How dry can seasoned logs get?

[wardy]

I find this thread and other threads about the moisture content of logs funny, people are getting to anal about bloody wood! We have burnt wood since the start of time and I doubt they had a blinking moisture meter back when cave men were using fire as heat. Get some wood and hold it in your hand, if it's wet then leave it if it's dry then burn it. The whole firewood market is a joke, people brainwashed into thinking softwood is crap. Well your wrong, the Scandinavians burn pretty much only softwood and they happy enough. This is one of the reasons I'm getting out of logs, people are getting way to fussy about what they burn.

 

:thumbup:Spot on We should all be educating customers to buy more softwood to burn . Its all i ever burn because i find it tough to sell, So i sell hardwood to the firewood snobs .

[cornish wood burner]

:thumbup:Spot on We should all be educating customers to buy more softwood to burn . Its all i ever burn because i find it tough to sell, So i sell hardwood to the firewood snobs .

I think we are all agreed that education is the key so I would like to add

to the Spacemans post.

The theroretical energy loss due to moisture is far different to the actual one. Apart from the energy needed to evaporate the water, the flue needs to be of sufficient temperature to prevent creosote forming so as he says the fire needs to run hot resulting in a lot of heat going up the chimney. A modern efficient wood burner running on 30% MC wood burning hot with an insulated flue should be able to achieve high enough temperatures. The problems come with uninsulated flues, stoves that are shut down, inefficient appliances or worse still open fires. Dry wood is definitely desirable for the less than perfect burning conditions and equipment.

[openspaceman]

I think we are all agreed that education is the key so I would like to add

to the Spacemans post.

The theroretical energy loss due to moisture is far different to the actual one. Apart from the energy needed to evaporate the water, the flue needs to be of sufficient temperature to prevent creosote forming so as he says the fire needs to run hot resulting in a lot of heat going up the chimney. A modern efficient wood burner running on 30% MC wood burning hot with an insulated flue should be able to achieve high enough temperatures. The problems come with uninsulated flues, stoves that are shut down, inefficient appliances or worse still open fires. Dry wood is definitely desirable for the less than perfect burning conditions and equipment.

 

I don't think we disagree on anything here.

 

The question then is why do you want to dry stuff?

 

Air (=solar power) drying is the most economical and seems to be the way many woodchip suppliers are going (stacking partially debarked roundwood and then chipping into dry storage). Has anyone a link for the LENZ system to save me unfruitful googling?

 

Farmer Rod was chipping into a barn and then shovelling it about to expose fresh surfaces, I don't know what mc he got down to.

 

Chip in a covered heap will dry but you must prevent the rising moisture condensing in the upper layrs re wetting.

 

An earlier poster suggested a figure of £9/tonne but did not specify the before and after mc, we aimed for £10/tonne water removed in 2002.One of the big costs with the drying floor was the higher fan costs because of higher back pressure from chip compared with grain which is more uniform but this was not my field, we were drying logs which presented different problems. Chip looked easier because of the quicker throughput and consequential lower system losses.

 

BTW creosote is a result of pyrolysis, the gunk in a chimney is a mixture of condensed tars and PICs and if the burn is clean they don't get produced.

 

BTW2 openspaceman is a play on Viv Stanshall's song.

[Stubby]

 

BTW2 openspaceman is a play on Viv Stanshall's song.

 

Ah but " here comes the twist , I don't exist " .... BDDDB

[mikeyne]

I used this graph when I was trying to work out what moisture content I should expect from air dried seasoning of our wood pile:

Even in winter at 90% humidity (the black line), the wood should be stabilising to around 22% moisture. It does not take many dry days in summer to see the equilibrium moisture level getting down to 15% moisture (the blue line if we are really lucky).

 

How long the wood takes at that state to get down to the equilibrium is the big question - I actually found a research study that had looked into this from the perspective of forest fires (how many hot summer days would it take to turn a forest floor into a fire risk) and this could be reapplied to wood drying. So if you held a kiln at such a temperature and humidity you should be able to predict the time to dry from one moisture level to another.

 

I had a bit of a surprise recently when I brought some of the wood down into the boiler room. All summer it's been drying in a poly tunnel and cracking nicely, getting to 15 odd % on the outside and 25% inside if freshly split.

