UKH

I guess quite a lot of people on here use log burners, as we do. I realise that using these in urban areas is seen as a bad idea for pollution reasons but as we are in a rural area we intend to carry on. 

We have a choice between logs dried in a barn (which they claim gives a moisture content of about 30%) and kiln-dried logs (more expensive, but 20% moisture claimed). To me, it seems using energy to season your logs is not very "green", but drier logs are less polluting we are told. Then there is the question of storage. We store our logs outside but under cover, but I strongly suspect that if I stored kiln dried logs this way they would end up absorbing moisture from the air so I will land up with logs no different than the barn dried ones (which are of course also cheaper). Any thoughts on this? 

Personally I would take the air dried every time, but I store outside.

May I suggest you pick up a copy of Norwegian Wood - Chopping, Stacking and Drying wood the Norwegian way.

It has more info of wood burning than I though possible, and a thoroughly entertaining read as well

Are those numbers definitely correct?  I'd alway aim for below 20% when burning and can achieve this by air drying outside in a wood store with slatted sites and a roof.  Similarly when buying in logs we've had both kiln and air dried, but moisture content is typically high teens.

From an energy point of view air dried will obviously use the least, but kiln dried may not be particularly bad if waste heat from another process is used for the drying.

You live in a swamp? Air dried you should be around 13-15% and kiln dried 10-12%. For the kiln dried it takes ages for them to absorb water to get up to air dried, probably six months or so, I'll measure some this afternoon (we've drying plant where my workshop is). The timber in my barn is at 16.9%.

In Germany burning at over 20% is anyway illegal and economics of kiln drying to 12% make the process a net win over burning at 20% to say nothing of the air cleanliness benefits.

you will be using energy to dry your logs in the log burner.

Environmentally it comes down to your specific interests....

Greenhouse gases

- drying them in your logburner as part of the combustion process reduces the efficiency. As you are using a carbon neutral fuel this is irrelevant.

- if the supplier uses biomass to dry the logs its carbon neutral, if they use fuel oil etc then its worse, if they use renewable electricity its neutral and if they were to use a theoretical negative carbon electricity (biomass with carbon capture and storage) it would be carbon negative (better).

Local air quality

- Burning dried wood will probably give better combustion with reduced particulate soot and CO. It might burn hotter though which would give added NOx which is bad.

- Dried wood should give lower consumption due to higher useful energy per kg so less local air pollution.

In summary - it depends on the kiln fuel and whether you are more interested in the health of local children OR all children

Store logs outside in single line stacks with a plastic sheet on top. Allow the air to circulate freely around the logs. The important thing is to get rid of the sap, which barn drying tends not to do. It is the sap which creates most of the tar. Water damp reduces the calorific output of the wood, but is not as bad as the sap. Buy winter 2021/2 wood now and get it stack outside. Try to obtain hardwood logs, as softwood is a bigger volume so less energy per stoking, and softwood also has more resin and is harder to season properly. (FYI I spent the end of the 70's and 80's in the woodburning industry, designing and building high end stoves as well as selling them!)

Ensure you run the stove flat out for at least 1 solid hour per week, to keep tar deposits down (effectively having a very small chimney fire instead of it building up and having a big chimney fire.)

Check with the house insurers how often they recommend having the chimney swept, but at least once per year, but some specify twice. Keep receipts because if you have a chimney fire or any other stove problem they will use lack of cleaning as an excuse. 

Thanks for the interesting and informative replies. There is just so much expertise available on this site, whatever the subject!

I've still got to make a decision.

Can't see me buying logs a year in advance, though, John. Not at my age.

Half and half?

When I was burning wood I used mostly oak & ash which was seasoned for at least a year before use.  As someone said, burn hot at least once a week.

Incidentally my oak beams came from Canada and used for transporting heavy plant, and would go on the factory bonfire!

All of the firewood I have is barn-dried and it burns superbly.
I’ve just filled up the inside stores at home with some beech & ash I cut/split last summer and have had drying ever since in the barn, and it’s dry as a bone. 
With regards to the kiln-dried stuff, as soon as you stack it at home it’ll absorb ambient moisture anyway so won’t end up any drier than decent barn stuff. 

Seconded. 

Buy a moisture meter. Legally wood should below 20% but i wont burn above 17%

We source fresh logs which we split and air dry at home, no issues getting down to low teens of you have the patience. No way I could justify kiln dried, can't see how that can tick the green credentials. 

We bring seasoned wood into the house to air dry for at least a week before burning. Just stacked next to the chimney and saves going out in the cold/rain when you need another log. 

I store all my logs outside for a couple  of years under plastic. Then stored in a dry shed for another 6 months. Three baskets are kept indoors for weeks before they are burned, then a log or two are kept in front of the fire when it's lit.

Lovely and dry when used.

Risk of chimney fires much diminished with inox pipe system

never heard of dried wood taking back moisture - if correctly protected, I mean air contact only.

Kiln drying sounds like a stopgap short term solution; plan ahead and get organised

Seasoning is about losing sap and yes once that's gone it can't return. But logs will take on dampness from the air, just simple water but enough to reduce the heat output of the logs.

Traditionally you would sesson outside where well ventilated in a covered rack with open sides, then once seasoned move the dry logs to a woodstore which protects from rain and snow. 

Spending years playing with old wooden boats, I can assure you that wood absorbs moisture from the atmosphere. The amount a boat moves (contracts/expands) during season changes is quite impressive.

The "sap" doesn't leave the wood when it's seasoned conventionally, the water in the sap evaporates leaving nearly all the soluble components like the sugars and minerals behind. In contact with moisture in the air the wood will take up water again until it reaches equilibrium but this is a slow process, the sapwood channels fill quite quickly but the cell water uptake is slow.

not to worry, firewood sheltering methods have reliably refined over millenia; it wouldn't be v practical to bring the next 2 yrs supply into your house anyway  

Interesting. 

I know we have one rack which when last tested was around 15% but after this moorings rain was soaking wet. Experience tells me that it just needs to dry off (rather than season for months) for it to be ready to burn. 

The exposed surface isn't where you get any reliable measure of moisture content, especially if you go into the sapwood. You should split the piece and cut it in half then average the readings from the heartwood and sapwood. Commercially it's also done by weight.

For boards air drying the rule of thumb is 1" per year which is why a lot of firewood is dubious! Kiln dried it's easier to get good results.

Yes 15% would be when freshly split. Outside surface I think can be technically described as soggy. 

Just have a tight-fitting internal door like I have in my house - it regularly absorbs enough to start binding.

i wouldn't be too worried about dry wood absorbing moisture unless its kept in crap conditions.