Seasoned vs Unseasoned Length of Burn Time

[jkbemdavis]

So I have been reading with great interest many of the posts about the benefits of burning properly seasoned firewood vs. unseasoned firewood. (ie: more heat produced [btu's], less smoke/creosote, etc.) What I haven't yet determined is if there is a clear answer on length of burn time... particularly in an outdoor wood boiler setup. I have a neighbor who has been heating with an OWB for approximately 15 years. He swears that in his experience he has gotten longer burn times by using unseasoned firewood, and even went so far as to say that he will even put in wood that is so freshly cut down that there are leaves still on it at times.

I'm interested in all of your thoughts. I'm fortunate enough to have an abundance of firewood available, and a barn with room for storage and air drying, so for me this is more of an academic issue... I want to learn the very best ways to heat.

For the record... I have heated with wood myself for 10+ years as well, but have not properly seasoned the wood as that was in another house with a different arrangement, and I never was able to be more than 6 months ahead of the firewood.

Thanks for sharing your thoughts.

 

[DougA]

So I have been reading with great interest many of the posts about the benefits of burning properly seasoned firewood vs. unseasoned firewood. (ie: more heat produced [btu's], less smoke/creosote, etc.) He swears that in his experience he has gotten longer burn times by using unseasoned firewood, and even went so far as to say that he will even put in wood that is so freshly cut down that there are leaves still on it at times.

I don't think you will find anyone here that will argue with that quote. Unseasoned wood will burn longer and many times you will have chunks of charcoal left over that are hard to burn off.
The error you are making is comparing length of burn time with BTU. (heat). Unseasoned wood uses up a lot of it's energy potential (BTU) in burning off all the moisture. There are lots of charts on the internet that will give you green vs. dry BTU values for all the species of wood. The difference is substantial.

In fact, some of us will combine a few less seasoned splits that might be 20-25% moisture with dry wood for a longer overnight burn. 20-25% is actually seasoned wood according to many people who sell hardwood.

Many of us think 18% is a really good sweet spot. Less than that can cause overfiring if you are not careful.

 

[jatoxico]

The way I see it it's hard (actually impossible) to argue with the logic that available heat energy needs to be consumed to boil off the water in green wood. That results in a longer cooler burn. It seems to me that people see this as an advantage when using stoves that they can't control.

Many older stoves seem to fit into that category and would tend to over-fire with wood dried to an EPA stove standard. IMO they were really designed to use wood many here would consider partially seasoned. With a a bad setup and/or practices they can be creosote factories. With a good setup they can run w/o clogging up the stack. Problem is either way they put out a lot more particulates and use more wood.

 

[Firefighter938]

I don't have an owb, but have several friends who do. They like a mix of dry and green wood.

I think some of the difference is that with an owb you have forced air fans to assist burning the green wood. The dry wood burns up without the need of the forced air because it doesn't have water slowing it down. So you put a load of dry wood in, the thermostat calls for more heat and it burns, then the fan shuts down and it continues to burn hot even though that heat isn't needed.

The green wood burns when air is being forced on it, but then slows down considerably when the fan shuts off. The furnace calls for more heat and the forced air fan kicks on and the fire intensifies again.

The dry wood burns hotter and produces more btus, but the btus are wasted because the furnace isn't calling for heat. A stove inside a house dumps a lot of that heat inside, and raises temp no matter what.

I hope that makes sense. I am typing on my phone. I don't really know if this is true, just my thoughts.

 

[Poindexter]

I recently read a diary, hang on, hasn't gone back to the library yet. _Diary of and Early American Boy, Noah Blake, 1805_ by Eric Sloane. c. 1965 Wilfred Funk Inc, reprint Ballatine 1974.

The kid, Noah, turned 15 in 1805 and kept a diary of what he was doing. He was working hard all day every day all year, but didn't put up his family's firewood for the winter of 1805-06 until November 1805. I raised an eyebrow when I read it, but the family house had an open stone fireplace for both primary heat source and primary cooking.

Many of us are(were) father -son -grandson recipients of the same modus operandi, but it just doesn't work correctly to feed modern stoves fuel that damp.

I frequently ask (rhetorically) if folks would choose to run their new 2016 Corvette on 85 octane gas.

 

[ElmBurner]

Yeah, makes sense to me. Boiling off water keeps the temps down, cooler wood burns slower.

The difference is the BTU you get out of it. The fire is not as hot, in other words.

I think OWBs are sort of an odd duck, because of how they operate. If you add more mass to the system, then it starts to make sense to burn dry wood. But when you are doing short cycles with forced air input, then green wood starts to look better (but your neighbors will hate the smoke! ).

