MC of kiln dried purchased firewood

FionaD · Jan 6, 2015

i would really appreciate some feedback on this.....

I need to buy around half of my logs and since getting my first stove in Dec 2013 I always used the same supplier, who was very reliable. However the last two times I ordered from him his logs haven't performed so well... Some of the splits seemed too thick IMO - often 6 inches at the widest part.. But more to the point, the MC in the centre of most of these larger logs, when freshly split, was as high as 28%, even when the reading on the outside was as low as 16%. These are sold as kiln dried logs.

When I emailed him about this today he gave me a detailed reply, justifying the MC readings thus:

Regarding moisture content (MC), there are 3 ways in which to take moisture content, 1) Surface moisture with a Pin Meter in the centre of the log, 2) Split in half , we take 3 measurements one in the middle and one near each end, 3) Oven test we split a log into small kindling and weigh it and when we are sure the weight is static we calculate the true moisture content from there via spreadsheet. I attach a copy of the most recent Oven test and you will see where I have highlighted brown, that an Oak log recorded 28 in the centre when split, and ultimately recorded 18% when the Oven test was complete. The split MC recorded at 21% average of the 3 readings. Pin meters are not 100% reliable and MC varies over the whole log anyway so the acid test is always an Oven test which is 100% reliable.

Regarding Kilning, we take a kiln batch out after the surface moisture reads 12% 0r less, the Kiln is also computer controlled and we will know the MC of the air in the kiln at the end of the batch. If a kiln contains mixed Oak we would expect the oak to be 10-12% whilst all else would be below 10% normally. We then check MC regularly as the logs are being bagged and periodically do oven tests. Over time we know that when we have less that 10% surface moisture after a kiln cycle that the moisture by oven test will always be under 15- 20% for most species. However all logs will rise in surface MC after kilning, as they absorb moisture when humidity is high in the winter, and centre moisture content will migrate to a degree so your getting 20% on the outside and 28% in the centre would not surprise me dependant on handling and storage at your end.

On our website we guarantee less than 24% , so I don’t know where you got 20% although ours should always be well into the teens at least which gives us insurance so to spaek. Industry norm stipulates 25% or lower as being good for purpose.

What do you think of what he's saying? (I stacked these logs within hours of delivery in a covered shed with doors, so would be dismayed to hear that the MC might have increased significantly. Also..Is this 'true moisture content' measurement he descirbes an acceptable way to measure MC? My thought is to find another supplier, but I am aware I am still very much a newbie so he may be right and I may be doing him an injustice.

Thanks....

prezes13 · Jan 6, 2015

As far as I know you should take a measurement in a middle of a split right after you split it. That will give you the true read of its mc.

begreen · Jan 6, 2015

The moisture content should be well under 20% when the wood is resplit and tested on a freshly exposed face of wood.

Poindexter · Jan 7, 2015

Oven test is the gold standard. You need and accurate scale that measures mass to do it.

One potential problem with kiln dried wood is called case hardening. If the splits are too big and the kiln is running too hot the outside of the split can dry fast enough that some moisture is trapped inside the split and can't get out before the kiln cycle is complete.

Are your smaller splits dry all the way through?

If the business owner is reputable he will be glad to hear that one of his employees has been slacking and sending splits that are too big into the kiln. He will bring a truckload of dry all the way through wood to you, take your big case hardened splits back to his plant and have a staff meeting.

On wood that is air seasoned, the wettest part will be in the middle near the bark - unless one end got stood in a puddle for a while.

The oven test method corrects for distribution of moisture, you start with the absolute mass of the sample, bake it until the mass is stable or unchanged after more time int he oven, and then compare the mass of the original sample to the mass of the oven dried piece. Doesn't matter if most of the moisture was near the bark in the middle of the split, or all at one end after getting soaked on one end.

gyrfalcon · Jan 7, 2015

Poindexter said:
Oven test is the gold standard. You need and accurate scale that measures mass to do it.

One potential problem with kiln dried wood is called case hardening. If the splits are too big and the kiln is running too hot the outside of the split can dry fast enough that some moisture is trapped inside the split and can't get out before the kiln cycle is complete.

Are your smaller splits dry all the way through?

If the business owner is reputable he will be glad to hear that one of his employees has been slacking and sending splits that are too big into the kiln. He will bring a truckload of dry all the way through wood to you, take your big case hardened splits back to his plant and have a staff meeting.

On wood that is air seasoned, the wettest part will be in the middle near the bark - unless one end got stood in a puddle for a while.

The oven test method corrects for distribution of moisture, you start with the absolute mass of the sample, bake it until the mass is stable or unchanged after more time int he oven, and then compare the mass of the original sample to the mass of the oven dried piece. Doesn't matter if most of the moisture was near the bark in the middle of the split, or all at one end after getting soaked on one end.

