A few months back I signed up for the Garn newsletter because I like to build my knowledge base and to me Garn has it figured out. So, the most recent newsletter had a video and the video right after was this one: Plain and simple what we all know on this site. To me if someone is a beginner at burning this is what they should watch first. Its all about BTU's I just found it interesting. Maybe it has been posted and I missed it.
It was new to me - good info there! Thanks for sharing! Why do these things always have a 'takeaway' about burning wood that's 'too dry' though? That's just a pet peeve of mine... Is that actually a real-world problem? Has anyone here ever had a problem with wood being 'too dry'? Needed to set it out in the rain for a little bit, so it burns better?
Are we talking martinis or wood? Is this where theory meets reality...and reality slaps you in the face? Cool video though...learning is gooder.
I remember my boiler came with a chart that suggested wood with 40% moisture content has 60% of the energy output as wood at 20% moisture.
I tested a 2x4 that had been in the barn for a few years, off the ground of course-14% MC. That has to be moisture equilibrium here, and not too dry.
Yeah, I too thought, "too dry" I don't think you can get it to 0%. Fox, I agree that a pc. of wood laying on the ground inside at 14% is equilibrium. But, I think the point in the exercise is to explain to beginners how moisture effects the Btu's.
I've burned scraps out of my wood shop for years, and the equilibrium MC is usually around 9-12% depending on the season. The shop has a floor slab which contains radiant heat tubing so the wood tends to be drier than if stored in a garage or shed. Those scraps burn very cleanly and efficiently and I would never say that they are too dry. The video was certainly a very plain and clear explanation. Well done, GARN.
Reality: It takes a little over 1000 BTU to convert 1 pound of water to steam at atmospheric pressure. If I have wood at 21% moisture using his equations I am changing 0.18 pounds of water to steam for every pound that I burn. Do the math. I use some of that 7200 BTU/pound wood to boil off 0.18 pounds of water. (1000 x 0.18)/7200 I burn over 180 BTUs to evaporate the water so my 7200 BTU/pound is now only giving me 7020 BTU/pound that I can then put into my 80% efficient equation for the stove. 0.8 x 7020 = 5616 BTU real heat available for a pound of 20% wood in a very high efficiency stove. Note, the reduction from 8800 BTU/pound to 7200 BTU/pound does not take boiling into account. It merely subtracts out the total from the weight because now only about 80% of that weight represents wood fiber, the rest is water. The energy required to boil off the water gets added to the total loss.
Decent video and has the right ideas. I just do not like their figures of 20-30% moisture. Much better to be <20%. And as others have stated, I too have never seen wood that is too dry. Once again I'll bring up some wood where we we had several MM that were involved in testing with the lowest in at 8%. I think the final tally was they figured around 9%. So, the real question is, how did it burn? Fantastic!
I would be willing to bet when the founder of Garn if pressed he would admit that less than 20% would be preferred. But, in reality can they get people to dry would that well? So, I think they design the boiler to operate at the 20%-30% range so they will sell boilers. I wish I were younger and had the real estate to put in a Garn because I think they are fantastic boilers - not that there aren't others to their equal as well. But, for now the zero-clearance supplemental is going to keep me addicted. Shoot, its almost 4;30 time for a cool one. Great discussion.