 

[jkbemdavis]

Thanks all for your thoughts. Thanks to a generous winter season and a generous schedule that has allowed me time to get ahead somewhat I should have some nicely seasoned wood ready for next year, and am working beyond that also. I'll probably store up as much as possible, and not worry about mixing in anything that's more freshly cut as well.

 

[St. Coemgen]

Unseasoned wood will also create more particulate matter (i.e. soot, et al.). Burning unseasoned wood only makes one a poster child for the anti-wood burning crowd who are quick to point out the emissions from burning unseasoned wood. So, the simple solution is: only burn seasoned wood. It is ideal for you and everyone else.

And also tell everyone else giving you this lousy advice to also only burn seasoned wood.

There does seem to be a some "long burn" mania that puts ridiculous notions forward in an attempt to achieve the singular "long term burn" agenda despite all other factors; and that really misses the point.

There are products and stoves designed for clean, long burns. Simply use those.

 

[peakbagger]

A former girlfriend was divorced after a long marriage to diary farmer. The heated with wood that was normally cut in the fall so it was green. I convinced her to get a couple of cords the year before and we cut and split it and let it sit for a year. She was sure she didn't have enough wood but discovered it took a lot less dry wood to heat a house then wet wood.

Unfortunately for most stoves a clean long burn is myth. Cats and secondaries help but the right way to burn wood is full out as hot as you can get it and then store the heat you generate in a storage tank. Dick Hill proved it 35 years ago and things really haven't changed.

 

[FTG-05]

A former girlfriend was divorced after a long marriage to diary farmer. The heated with wood that was normally cut in the fall so it was green. I convinced her to get a couple of cords the year before and we cut and split it and let it sit for a year. She was sure she didn't have enough wood but discovered it took a lot less dry wood to heat a house then wet wood.

Unfortunately for most stoves a clean long burn is myth. Cats and secondaries help but the right way to burn wood is full out as hot as you can get it and then store the heat you generate in a storage tank. Dick Hill proved it 35 years ago and things really haven't changed.

Who is Dick Hill and how did he prove your previous statement?

Personally, I've never understood the obsession of some people for turning the air down all the way and smoldering their fire so "it lasts all night". Of course, I don't live in the Siberian/frigid north so have a limited experience with it. But my priority has always been safety first, heat second. It just doesn't make sense to me to have "all night burns" when you're crapping up your chimney with creosote, and therefore risking your home, life and the lives of your family.

Finally, and my real point: is that I totally agree with the get the fire hot and store the heat remark above. And it's reflected both in how I designed my wood stove/chimney system and how I run my 30-NC. I get the fire and stove hot and don't turn down the air until at least an hour or so, then let the heat get stored in the +450 lb wood stove and perhaps +1500 lbs of stone work and concrete board. Even if the fire went out several hours before we go to bed (we like it a little colder at night), when I get up in the morning, I can still feel the heat coming off the wood stove and stone work alcove.

 

[peakbagger]

Here is an old article, unfortunately his wood boiler was developed before the web

http://www.csmonitor.com/1981/0106/010603.html. He is still around at age 96 and does a radio show on Saturday mornings with another Hearth.com member. http://www.wvomfm.com/pages/20679749.php There are still a few hearth members who have Jetstreams which are a commercial version of his stove. At the time, wood was cheap and the commercial variants were expensive plus many of the installers were not familiar with them so after initial success and a drop in heating oil prices, they were no longer available. The design was 35 years before its time and I expect they would be competitive with the current crop of gasifiers. The bottom down burn design and loading arrangement is something that still hasn't been duplicated despite its advantages

 

[begreen]

There are several threads in the main hearth forum on Dick Hill and his projects. He has contributed a great deal to woodburning knowledge.
https://www.hearth.com/talk/threads/dick-hill’s-latest-adventure.52976/

 

[CountryBoy19]

I've run the numbers on Oak before (likely one of the worst woods when unseasoned) and at the fresh cut stage, assuming the moisture content was ~70%, only about 5-10% of the BTU's are consumed driving off the moisture. So why do we see such a drastic difference in burning seasoned vs unseasoned wood? You have to consider that the moisture keeps the fire from burning at a temperature high enough to enable complete combustion so not all the energy is converted into BTU's.

Furthermore we must examine who is burning unseasoned wood and who is burning seasoned wood. Most people burning unseasoned wood are burning in "smoke dragons" and even if they burned seasoned wood they wouldn't get complete combustion. That means their "returns" for burning seasoned wood are diminished. So it's a trade-off between marginal increase in BTU output vs. fire duration. On the other hand, those burning in modern EPA stoves can, and do see a difference in the BTU output between the 2 woods because their stove can take advantage of the dry wood.

Hopefully that helps clear some of it up...

 

[begreen]

Heat is heat. I can burn less seasoned wood in our old Jotul 602, but I don't. It may burn a bit longer but with less heat that dry wood and more futzing to get it to burn right.