Can you estimate this with an ordinary multimeter? If so, what sort of figures would indicate a moisture level below 20%?
I assume meters made for the purpose just measure resistance across a fixed distance, but I could be wrong.
Tim
In short No!
A DMM cannot even measure damp accurately, there are too many variables.
Density is your best bet.
weigh a fresh log, measure it, plane it or cut it to increase the surface area, stick it in a microwave on defrost for a few hours, weighing it until there is no significant reduction in reading.
Now you can do things by the ton if you wish using a winch and an FIBC, or if you want to get really technical go for the ureka thing on bathnight. Having got your start weight, just bide your time and weigh again in about two years if it's logs for a fire.
Tip! If married the FIBC approach is desireable. If Married and bath night is a "social occasion" then the FIBC approach is mandatory
AB
Nope, it varies too much with the type of wood and what you do with the probes.
If so, what sort of
No, because it varies so much with the wood and it isnt just the distance that matters
"Proper" moisture meters are just guessing, sometimes wildly. Take a representative bit of your firewood, weigh it accurately and stick it in an oven on low heat for a few days then weigh it again (after it has cooled). The difference is how much moisture it's lost (it probably won't be completely dry, but it will be mostly, probably).
You could try measuring resistance before and after drying to give some indication, but it probably won't be very repeatable - apart from anything else you're only measuring the surface, unless you want to chop it into 10mm cubes and measure the whole lot in each three directions ...
Do you re-read your drivel?
"Weigh it accurately" "Probably completely dry"
The number of clowns posting to theis NG when they haven't a clue never fails to amaze me.
Resistance means nothing. Forget it as far as wood goes.
Oven drying isn't linear. "Probably wont be completely dry" is an uncertainty that can be removed for all practical purposes.
To dry wood to the point where you have a "dry datum" needs a bit of certainty and it is readily achieved by increasing the surface area. Even then an assumption has to be made that the rest of the wood was of the same type, cut at the same time etc. But at least the representative sample has been verified. To verify the sample needs a number of measurements ideally, being a natural event the moisture loss will be exponential.
AB
There are probably tables to be found somehere that tell one the relationship between density of wood and its moisture content. It would be different for different species of course.
Also probably differs for timber grown in different places and/or at different times.
Well yes, you eliminate possible error where you can, but accept that some things aren't absolute and take account of that.
Yes, but not wildly I shouldn't think. We're only talking about "dry enough to burn" here.
Easy to do it right if you are going to embark on the procedure.
From personal experience misjudgement of when wood was dry enough to burn just relieved me of 2,300 Euro
It was a lot of wood and it wasn't much over a year old, so I have only one person to blame :-(
AB
However you only need to keep it for a while and then it's OK to burn.
Pretty much. Make upa jig to hold the DMM probes a fixed distance apart and measure a few logs that have been inside next to the stove (that's been on or in a room that is heated) for a few weeks. They'll be "dry". Compare those numbers with the numbers you get from logs in the outdoor log store. You'll get a "feel" for what is "dry" and what is "not so dry", which is all a "firewood moisture meter" in effect does.
Why does it matter? I have a wood heater and it does not matter how wet the wood is once you have started the fire, It dries out quickly.
Do not a lot of them actually need a specific contact area as well or even a probe that one inserts into the substance? Brian
'cause it takes lot of energy to vapourise water. Energy (heat) that goes straight up the chimney entrained in the the water vapour.
Maybe, but environmental legislation is on it way to control the burning of damp wood.
Chris
AIUI the simple two-pronged 'moisture' meters just measure resistance between the prongs, and then give a read-out approximating to the moisture content. Hardly a precise figure, as it will depend on the type of wood, it's conductivity, and the contact resistance of the probes. AIUI to get around that last, a three-probe meter should be used (but don't ask me why or how it works). The same uncertainties arise when measuring the moisture content of walls.
If you really want to know the moisture content of a piece of wood, weigh it wet, dry it to constant weight at 110°C and calculate the moisture content, deciding whether you want that on a wet-weight or dry-weight basis. But that only tells you the moisture content of that piece, of course. The bit next to it will probably be different.
If it's just for burning on a log fire, just heft it. That will tell you if it's 'wet' or 'dry', and be quite good enough.
Legislating for something that is difficult to measure easily is going to be interesting.
John
Reduced heat output and increases creosote/tar deposition in your chimney. Not always easy to sweep out. ?Less than 20% moisture? seems to be a pretty universal recommendation for all wood burners.
Tim
Indeed, Its virtua signalling boloocks.
You can walk around towns these days and smell coal buring in open fires.
Bugger the clean air act.
Renewable taxation has made it cost effective.
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