Pete Bannister

i agree with Farmer Tom , the intertek document is useful. The point about moisture meters being inaccurate when wood is above fibre saturation is also partly true however, Above 50 % m.c for most species and the reading it questionable. But you can obtain fairly accurate info in the range 28% ( the commonly accepted fibre saturation value) and the high 40%'s ime. Another point, although its accepted that meter prongs should only be used perpendicular to the timber, I’ve never found any measurable difference when testing the parallel to grain. So I think this is one of those 'facts' that get repeated without being independently tested ..there's a lot of that!

I use moisture meters almost daily in my profession and have done so for over 25yrs . There are a few basic points to note that may be of help: 1.for timber, you will be best served by a two- pronged meter that measures electrical resistance ( conductivity). 2.Buy one that you can easily obtain replacement probes for because you will break or distort them. 3.Get one that measures % moisture content. ( ie gives a % read out). Almost all but the cheapest do this. Most of them are designed to a sensitivity of +/ - 2% ( ie 4%) overall and the 'top end' ones will be more sensitive than this, even though they still quote these parameters. 4. Self-calibrated meters are not such a good idea. The more expensive meters are supplied with a calibration check device ( a wire strip of know dielectric resistance). Checking reading by testing something of a know m.c ( e.g. dry, internal joinery in a heated dwelling will generally be between 4%-9% mc.) is a good habit. 5. Surface readings are not very helpful. For wood fuel you need the general moisture content. So, in a pile of logs you need to take a number of samples throughout the pile and calculate a mean average. You need readings from at least 50 mm below the surface of a piece. So split the logs, and you can take readings across and along the section to get a really precise overall value for any one sample. The more samples you take, the better picture you will obtain. Beware that a surface reading can be totally misleading either way. 6. The point previously made about the method of calculation of moisture content is important. However, in this context ( cut wood fuel,) you need to think about 'total' moisture content: ie wet weight divided by dry weight. Your moisture meter is calibrated to give a 'total' moisture content reading: it can't distinguish between what we call 'available moisture' and 'hygroscopic moisture' and this is not important as far as wood fuel goes 7. For firewood, info on ambient temperature (a.t.) or relative humidity ( r.h.) is not helpful. So I would not recommend using a multi -functional meter. Although, knowing the background r.h. of an indoor wood storage area might be useful, its not difficult to work it out by measuring the m.c of a piece of timber that has reached moisture equilibrium with its surroundings. Timber is a good 'barometer' of r.h. and some simple instruments actually use a piece of beech as the means of measuring r.h. fluctuation 8 finally and importantly.... electronic meters with prongs are measuring electrical current flow..they dont know if its flowing through wood, water, or metal! you have to figure that one out. You will get false (high) readings where salt is present ..so avoid measuring stuff in ground contact since mineral salts may be present. Carbon will always reads 'high', so dont measure burnt stuff. Heat affects the readings. A 2 deg C increase in temperature of the material will increase the m.c. reading by about 0.5% m.c. on most meters. So if you measure something that's say 50 deg C above the norm, you will find a huge inaccuracy in the reading, whilst the m.c. may have remained constant. You cant really get false ' low' readings from these meters unless your battery is dead! Hope that helps.

Ugh! Nasty case of haemerrhoids?

That's a good video. Your commentary is informed and pertinent. Many thanks for posting it..more like that please!

Sorry for the delay peeps.. Yes Peanuts it was.. I never did get round to setting fire to Charlie Brown though!

Well to be honest n the cold light of day there are some holes in my initial proposal...However, that's pretty much the method I remember using in a school lab experiment to determine CV of foodstuffs......we had to come up with a method and apply it to measure relative difference between refined sugar, cheese ( can't remember the type, but lets pretend it was Wensleydale just for the effect!) bread, and peanuts. Anyone guess which had the highest value? It was over 35 yrs ago; well before www so understanding how to design an experiment was all about 'doing it'.

I've heard Al Quaeda are planting forests of the stuff..Suicide Arborism! whatever next?

Tom...you any relation to 'Old Tom'? (see thread on selling by weight or volume). They're dissin him mate..think you might need to avenge the family name!

Ho ho Albedo...very good! Backandpack may be interested in the paper you've cited from or maybe that's rubbish too! Alternatively, calorific value could be measured DIY style. Easy to show relative differences but more difficult to measure absolute values because lab facilities would be necessary. Wood would be preconditioned to consant moisture content (sorry but it is crucial) uniform size and shape of particles of a known mass and heated in a sealed vessel to above its combustion temp. The combustion products (gas) given off is burnt in a controlled flame the temperature of which is pretty easy to measure. Temperature of flame x total burn time = calorific value. Repeat many times for a wood type/species and you end up with a statistically significant value ..well its the place Id start if I had to re-invent the wheel..but think its probably a lot quicker to read what's been done in the past!

Well; in a moment of self indulgence last night I splashed out on a top the range ART Ropeguide from Gustharts webshop... Will report thoughts on use when I get round to it

Albedo's point "Here the values for willow and pop are almost the same by species, but there is a difference of 8- 10 thousand kJ/kg between the younger and the older trees. Does this mean that younger coppice wood could be better firewood than older arb arrisings for example?" well I must say...that is interesting.. I must read that paper and then maybe some eating of my own words might be in order! ... but its Friday night and I'm going for a pint: deserved or not

Ropeguide it is then. Looks like Im finally going to have to drop the prusik! thanks again for all the useful opinion. cheers

Peter Raffle Sponsor ( interesting surname that..I see there are a few of you around) seams to be the last man standing who can see the wood for the trees. HaHa sorry. Come on BackandPack: you'll be trying to tell us 'work it out with logs' next ( OK maybe the pun is too old-school to make it as a joke these days? Belies my age). Wooww! I just had that Eureka moment Backandpack! Yes you and Archimedes are right...there is a logarithmic relationship between timber moisture content and exothermic energy of combustion...oh well maybe not..its just a bar of soap in the bathwater after all Interesting thread though Firewoodman. Thanks for that and to Peter R-S and Marko for staying sane..oh and correct as well!