Amen, and well said. I also get kiln-dried wood, and after complaints, my supplier has been giving me mostly smaller splits that are dry all the way through. The big lumber operation 30 miles from me that charges an almost literal arm and a leg for a cord of kiln-dried wood is able to dry even heuge splits that won't fit into my stove down to 20 percent or lower. The smaller folks can't do that unless they leave the wood so long in the kiln, they can't make a profit from it. So the choice around here anyway is between wildly expensive big splits, or reasonable cost for mostly smaller stuff-- max about 4 or 5 inches, which suits me fine given my fairly small firebox.

FionaD · Jan 7, 2015

Thanks so much guys... It felt good seeing all of your replies this morning. This forum is amazing!

It's good to get confirmation that (at most) 20% is indeed what I should hope for, even in the centre of a split.

Yes.... The smaller splits are <20% inside.

...but Poindexter, when you say -

Poindexter said:
The oven test method corrects for distribution of moisture.. Doesn't matter if most of the moisture was near the bark in the middle of the split, or all at one end after getting soaked on one end.

-do you mean that it is ok to quote an acceptable MC figure based on the average MC of measurements taken from several places, even if the core of the split is, say, 28%? Or are you just saying this is how it's done?

I have uploaded a copy of the oven test results he mentioned in his email. He has highlighted oak in the list becuase that was the last batch I had trouble with. My current batch is mixed hardwood in which the largest splits are not oak.

I will get in touch one more time and mention the case hardening possibility. Although I fear that, if they are a small company they may struggle to keep their logs in the kiln for longer, as Gyrfalcon has said.

The manager also said to me that quite a few folk have been asking for thicker splits. I think the poor guy is feeling the strain of trying to answer to everyone's demands.. Probably most,Mir not all, wood suppliers over here are small companies, relatively inexperienced and doing their best to cope with the sudden demand for firewood... Woodstoves are on the rise on recently over here and their use and the consequent demand for wood has increased enormously.

I did find another new company (there seems to be new ones every week) they seem to only offer larch though.. Calling it a hard wood, which I guess it is technically? Is larch ok to burn if it's not mixed in with other woods.. I heard it was pretty tarry....

blades · Jan 7, 2015

Well your first guy talks a good show. Random testing whatever method so not every piece is perfect. Point is its still high in the middle. That's a problem for you. Can you talk to him about keeping the split size down for you- might be your best way out. As with everything in sales, marketing has a license to stretch things quite a bit- consumer beware.
Got to love the kiln dried approach popping up all over- most are just baking to meet bug killing specs -ya it does reduce moisture content a bit but 4 or 5 hours at 160 degs isn't going to produce a true kiln dried all the way through the product. Oven test or no. More like two weeks to 30 days for a 6x6 of Oak. Ain't no way a firewood guy is going to be dumping that kind of cash into a resale product. Dang little margin in the first place.

gyrfalcon · Jan 7, 2015

blades said:
Well your first guy talks a good show. Random testing whatever method so not every piece is perfect. Point is its still high in the middle. That's a problem for you. Can you talk to him about keeping the split size down for you- might be your best way out. As with everything in sales, marketing has a license to stretch things quite a bit- consumer beware.
Got to love the kiln dried approach popping up all over- most are just baking to meet bug killing specs -ya it does reduce moisture content a bit but 4 or 5 hours at 160 degs isn't going to produce a true kiln dried all the way through the product. Oven test or no. More like two weeks to 30 days for a 6x6 of Oak. Ain't no way a firewood guy is going to be dumping that kind of cash into a resale product. Dang little margin in the first place.

My guy quickly got deluged with orders when he started up a few years ago, only some like me with EPA stoves that require really dry wood. He got enough feedback from.somewhat disappointed EPA stove owners, he went out and bought a bigger, hotter kiln, and all his customers just about swooned at the results, not just the EPA stove people. He intended to do this just as a sidelight to his chimney sweeping/repair/install, etc., business, but he's now close to having more demand than he can fill. He loads up the kiln on weekends and lets it cook for a week. Not sure what the temp of the new kiln is, but I believe it's more like 200-something.

I get my supply from him in early summer and stack it outside so it gets a few months of sun/wind drying, and it ends up at around 20 MC, a little higher for the inside of bigger splits, but still eminently burnable.

These small kiln-dried operations are the only hope for wider acceptance of new stoves, IMO, because there just aren't that many people willing and able to get 2 or 3 years ahead on firewood, or have the space to stack it all outside, and few firewood dealers can do that, either.

begreen · Jan 7, 2015

Larch is a common fuel out here in eastern WA. It burns well and is almost like hardwood. Just be sure it is seasoned to the core.

Kevin Dolan · Jan 7, 2015

begreen said:
Larch is a common fuel out here in eastern WA. It burns well and is almost like hardwood. Just be sure it is seasoned to the core.

