dry vs moist wood for burning

I would like to know your experiences burning incompletely dry wood in batch heaters . Does mixing dry wood with some greener wood work? How does it affect the burn cycle?
Are there some heater cores more forgiving in this respect? And which style heater core absolutely hates burning slightly green wood?
What method to you use to dry your wood faster than having prepared it last year?
Thanks for your input
Costi R

Paul made a couple of podcasts about this. I've shared the links and also the summaries so you can see what's in each one.

Podcast 729 - How to Heat Your Home with Green or Wet Wood - Part 1

Paul starts out by stating the wisdom that you should only burn dry wood.  However, sometimes you need heat and you don't have any dry wood - sometimes, you have to use wet or green wood but burning green wood is not a good idea - what you need to do is dry the wood fast.

Using wet or green wood for heating is a lot of extra work.  If you really need heat now, you can also burn cardboard or paper waste.

Having a place to store wood makes a big difference, especially if you can store the wood indoors so it dries better.  You can get or make crates to store wood.  Stacking wood on end makes it dry much faster; also cutting the wood down to smaller sizes makes it dry faster.  Cutting the wood shorter also helps.

Paul uses crates to hold wood, which can be brought inside to dry faster.  They're great for stacking wood to dry in, you can stack them around the stove, a couple feet away.  You shouldn't put wood right against or on top of the stove as it's dangerous, it can emit fumes and could even catch on fire.  By using all these tips wet wood can be dry enough to burn in just a few days.

Samantha joins in.  She has lived in the Pacific north west where wet wood is common.  She says if you find a dead tree which is leaning, the underside of it can be drier and also the inside of the wood can be drier, even if it's been in the rain.  Split off the outside of the wood to leave that to dry more while you burn the inside parts.

Podcast 730 - How to Heat Your Home with Green or Wet Wood - Part 2

The question is asked about burning green wood in a Rocket Mass Heater.  Paul feels that it wouldn't get hot enough to burn off the creosote and smoke as it should.  With that said it is probably safer to burn wet or green wood in an RMH than in a regular stove, but you still should avoid burning green wood at all.

The best plan is still to dry the wood as much and as fast as you can.  You need to establish a system to process the wood and to know which wood is ready to burn and you will have to store a LOT of wood inside.  It will be more work and you need to plan.

Further to the problem of heating your home, There are other things you can do to help reduce wood use.  You can stack wood near the stove, but leave at least 18" space.  You can fit angle iron to the top of the stove to make a rack to stack rocks above the stove to store heat for overnight.  It's important not to put stone directly on the stove, the angle iron allows about a 2" gap for air to circulate and avoids overheating the stove top.  Especially with a steel stove, getting it too hot is bad for it.  If you have power, you can use a fan to create air movement to dry your wood faster.

Another contributor asks about how thick a brick mass can be.  Paul feels if you stack a single layer of bricks it will work well - it needs a gap between the bricks and the wall.  If you stack more than one layer the heat won't conduct well unless you use cob or other material to bond the bricks together.

Finally a contributor asks about heating a small home - they are trying to heat 600 sq ft.  Paul feels that with a simple wood burner, that can be a challenge.  Adding some mass could help even out the heat.

I saw this guy on Youtube build a solar-powered firewood kiln: https://www.youtube.com/watch?v=eMI40iFx8KE

Wonder if just a passive solar setup could work too, like the jerky solar drier?

Costi Rado wrote:I would like to know your experiences burning incompletely dry wood in batch heaters . Does mixing dry wood with some greener wood work? How does it affect the burn cycle?

First of all: start a batchrocket with dry fuel. Once the firebox and afterburner are thoroughly hot, the system doesn't care as much whether the fuel isn't dry or not. It does affect the burncycle, though. The moisture need to be driven out before the fuel is properly off-gassing. This process will drag down the efficiency of the burn greatly, even as far as half the energy contents of the wood.

Costi Rado wrote:Are there some heater cores more forgiving in this respect?

Yes, it seems that the latest Shorty batchrocket core is quite good at that. Also, the larger the heater, the less it is hampered down by fuel that contains 25% or even more of its weight as water.

There's also a peculiar phenomenon I've seen and heared with moist fuel in particular: the afterburner "rockety" sound seems to be much louder. And through that roar at the same time a very low, irregular rumbling, that makes one think about a large diesel engine that's running outside. Hard to describe, this effect is stronger in a first-generation batchrocket, one without a door of any kind.

Only slightly related, but could one burn trash/plastic in a RMH if it burns so hot? Obviously even better not to create trash in the first place, but would that work or be a stupid idea?

One observation I'll add is that even dry wood gives off lots of water vapour when it burns. This is why the ideal RMH exhaust is mostly just steam. You can run into problems with wet fuel if your draft is marginal, especially in the shoulder seasons and when the mass hasn't heated up yet, because that water can condense out of the flue gas at the point where it cools enough, causing a plug effect. The other thing I have noted with my greenhouse J-tube is that if you're not running it all the time, those condensation episodes will rust out steel flue pipe and barrel surfaces.

I have "dead" space around two sides of my RMH bell, and stack it full of firewood to dry. It can hold at least half a cord, and even wet or green wood split well and stacked for air circulation is bone dry and ready to burn in a month or so of winter burning. I just have to have some already dry to start the season. I can stack quite a bit on top of the bell (which has 6-9" thick roof and sides) and dry it in a few days. Wood stored like this seems to lose almost half of its weight from a damp state, and bursts into flame almost immediately when loaded.

This can be as complicated or as simple as you want it to be.

in the very simpliest terms --- Burning wood that is 10% moisture vs 25%  produces about 83% as much heat.  Again this is a very simple calculation of just calculating how many pounds of wood your actualy burning.  90# vs 75#  if your starting with 100#   If your calculating in metric, the same 83% comes forth.  

Ironically this 83% figure remains about the same with good oak vs poor cotton wood. If you start with the same wood and maintain the same spread in moisture, the figure does not change much.
Likewise the effcieny of the stove does not effect the number much.

WE can wish for better, and precieve it to be better, but in this case, just not to be.

Now for a bit more complicated, for every pound of water your converting to steam, cost you 992 BTU's.   So above this is 15 lbs of water for every 100 pounds.
So  an additional 14, 000 btu's out the flue.  No getting around it.  If it is there (the moisture)  and your wood burned, then it consumed the BTU's to turn to vapor.  

Stay warm folks, and let the suns drying power in the summer give your stove heating power in the winter.

Scott

Thanks for the great suggestions so far, there's so much to look into.
First, the old thread from this very permies site, I'll read it thru to learn things I may not already know (like storing the wood vertically).
Then the YouTube video, I didn't know about it even though I recently discovered this same channel and subscribed to it, he had some excellent videos recently about making solar hot air collectors. Maybe those can be coupled to a solar kiln for drying wood.
And thank you Peter for your info, it's great to know that once already heated with dry wood, you could also add some greener wood to the burn chamber in your shorty batch heater. I'll have to investigate that design, so far I haven't as I'm very busy with a major renovation of a bedroom before winter sets in.
But all these responses are great, within the next few days I shall finally receive the firewood I ordered months ago. I usually prepare my own, but this year, due to some special circumstances, I only prepared about half the wood, and ordered the rest. That's why I anticipate I may have some greener than usual wood to deal with this winter, will have to try to dry it as much as possible before heating season starts about November. Will also have to preserve as much already dry wood to start fires with later in winter...
Thanks again for all your responses, I eagerly come back to read and learn from all your suggestions whenever I get the chance. It's a great community you have here, thanks for all willing to share.
Costi R.