Moisture Meter

I'm wanting a basic meter fro checking the moisture level in timber
for my log burning stove - does anyone have any experience of the
inexpensive ones on Ebay ? And what is the significance of 2 pins or
4 pins ?
I did wonder about some sort of way of using my DVM, but the Ebay ones
are so cheap that buying one in seems a better option.
Rob
Reply to
robgraham
I'm wanting a basic meter fro checking the moisture level in timber for my log burning stove - does anyone have any experience of the inexpensive ones on Ebay ? And what is the significance of 2 pins or 4 pins ?
I did wonder about some sort of way of using my DVM, but the Ebay ones are so cheap that buying one in seems a better option.
Rob
Reply to
robgraham
Is there a specific moisture level quoted for log stoves?
Do you need a calibrated ruler fro measuring the length and diameter of the logs?
;-)
Reply to
Frank Erskine
You can get a nasty resistance meter for about =A310 in DIY stores - that will do you for that purpose or you can roughly estimate the volume and weigh it to get the density and work out what it should be were it dry (using species denstity tables) and hence cacluate the MC W/w
once you have done this for a few months you wont need to weigh it and will be able to heft it in the hand and estimate! Chris
Reply to
mail
Not really - my flue blocked and cost a lot of money to get sorted. The chimney man was of the opinion that wood that was dry enough was a possible cause - the other was only getting the flue swept once a year.
I've got a complete beech tree for logging - it died 15 months ago and fell 9 months ago, so I'm interested in how dry it is in comparison to some other logs I have, and the cost of a basic instrument is peanuts in comparison to the last repair bill.
Rob
Reply to
robgraham
I've spent around 40 years on housing maintence and dealt with many chimney problems and that's the first time I've heard that.
As a matter of interest and for safety, your chimney should be swept at least once a year anyway and twice would be better - carbon monoxide is a killer.
If the tree has died, then after around 15 months, the only moisture in there is going to be from the rain, if it was put under cover after it was felled then it should be dry enough to burn surely?
I am not an expert on wood burning stoves so I am open to correction for any errors.
Brian G
Reply to
Brian G
In message , robgraham writes
I presume you mean "wasn't dry enough"
So it was blocked by water vapour ?
Then cut it, split it and stack it
How do you know that where you measure will be representative of the moisture content ? The heart wood will take much longer to dry out than the surface where you can measure
Reply to
geoff
In message , geoff writes
There is an expert in here somewhere.....AJH?
For what it is worth, my experience of closed wood burning appliances is that the high exit temperature leads to condensation of unburned volatiles in relatively cold flues.
When there was ample Elm to burn, this residue was a tarry material which migrated through unlined chimneys and discoloured your plaster. It was also very difficult to sweep.
One or two of my acquaintances have recently installed woodburners despite being in built up areas and presumably subject to smokeless zone regulations. I think it is linked to some carbon footprint issue which does not seem to have been carefully considered.
regards
Reply to
Tim Lamb
Double skinned insulated ones are de jure these days for this reason.
same for all wood, Not just elm.
Reply to
The Natural Philosopher
On Sun, 18 Nov 2007 09:45:09 +0000, Tim Lamb wrote:
Idontdoexpert!
There are many ways to deposit stuff in the flue. The black shiny tarry deposit is quite different from soft soot. I think the latter is a result of temperatures enough to achieve good secondary combustion but too little secondary air, a bit like driving a petrol engined car with the choke out (probably not possible with ecu and fuel injection). The shiny tarry stuff is volatile products from the pyrolysis process, that have been driven off by the combustion of fixed carbon of a smouldering log and as you say condensed on hitting a cold chimney surface, this is why it is important to both have good combustion and a warm (150C+) chimney. Basically if you see white smoke you have wet wood and pyrolysis products going up the flue, blue smoke and you are reaching secondary combustion temperatures but putting PICs (products of incomplete combustion) up the flue, no visible smoke and you could be achieving good combustion but equally you may be releasing a lot of CO from the latter stages of combustion.
Yes, you can actually often see this on the outside of chimneys on old houses, many of the volatiles will be water soluble and acidic, pyroligneous acid was made commercially by condensing the offgas from hardwood pyrolysis, it's a mixture of vinegar, methanol and other worrying substances.
It is possible to buy stoves that are exempted under the clean air act. Also greeny points are scored in planning applications for using carbon neutral heating. I service the heater in a block of flats in Brixton and a large retail store where I doubt strict economics dictated the use of wood fuel. Mind with oil at GBP300/tonne and gash wood harvested at GBP15/tonne there is scope for savings.
RE the op's question; I think these moisture meters with probes are simple resistance meters, they depend on the electrical path through hydrated salts in the wood??
The thing is a log dries slowly and from the outside inward, so a surface reading will mean nothing. Also there are two different ways water is associated with the timber, the first is the cell water and the second is the water associated with (weakly bonded to) the cell structure. You have to dry the wood down to the stage where total water is 30% of the total weight before you affect the latter and this is the stage where drying gets more difficult.
