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

On Sat, 17 Nov 2007 12:14:19 -0800 (PST), robgraham
wrote:

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 ?

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?

;-)

--
Frank Erskine

On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

On 17 Nov, 23:26, "Brian G" wrote:
wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

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

In message , Brian G
writes
wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

Which will dry out quite quickly beside the stove

or when you put them in to burn

Did people have moisture meters 100 years ago ?

I don't think so ...

did they manage to keep fires alight ?

OP - stop willywanking and move on

--
geoff

robgraham wrote:
On 17 Nov, 23:26, "Brian G" wrote:
wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

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.

Rob,

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.

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.

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

In message
,
robgraham writes
On 17 Nov, 23:26, "Brian G" wrote:
wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

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 presume you mean "wasn't dry enough"

So it was blocked by water vapour ?


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.

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


--
geoff

In message , geoff
writes

A lot of trouble to go to though just to set fire to the logs!

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 presume you mean "wasn't dry enough"

So it was blocked by water vapour ?


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.

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

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



--
Tim Lamb

Tim Lamb wrote:
In message , geoff writes

A lot of trouble to go to though just to set fire to the logs!

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 presume you mean "wasn't dry enough"

So it was blocked by water vapour ?


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.

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

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.

Double skinned insulated ones are de jure these days for this reason.


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.

same for all wood, Not just elm.

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

The Natural Philosopher wrote in
:
OK
Tim Lamb wrote:
In message , geoff

writes

A lot of trouble to go to though just to set fire to the
logs!

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 presume you mean "wasn't dry enough"

So it was blocked by water vapour ?


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.

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

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.

Double skinned insulated ones are de jure these days for
this reason.


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.

same for all wood, Not just elm.

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

On 17 Nov, 23:43, geoff wrote:
In message , Brian G
writes

wrote:
On 17 Nov, 20:14, robgraham wrote:
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

You can get a nasty resistance meter for about £10 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

A lot of trouble to go to though just to set fire to the logs!

Which will dry out quite quickly beside the stove

or when you put them in to burn

Did people have moisture meters 100 years ago ?

I don't think so ...

did they manage to keep fires alight ?

OP - stop willywanking and move on

--
geoff

That's a bit unfair, Geoff. If you get a a blocked flue and the
professional tells you it might be because you've used damp wood, what
would you do ? Is some sort of device to help you get it right not
worth investigating ? I don't want another £500 bill for opening the
flue up and removing sack loads of soot.

Exploring the use of a moisture meter is perfectly reasonable under
the circumstances. As for not having such an instrument in the past,
their flues were a dam site larger than ours today, so that statement
is equally stupid.

And it is quite clear from AJH's comprehensive and knowledgeable input
that just putting a log beside the stove is not going to dry it out in
the short term either.

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.

Rob

In message , AJH
writes

The simplest judge for whether hardwoods have fallen below 30% mc wwb
is to see if you can blow down the grain.

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
--
Tim Lamb

In message
,
robgraham writes

That's a bit unfair, Geoff. If you get a a blocked flue and the
professional tells you it might be because you've used damp wood, what
would you do ? Is some sort of device to help you get it right not
worth investigating ?

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

I don't want another £500 bill for opening the
flue up and removing sack loads of soot.

As someone else said, you really should be getting a chimney swept
annually


Exploring the use of a moisture meter is perfectly reasonable under
the circumstances. As for not having such an instrument in the past,
their flues were a dam site larger than ours today, so that statement
is equally stupid.

And it is quite clear from AJH's comprehensive and knowledgeable input
that just putting a log beside the stove is not going to dry it out in
the short term either.

No, it takes months, which is why you should split / prepare in good
time and stack them
--
geoff

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.....

regards
--
Tim Lamb

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

--
geoff

On Nov 18, 9:35 pm, robgraham wrote:
If you get a a blocked flue and the
professional tells you it might be because you've used damp wood, what
would you do ? Is some sort of device to help you get it right not
worth investigating ? I don't want another £500 bill for opening the
flue up and removing sack loads of soot.

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.

Exploring the use of a moisture meter is perfectly reasonable under
the circumstances. As for not having such an instrument in the past,
their flues were a dam site larger than ours today, so that statement
is equally stupid.

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.

On 18 Nov, 22:15, geoff wrote:
In message
,
robgraham writes



That's a bit unfair, Geoff. If you get a a blocked flue and the
professional tells you it might be because you've used damp wood, what
would you do ? Is some sort of device to help you get it right not
worth investigating ?

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

I don't want another £500 bill for opening the
flue up and removing sack loads of soot.

As someone else said, you really should be getting a chimney swept
annually

Exploring the use of a moisture meter is perfectly reasonable under
the circumstances. As for not having such an instrument in the past,
their flues were a dam site larger than ours today, so that statement
is equally stupid.