 

However, I noticed that since the end of summer, the cracks have disappeared on the logs and when they come inside they look like this:

 

But after only 11 hours in the warm dry conditions of the boiler room they look like this:

It seems they will respond quickly to changes in ambient conditions.

[openspaceman]

Ah but " here comes the twist , I don't exist " .... BDDDB

 

[openspaceman]

I used this graph when I was trying to work out what moisture content I should expect from air dried seasoning of our wood pile:

[ATTACH]169435[/ATTACH]

Even in winter at 90% humidity (the black line), the wood should be stabilising to around 22% moisture. It does not take many dry days in summer to see the equilibrium moisture level getting down to 15% moisture (the blue line if we are really lucky).

 

How long the wood takes at that state to get down to the equilibrium is the big question - I actually found a research study that had looked into this from the perspective of forest fires (how many hot summer days would it take to turn a forest floor into a fire risk) and this could be reapplied to wood drying. So if you held a kiln at such a temperature and humidity you should be able to predict the time to dry from one moisture level to another.

 

I had a bit of a surprise recently when I brought some of the wood down into the boiler room. All summer it's been drying in a poly tunnel and cracking nicely, getting to 15 odd % on the outside and 25% inside if freshly split.

 

However, I noticed that since the end of summer, the cracks have disappeared on the logs and when they come inside they look like this:

[ATTACH]169436[/ATTACH]

 

But after only 11 hours in the warm dry conditions of the boiler room they look like this:

[ATTACH]169437[/ATTACH]

It seems they will respond quickly to changes in ambient conditions.

 

What's the attribution for the graph?

 

There are a couple of points from this, one being that even though an equilibrium will be reached given sufficient time at low temperature much more air has to pass over the log. The other that drying below 15% is wasteful and EMC can regulate this.

 

The thing about wood below the fibre saturation point is that there is shrinkage and swelling as moisture content changes, different woods behave differently. In general there is little length change, most change is tangential to the grain and it is this that is causing cracks to open and close

[mikeyne]

I got it off Wikipaedia:

 

http://http://en.wikipedia.org/wiki/Equilibrium_moisture_content

 

For the cracks in my logs, I'm assuming that they took a while to develop over the summer and now we are heading towards the cooler wetter months, the wood is regulating as you say and they are closing up.

 

I suppose this has an unexpected benefit as it closes the surface area available on the logs so they will absorb moisture at a slower rate. Regardless, even though they have closed up the surface moisture content at the end of the logs is still a nice 18% so the poly tunnel is keeping them pretty dry even in winter.

 

Agree it is wasteful to dry below 15%, as winter storage will generally overide it.

 

I've found the poly tunnel has taken green wood at around 45% moisture (sycamore and beech) and taken it down to an average of 25% over a period of 6 months. But this is for logs that are 60cm long and densely stacked in 4 rows. There is lots of air flow around and through but it is not as good a drying environment as it could be (the logs on top got ridiculously dry in a few months).

 

I'm hoping that there will be enough storage for two years supply so next year, the wood will be awesome, it's already good this year.

[cornish wood burner]

Hi Mikeyne Your poly tunnel sounds good. Have you put in vents either end to get some air flow through. Probably closed in winter open in summer. One point in winter we have more night than day so I expect that is mainly at night when the moisture is reabsorbed. Lower night temps and the RH will go to 100%. Certainly does in Cornwall, 98 % by day as well ATM.

If you could get a stack of wood to its expected minimum mc at the end of summer it might be an advantage to cover the logs with polythene /insulation to restrict the moisture being reabsorbed. Not tried it but it might be an interesting experiment.

[teepeeat]

Hi Mikeyne Your poly tunnel sounds good. Have you put in vents either end to get some air flow through. Probably closed in winter open in summer. One point in winter we have more night than day so I expect that is mainly at night when the moisture is reabsorbed. Lower night temps and the RH will go to 100%. Certainly does in Cornwall, 98 % by day as well ATM.

If you could get a stack of wood to its expected minimum mc at the end of summer it might be an advantage to cover the logs with polythene /insulation to restrict the moisture being reabsorbed. Not tried it but it might be an interesting experiment.

 

mmm, would have thought that unless you can seal it completely, moisture will get in regardless??