The only safe way to judge water content is to put a small log (no dimension >150mm) into an oven at about 120C for 24 hours, or less if you log the weight drop graphically. It can be done quicker in a microwave but the temperature must be kept below 230, the hot steam can initiate pyrolysis, the give away is the more copious white cloud given off plus the tangy smell of vinegar.
The simplest judge for whether hardwoods have fallen below 30% mc wwb is to see if you can blow down the grain.
AJH
Reply to
AJH
The Natural Philosopher wrote in news: snipped-for-privacy@iris.uk.clara.net: OK
logs!
get sorted.
enough
flue swept
months ago
in
basic
bill.
representative of the
dry out
appliances
unburned
this reason.
material
your plaster.
woodburners
smokeless
footprint issue
Reply to
John Smith
In message , AJH writes
You are going to have to explain this:-)
BTW I have a chap coming in early December to mill up my bits of dead Oak. Do you have any idea of the work rate for a Lucas mill cutting 4"x3.5" in dry Oak. I'd hate to pay a days work and find he had finished by lunch. I can go and find another tree if necessary.
regards
Reply to
Tim Lamb
In message , robgraham writes
As I said before, you will only be able to measure the moisture content of the surface, which will be more a function of how and where it is stored than how wet the heartwood is
As someone else said, you really should be getting a chimney swept annually
No, it takes months, which is why you should split / prepare in good time and stack them
Reply to
geoff
In message , robgraham writes
You could probably adapt a moisture meter designed for cereal moisture measurement.
The rather dated industry standard was made by Marconi and the earliest versions vacuum valve amplified. I have one gathering dust in the workshop:-)
Ground cereal (sawdust) is compressed in a chamber and the chamber resistance used as one arm of a bridge balance. You would need to calibrate the scale for wood and there is likely to be a variation between species. I suppose Andrew's oven/weighing method could give a series of readings ......
Given the range of tree species you may find life is too short.....
regards
Reply to
Tim Lamb
On Sun, 18 Nov 2007 21:38:01 +0000, Tim Lamb wrote:
If the log is has dried to
This is a circular saw where the saw head moves along the log in one plane and then the head is turned 90 degrees and makes a second pass to produce a cant with at least two sawn faces?
I doubt we cut much more than 150Hft/day on the woodmizer but potentially the lucas could do better if you are cutting these 4x3.5 because there's much less rehandling of the log, you just remove the cut board. What worries me about this lucas method is it is less able to make allowance for defects, great for straight clean timber though.
AJH
Reply to
AJH
In message , Tim Lamb writes >In message >, >robgraham writes > >>OK, a moisture meter is not really the way to go. I may well get one >>anyway as they are cheap enough (and correspondingly possibly useless >>therefore!). I have some beech logs which are old and have been under >>cover for some time so can be used as a reference. And the current >>splitting process has produced logs of different thickness so I can >>get a figure on pieces that are quite a small cross section. >> >>Very many thanks to those that have been helpful. I'll post back in >>due course with what I find - curiosity comes into it quite bit too. > >You could probably adapt a moisture meter designed for cereal moisture >measurement. > >The rather dated industry standard was made by Marconi and the earliest >versions vacuum valve amplified. I have one gathering dust in the >workshop:-) > >Ground cereal (sawdust) is compressed in a chamber and the chamber >resistance used as one arm of a bridge balance. You would need to >calibrate the scale for wood and there is likely to be a variation >between species. I suppose Andrew's oven/weighing method could give a >series of readings ...... > >Given the range of tree species you may find life is too short..... > exactly
Reply to
geoff
Blocked flue might also be down to insufficient air to burn the wood cleanly, especially if the stove has been 'closed down' to make the wood burn for longer.
If logs have at least started to season the ends 'check' making them much easier to split.
Comparing moisture readings along the split wood should give some idea how well they've dried right through.
cheers, Pete. cheers, Pete.
Reply to
Pete C
Look Geoff, I came to ask a simple question and I didn't come to be preached at by a pompous tosser. How do you know that the flu wasn't being swept annually - you just assumed it and issued me with an instruction to do so.
How do you know that I don't split and stack in good time - you just assumed it and issued me with an instruction to do so.
I didn't say that I've been burning wood for 20 years because I didn't think it necessary. All I asked was an opinion on moisture meters because it seemed a possible answer to the chimney man's comment.
I've now received the opinions from better men than you, that in likelihood it won't tell me much, but I didn't need to be told anything else.
Rob
you just assumed it. It was possibly a throw away comment by the chimney man as equally he said it could have been a bird's nest
Reply to
robgraham
On Sun, 18 Nov 2007 22:19:20 +0000, Tim Lamb wrote:
The energy content of most species is similar, at the same moisture content per unit mass, though softwoods are a bit higher, even though their initial moisture content and density makes them less attractive.
Now given that their form makes them easier to harvest, and the harvester on my site currently, near you, is felling, snedding and crosscutting them at a rate of >30m^3 of round timber an hour and the total harvesting cost to roadside is GBP11/m^3, softwoods should represent a cheap energy source even conventionally harvested.
AJH
Reply to
AJH

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