There's average data published for various woods -- the heat content isn't the same for all. For the difference between solid wood and sawdust, the difference has to be specie and, perhaps, combustion process. It's also a possibility one or both numbers is wrong or at least inconsistent in what is/was measured.
I've not taken the time to go look much myself as whatever wood there is here is what I can salvage from trimming the elms around the place and they're lousy for firewood, but since there's no forested areas within
If a pound of wood is a pound of wood and a pound of wood is worth
6400 btu's, then why is a pound of sawdust worth 8500 btu's?
Why has this thread gone down a qualitative path when the question that is at the core of the inquiry would seem to be available to quantitative analysis?
Is there a way to solve the problem - or is everyone full of shit?
considering the use of wood for heat, University of Illinois Extension foresters offer the following information and advice: All species of wood has the same Btu (British Thermal Units) per pound of wood; roughly 8600 Btu per pound @ 15% moisture content. As the moisture content goes up in the firewood, the heating value goes down (less Btu's) because more energy (heat) is needed to drive off the moisture in the wood before it will burn. This is why firewood needs to be seasoned at least 6 to 9 months before it is burned. Freshly cut wood is not very efficient for heating use.
These guys are using 20% moisture for 7,000 Btu
formatting link
to Other Fuels
How does wood compare to other fuels? In most
cases wood will be used as supplemental heating to
your conventional system of natural gas, L.P. gas, or
electricity. Table 4 gives Btu values of common fuels.
Dunno. But I do know this - it takes a bigger piece of pine to make a pound of wood than it does maple, and that pine is going to generate a lot more creosote than that piece of maple unless it's really dry - which makes it even lighter. Net/net - pine (and poplar) suck for firewood in the northeast. I burn some pine but more to get rid of it than for any real heat value.
I'm thinking the small particle size leads to more efficient and complete combustion. Similar to the atomization of fuel in an internal combustion engine.
(re posted for the benefit of the blind and the overworked)
Since you are a wooddorker, you must make sawdust.
"Pressed sawdust firelogs. These are made from tightly compressed 100% pure wood sawdust, without the addition of waxes, chemicals or other additives. Pound for pound, these give even more heat than natural firewood ? 8500 BTU per pound in comparison with 6400 BTU for natural wood. They can be used in fireplaces, woodstoves, inserts, and campfires. All in all, these firelogs give all the heat and more of natural wood, and have the convenience of popular wax firelogs."
I think the key is in the "tightly compressed" area. Wood incorporates air and water and other impurities that don't burn. These logs are more nearly pure combustible material and denser than wood so they should yield more heat per cu. ft.
variation from 15% to 20% MC. These guys are using a higher MC to make their product look better. The process of compressing either dries the sawdust further or the dry it ahead of time. The actual caloric content of the fiber structure is not changed, only the amount of water that adds weight to it is regulated. The pressed logs are probably made with sawdust from KD scrap lumber, not just a fallen tree like most firewood.
Simple, use two different BTU measuring devices. I worked in a lab for many moons. If you're looking for a specific piece of data, we could deliver it.
Without more detailed information the data points on that web page are worthless.
Wood is wood - if it is ground to dust or one log a pound of wood will have the same heating value. There is no chemical difference that is dependent on form factor of the wood. It may burn faster or slower or more completely depending on the form factor which affects how well oxygen can get to the fuel - but that doesn't change the amount of heat there.
Now, that being said different species will have different heating values for a pound of wood - it has to do with the amount of resin in the wood. Go read a bag of softwood pellets and a bag of hardwood pellets. The softwood pellets are usually much higher BTU content. I found an EPA report once that gave most wood fiber as having close to
8000BTU/lb, but resin being 17000BTU/lb. Real logs being of course a mixture of both.
There is also the moisture content of the material being burned. Materials have different caloric content - usually measured in BTU/lb of "dry matter". This assumes 100% material and 0% moisture. If you have say 8500BTU/lb dry matter wood, and it was at 10% moisture then you have only 90% of the weight in dry matter. You also need to subtract out the energy to vaporise that water. It takes about 1050 BTU/lb to evaporate that water. This gives us this 8500 * 0.9 = 7650 BTU for the dry matter 0.1 lbs water * 1050 = 105 BTU for the water evaporation. Combine this and we get 7545 BTU/lb of usable heat for that 10% moisture wood.
Then if you get the moisture content high enough and the stove temperature low enough you may get incomplete combustion which means that some of the burnable material goes up the chimney as smoke. This would further reduce the usable energy.
Now of course there are all kinds of wild claims by various people about how much heat is in their particular material. I haven't ever researched the wood stuff as much as corn and pellets. But I do know that in that area there are some WILD exaggerations by some manufacturers. Many use the Dry Matter number and don't account for the moisture content and others just plain out lie.
All that being said I am with Charlie and like good hardwood for a wood stove. It banks nicely for the size stove I have used. I know that pine has more BTU/lb, but I can't get half as many pounds into the stove and because of it's low density and high resin content it burns so fast that much of the heat goes up the chimney rather than being radiated into the room. Maybe if I had a bigger stove, or a different type of softwood it would work better for me. Then there is storage - pine in the wood pile goes punky really fast while oak can be several years old and still great.
Note the google.CA rather than google.COM domain. I like the old interface better, which is still being used by "nationa" googles. I wonder if you Merkins get redirected to google.com when you type in google.ca.
Just because there is a web site that says that or a book that says it, it isn't necessarily so. Wood is wood, and if it has the same moisture content, the BTU per pound will be the same.
Arguments about compression are pretty useless since compression has no effect except to change the density. Arguments about volatiles/resins are in the same category since volatiles/resins won't make that much difference as they displace cellulose (by weight) which probably has a higher energy content per pound that resin.
While some of the stuff in the cited article is pretty standard fair, some of the stuff is just plain wrong. If one wants to really find out about wood they go to one of the wood or forests institutes or groups not affiliated with any product but just promote wood use or wood products in general.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.