Hi Firewoodman, how do you accurately measure the volume for delivery? Unless you have some special Welsh magic?! I'll stick to my previous view which t'other Peter has also made above. I agree with you about the variability of moisture content in any batch of timber. The way this is addressed is to measure many samples throughout the batch. That way a statistically significant estimate can be accurately made. The more samples tested and the wider their distribution, the more accurate your estimate will be. This is what hand held moisture meters were made for. In split logs I can estimate a few m3 in less than 2 mins with a simple moisture meter. The readings need to be from below the surface of each piece of timber ( best place is equidistant from the core and the outside or the piece and not too close to end grain ). With baulks or cordwood a similar method is used. I use a 6 mm diam probe on a moisture meter and drill 8 mm holes up to 300 mm long to quickly obtain useful readings to larger sections. On the matter of overhead costs: I take your point, but its dead easy to rig up a balance scales using known weights. Again you don’t have to weigh the entire load if you use a logical and statistically valid sampling method. If the method is sound and if it’s simple it can be safely duplicated. Provided you clearly state your methods for estimating, you shouldn’t get into trouble from Trading Standards Officers. If you can provide accurately valued firewood, then it will carry a preimum if you have the market for it. As you might have guessed, I measure material moisture content in materials as part of my job! Anorak or what!

Oh ok I'll check that one out bob. Cheers

I hate to be a pedant...well ok so no I dont.. but.. are my eyes deceiving me or are you really mixing mass with volume again? This is bound to confuse. The matter is quite simple. If people want to know how much they are paying for the energy they buy then they shoud buy solid flues such as wood by weight ( as you would with coal) and at a known moisture content. Where's the difuculty in that? Its far easier to measure the weight of a load of firewood than to estimate its volume (becausing of bulking ratios) and, with a hand-held moisture meter and a few minutes you can acurately estimate the total moisture content of the load ( I reckon on + - 5% accuracy). Subtract that from the load weight and you have the 'dry wood' mass (weight). From that you can estimate calorific value from published data and the now know dry biomass. Its not rocket sceince and if folk wished it, they could buy or sell in theoretical units of 'dry wood' or even potential 'thermal units' regardless of moisture content or deceptive bulking ratios.

Do you use a cuttable link in that chain; in case you are disabled and need to be rescued? cheers PB

Yes. Agreed; that is all other thing being equall..eg surface area to mass ratios. Oh and dont forget moisture content...or did I mention that! ..ho ho

Actually wasnt thinking of the ropeguide; more spiderjack or similar. However, there appears to be an overwhelling vote for ropeguide out there. Many thanks for all the opinions

Many thanks for the advice.

True Carlos Too true! Cheers

Does anyone have experience using ART gear. Looks cool to me but priceeeey! ? Informed views appreiciated Cheers

I think Educated Arborist has perhaps misread or misunderstood previous statements. I am in agreement with all Marko has previously stated. A summary of Marko and my own comments in this thread could be ' not much difference in calorific value at all: its all about moisture content'. Furthermore, I clearly used m/m ( or w/w) % being the accepted method of expressing moisture content rather than volume as did Marko. Similarly, calorific values are conventional expressed relative to mass and not to volume. Volumetric percentage of moisture content or calorific value are only useful when dealing with materials of a consistent or predicable density. Firewood aint like that! so where's the confusion Ed Arb? Also, if you have ever measured moisture content, you would appreciate that it is easy to measure the mass of a sample but much more difficult to measure volume because the later would in this context also need to be qualified by density: electronic moisture meters are calibrated to provide a m/m percentage m.c not a volumetric percentage m.c.. There is a substantial body of long-published and pretty authoritative literature by material scientist on this matter and I doubt that there can be much to gain from research other than informing oneself of the known facts; such as the importance of the exponential relationship between moisture content ( however it is expressed ) and heat output: 001_smile:

A couple of previous posts have correctly pointed out that mass for mass and at the same moisture content calorific value varies very little so it’s not worth bothering about. What matters most is moisture content. There is an exponential relationship between heat output and moisture content. So it is by far and away the biggest issue. In my experience, this fact is lost on many smaller suppliers and domestic purchasers. Do you guys use electronic moisture meters? I know a fair bit about em as have used many different types for over 25 yrs; so if any advice is needed I’m happy to pass it on. If you don’t want to acquire a moisture meter, then you can just use the facilities in the average kitchen to determine moisture content (takes longer though!).

Interesting thread guys. Some good points; especially those made by Pete. If you pressure and succeed in a quest for the mandatory certification of all individuals to splice (that is, for all splicing where PPE is involved) acquisition of this craft skill will become even more limited. More importantly, the more we rely on 'paperwork' to manage hazard ( e.g. CE certification etc.) the more rapidly the skill and ability to personally and competently assess risk and manage hazard will be eroded. Ultimately, this will result in fewer people with the 'competence' to manage hazard. Played out to its logical conclusions, we end up with a reliance on machines and machinery. Not an attractive or particularly sustainable outcome