Larch or tamarack is a soft wood species and as you say it does burn well. It is used for pulp wood and matures in the UK within 10 years for harvest. It loves wet soil and will grow to 30 feet tall in a short time and about 8 inch diameter for logs.

FionaD · Jan 7, 2015

Good to know about the Larch... Thanks BeGreen.. I thought a Pacific North Wester would be the one who'd know! I'll give the larch lady a call. I'm glad I found her actually, she is more local than the other folk and it turns out she supplies a pretty reputable stove shop, so that must be a good sign (I'm ever hopeful!) she also offers several choices of length of split which is rare indeed over here... Most bought logs are about 2 inches long - take it or leave it..(ok,I'm exaggerating a little there, but not much....)

I will pass on some of the good advice here to the other guy though.. I belive he is a decent type who is doing his best..

We've got a ways to go over here when it comes to stove and log lore.. We're newbies compared to Canada, the U.S, Scandinavia etc. I think it will be a year or three before all these new log suppliers appearing every week know what they're doing. But then maybe it's the same elsewhere and I'm just assuming everyone over the Pond has the same level of knowledge as everyone on this forum!

Poindexter · Jan 7, 2015

Fiona, I was just saying how it is done, pointing out the potential pitfalls.

If you are seasoning your own wood and keeping it covered on top you can open up a few of your typical sized splits, measure the MC in a few places with a pin type meter and you should fine the wettest part of the wood is in the center of the split, nearest the bark.

On some of mine for instance I can split a split one more time to look at what was the middle of the split, and I should find the highest MC reading at the edge near the bark, equidistant from each end. As I move the probe around and take more measurements the MC reading should get lower and lower as I move away from the bark edge and move towards the cut ends.

However, if a split was just thrown into say a windrow or similar random pile, I might find a piece that had one cut end in ground contact all summer while the other end was up in the air. On this particular piece I might find the wettest part of the split to be the end that was in ground contact all summer.

Using my pin meter and checking the MC in the "usual" places I might miss the extra water at the end of that split and end up with a damp piece of wood in the stove.

Using the oven method, I would know the mass of the wood before and after oven drying, but I would not know where in the split the water was concentrated before oven drying.

Fiona, do you have any lawn space with good sun exposure? In the states at least wood burners really start saving money on heating bills when they can buy green wood and season it themselves. Takes up some space, but really renting whatever amount of realestate is why seasoned wood costs more than green fire wood.

28% wood does not go in my stove. If one makes it in there, once it gets to hissing and blowign steam I'll toss it out into the snow and give it another summer on the drying rack before it gets a second chance going in the stove.

FionaD · Jan 7, 2015

Thanks Poindexter... I just wanted to be sure you weren't saying it would be ok to burn a split that was 20% on average but 28% inside, I hear now that you're saying that would not be good, no matter what the average readings say.

I smiled when I read you asking if I had a good place with sun exposure! Even if I had the space I wouldn't be able to order the sunshine I'm afraid, I'd be out there several times a day on some days, rolling the tarp on and back off that wood! I really wish I had somewhere to season all of my own wood. I honestly can't imagine it would even be possible in this country to season wood outside, even if one had enough space... Anyone I know who seasons their own for selling has it sitting in a huge barn with air blowing through.

On the plus side, we're a tad more temperate all the year round than many places (such as Alaska!) so i won't be needing to burn nearly as much wood to stay toasty.. We've only been below freezing for about 7 days in total so far this winter.. :cool:

Poindexter · Jan 7, 2015

Fiona, I am not familiar with the Jotul F3cb, but I don't know of any stove that will run OK on 28% that doesn't run better on 20%.

The other thing to consider is the "average" moisture content of a piece of wood. If you got a little tiny spot of 28% at one end that drops off quick 26-24-22-20 % going end to end and 3/4s of the total piece comes up 20% with a tiny bit of 28% at one end, sure burn it.

But if you got a 20% shell with a 28% filling it sounds case hardened to me. Just split one open to see how much of it is at 20% and how much of it is 28%. Can you find any area at all that is 22 or 24%?

FionaD · Jan 8, 2015

I see what you're saying .. Thanks so much. I will certainly mention the case hardened thing to the guy... For sure he would want to know about that if he cares. I will also make several splits of each of two or three of the larger pieces of wood and take several MC readings, that will indeed be interesting!

FionaD · Jan 8, 2015

Kevin Dolan said:
Larch or tamarack is a soft wood species and as you say it does burn well. It is used for pulp wood and matures in the UK within 10 years for harvest. It loves wet soil and will grow to 30 feet tall in a short time and about 8 inch diameter for logs.

Thanks Kevin, I missed your post till now, I think we posted pretty much the same time. Yes, lots of larch growing commercially round here... I look forward to comparing how it burns to the hardwoods I've been using so far. I guess I will get through it a little quicker, but that's ok it's also much less expensive to buy!

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MC of kiln dried purchased firewood

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