And it is quite clear from AJH's comprehensive and knowledgeable input
that just putting a log beside the stove is not going to dry it out in
the short term either.

No, it takes months, which is why you should split / prepare in good
time and stack them
--
geoff

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

In message
,
robgraham writes
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 seemed to be moaning about the fact that it had to be done at all

- you just assumed it and issued me with an
instruction to do so.

No, someone else said that, I pointed out that they had


How do you know that I don't split and stack in good time

I didn't I just said that's how it should be done


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.

Well, I've given my opinion and the reasons behind them

If you're too precious to take it on board without sulking like a kid,
that's your problem, not mine


--
geoff

On 18 Nov, 11:34, AJH wrote:
On Sun, 18 Nov 2007 09:45:09 +0000, Tim Lamb
wrote:

There is an expert in here somewhere.....AJH?

Idontdoexpert!



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.

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.



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.

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.



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.

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

Dear AJH
Impressive... general chemist or specialist wood chemistry?
re
*******
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??
*******

Twin probe ones are, indeed, resistance meters. (There are also
capacitance and radio wave ones.) I suspect that you will be
measuring the resistance of the wood structure mainly cellulose Beta
1:4 linked glucose 2000 units long - with the not disimilar
hemicellulose which when there is no water in the wood (105 C for 48
hrs) would be high and when there is lots of water both in the wall
and the lumen then you will get conductivity. I imagine that the meter
is thus inverted so that it gives a "high" reading when resistance is
low.
What actually causes a reduction in resistance would I suspect be
salts in the water rather than the wood but you may be right.
Chris

In message , AJH
writes
On Sun, 18 Nov 2007 21:38:01 +0000, Tim Lamb
wrote:

In message , AJH
writes

The simplest judge for whether hardwoods have fallen below 30% mc wwb
is to see if you can blow down the grain.

You are going to have to explain this:-)

If the log is has dried to 30% there will be no water in the vessels,
so it will pass air and you can tell this by putting it to your mouth
(sealing with lips) and blowing.

Ah! Thank you.

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.

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.

Defects? This is meadow land timber with who knows how many generations
of farmers fencing staples buried. The intention is to provide enough
material to build the framing for a 20'x 40' single storey barn. At
present, I have 4 lengths of Oak trunk 10' long by 3' dia. I can get
another 20' without bothering the forestry commission.

You will have to translate *Hft*. Forestry acronyms are less
understandable than most. What is a board foot for example?

regards

--
Tim Lamb

wrote:
On 18 Nov, 11:34, AJH wrote:
On Sun, 18 Nov 2007 09:45:09 +0000, Tim Lamb
wrote:

There is an expert in here somewhere.....AJH?
Idontdoexpert!



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.
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.



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.
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.



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.
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

Dear AJH
Impressive... general chemist or specialist wood chemistry?
re
*******
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??
*******

Twin probe ones are, indeed, resistance meters. (There are also
capacitance and radio wave ones.) I suspect that you will be
measuring the resistance of the wood structure mainly cellulose Beta
1:4 linked glucose 2000 units long - with the not disimilar
hemicellulose which when there is no water in the wood (105 C for 48
hrs) would be high and when there is lots of water both in the wall
and the lumen then you will get conductivity. I imagine that the meter
is thus inverted so that it gives a "high" reading when resistance is
low.
What actually causes a reduction in resistance would I suspect be
salts in the water rather than the wood but you may be right.
Chris



As has been said, the moisture level on the surface is no guide at all,
and the prongs on the cheap meters won't penetrate without breaking. The
ones they use in sawmills are hammered into the logs, and are built
accordingly.
The only way to get accuracy with a cheap model is to crosscut a 6" or
so length of log, then split it down the middle, then immediately test
the faces.
This doesn't take the resin content into account, which I would guess is
what's causing the original problem, and drying doesn't remove that. In
kiln dried timber you can often see it bleeding from the end grain.

In message , Stuart Noble
writes

As has been said, the moisture level on the surface is no guide at all,
and the prongs on the cheap meters won't penetrate without breaking.

ifankewe


--
geoff

In message , AJH
writes
On Mon, 19 Nov 2007 10:55:28 +0000, Tim Lamb
wrote:

You will have to translate *Hft*.

Hoppus foot, the traditional way of measuring hardwoods, 27.736 per
m^3 IIRC. It's a round measure that aims to indicate how much sawn
wood the log will yield.

Ah. So if I divide your 150Hft guess by 27 I get an answer in cubic m of
round wood? OK.

Forestry acronyms are less
understandable than most. What is a board foot for example?

merkinism

12" x 12" x 1"

Defects include knots, inclusions, shakes ( laminar separation I
suppose), cross and spiral grain.

All of those but this is eye candy construction with the roof load
carried elsewhere.

regards
--
Tim Lamb