays at the desired temperature before dropping into that cooler coal stage.

 

[kennyp2339]

All hardwoods have the same btu release per pound, about 8,600 btu's.
So you have 1 oak split at 10lbs, but 2 splits of cherry of the same size to equal 10lbs. The potential btu calculator of different wood species is made using a standard measurement, in our case its 1 cord (4ftx4ftx8ft) So oak might have 100,000 btu's out of a cord since its more dense, and cherry might be 75,000 btu's out of a cord since its less dense and will take more pieces outside the cord foot print to hit the 100,000 mark. Please don't take 75,000 or 100,000 number as truth of species, I just used those numbers for better explanation.

 

[ChadMc]

All hardwoods have the same btu release per pound, about 8,600 btu's.
So you have 1 oak split at 10lbs, but 2 splits of cherry of the same size to equal 10lbs. The potential btu calculator of different wood species is made using a standard measurement, in our case its 1 cord (4ftx4ftx8ft) So oak might have 100,000 btu's out of a cord since its more dense, and cherry might be 75,000 btu's out of a cord since its less dense and will take more pieces outside the cord foot print to hit the 100,000 mark. Please don't take 75,000 or 100,000 number as truth of species, I just used those numbers for better explanation.

Makes sense. I guess I’ve wondered I can heat the house so well with my hardwoods I’m using now what difference is this oak going to do haha, get the house to 90deg.

 

[fvhowler]

Just burn and learn. Wood species is one of the many variables running a wood stove and heating your house.

 

[Ashful]

I burn a ton of oak. Actually, now that I think about it, more like 20 tons of it per year. I also get a few tons per year of other miscellaenous stuff, mostly ash, but also some hickory, walnut, sassafras, maple, whatever.

The biggest difference I notice is burn time. At the same thermostat setting on my BK, the oak runs longer than most other woods. Of course, I said "thermostat" and not "air control", the BK is going to adjust the inlet air to try to keep the same temperature for a given thermostat setting, no matter what you load into it.

So I'm watching this one with interest. I really don't know what to expect in a non-thermostatic stove, in a house that doesn't have an infinite capacity to soak up heat, but I already suspect Kenny's answer is closest to right.

 

[peakbagger]

Btus produced is heavily related to density and lignin content. The pellet making process effectively equalizes the density of the contents of the wood by drying and compressing the wood, then it comes down to lignin content. Lignin burns at a higher temperature than cellulose and softwoods have a higher lignin to cellulose ratio. The general consensus is softwood pellets have a higher Btu content than hardwood pellets. This is counter intuitive as the average persons experience is that hardwood logs burn hotter than softwood. When burning logs the density is far more important than the lignin content. Softwood grows faster and how it does it is by incorporating thinner cell walls and large internal voids while hardwood have thicker walls with smaller voids. Slice a piece of softwood and hardwood, look at them with a microscope and its real obvious. So if you have woods of equal density at the same moisture content they are going to have a roughly the same btu content if they have the same lignin content. In the case of pellets the density is taken out of the picture so the softwood wins out on lignin content.

This technical article goes into a lot of detail on lignin content https://www.google.com/url?sa=t&rct...white87a.pdf&usg=AOvVaw38sHCDln5UvEP34g0y23Ek

Lignin is a byproduct of the pulping process for paper, when the water is boiled out of it it looks like roofing tar and burns as hot. The big next step for burning wood that hasnt happened widely on the commercial scale is pyrolysis and torrefaction of the wood which breaks down the low btu cellulose and converts it into a higher carbon residue mixed with lignin. The resulting product is sometimes called "green coal" It burns hotter and longer than pellets or chunk wood and its density is quite high somewhere between coal and wood. Unfortunately the cost to make it drives the price higher than the market will bear.

 

[ChadMc]

when your firebox is brought to operating temp do you feel the same heat regardless of what species or BTU type your have it loaded with. A higher BTU will seem to stay at that perfect burn and temp longer. Kind of an odd question haha. Oak is so desirable because of its long burns? I just scored a lot of oak and I’m just nerding out at this point.

 

[Ashful]

To me, oak is desirable because I don’t have enough free hours of good daylight weather to fell, skid, haul, buck, split, stack and load all the wood I need. So, I might as well spend the limited time I have on the highest BTU wood easily available in our ‘hood, to get the most out of those hours.

 

[Highbeam]

And let’s not forget that some hardwoods are very low density like cottonwood, poplar, basswood. Far less dense than the denser softwoods.

 

[Ctwoodtick]

I’ve always thought and felt that the temperature you feel is the same with any of the woods you would burn. I believe that it’s only the length of burn time that would be impacted. I think that you would be affecting stove top temperature a lot more with factors such as size of your Splitwood and amount of air space thatYou allow in the firebox (Example would be if you stacked crisscross style and firebox you’re going to get a hotter burning fire and then if you did if you had larger splits of wood laying on one another with minimal gaps in between). The other main factor of course would be how dry the wood is that you’re using. This can make a very surprising difference even if the difference is as low as a couple of percent moisture content. You will see a huge difference between a piece of wood that is 23% versus 17% for example.

 

[Highbeam]

If not for the window you wouldn’t know what wood is inside a 600 degree stove. It’s just hot. The trick is that it can’t stay at 600 as long with cottonwood as it can with oak. It’s time at 600 that makes the house hot.