openspaceman

Is that by weight or meter?

I've never been back to see how it fared but I found the cement did make a bond through the hessian, albeit I'll grant it was probably not a good one. If it's deep remember to leave some gaps for weep holes else hydrostatic pressure can push the wall out.

Yes because the relative humidity of the air in the oven is very low, so it has lots of capacity for absorbing more moisture from the log plus the heat delivered into the log vaporises the water so it comes out as steam. In the winter the RH is high but that's because the air hasn't much water capacity and being cold water shouldn't migrate into the wood as fast, but we'll see.

Will you weigh it every week or so? My guess is it will reabsorb moisture slower than it lost it as temperatures are lower for the moisture to migrate but will be interested to see.

This is largely because you exposed more fuel surface area as well as increasing the air supply. Sending flue gas up the chimney at 340C seems a bit wasteful Softwoods tend to have more calories for the same weight but also, along with any less dense wood) the surface heats up quicker so they ignite more easily.

Yes didn't the boiler form part of the combustion chamber?

Yes and as Stubby says this is one of the techniques a modern stove uses, essentially you move the heat exchange surfaces till after the combustion is completed, so they don't quench the secondary flame.

Yes but you need to see this is not the full story. If you burn wood at 50% mc wwb the energy cost of the water is only 14% of the available energy but we all know burning wood this wet is difficult because the fire never gets up to temperature and the flue gases are so cold that water and associated tars condense in the chimney and run back down. The thing to realise is that the energy in the wood all ends up in the combustion products which then lose heat through the stove walls before they are vented. If the wood is wet then with any given stove the temperature may not get high enough to burn the wood cleanly. It looks like you need secondary combustion temperatures of around 800C to burn wood cleanly and there may not be enough energy in the wood to maintain this temperature if the firebox is not well insulated. Also small stoves have more heat loss for their volume than big ones. Which is why big industrial burners with refractory linings and some pre heated combustion air can burn whole tree chip at 45% mc but my little Jotul cannot.

Bur even that is misleading because we seldom sell split logs by tonnage (although you may well by roundwood for converting by the tonne. So take your tonne of timber at 25%mc wwb and 3700kWh/tonne, it contains .75 tonne of oven dry wood which has a calorific value of about 3975kWh, season it to 15% mc and it now weighs 0.88 tonnes but has the same calorific value. Burn the batch at 25% mc and you yield about 3700 (I make it 3787)kWh Burn the same batch at 15% and I make that 3862 kWh

Yes I should have said dense refractory bricks.

I agree but there are a couple of points, even with a fast hot burn the rate of evolution of pyrolysis offgas will not be steady with bone dry wood. You cannot keep bone dry wood that dry, even pellets start disintegrating in a damp garage If you supply enough secondary air for the worst case you end up sending too much heat up the flue most of the time, this is insignificant on the domestic scale but not so on a commercial scale , which is why they use wide band oxygen sensors in the flue in order to supply just the right amount of air. NOX was mentioned in a recent reply, perceived wisdom is that NOX forms above about 1500C at ambient pressure, the flame temperature of wood is only around 1600C (or else you could smelt iron with wood rather than charcoal) and by the time you add above 50% excess air to ensure a clean burn you will be below that. I'm all for burning dry wood and 20% mc is good and easily attainable in this climate under cover but as long as you can get up to temperature is the real condition for clean burning and a stove with an insulated fire chamber will manage this where a metal box won't. My Jotul is essentially a metal box.

Old night storage heaters were a source of dense firebricks. Yes sand was used to fill old back boilers but I always wondered what happened when the steel burned through.

3. If enough stolen gear gets registered AND people get to check stuff before they buy second-hand it will reduce the market for stolen gear Thieves only nick what they can sell on

Firstly consider the other fuels we burn, with petrol we meter in just about the right amount of fuel for the air present in an engine, with diesel we inject a measured amount of fuel into excess air. With a gas flame we use the gas passing through a nozzle to entrain just the right amount of air to burn cleanly. Similarly with a pellet burner we trickle a few pellets in at a time that on average the conditions in the burn pot remain the same and air supplied to burn the pellets but wood is a bit different from the other fuels as it doesn't burn directly but in two stages (actually diesel in an engine burns in two stages also). The primary stage is when wood is heated to pyrolysis temperature and evolves gases and vapours. The heat from this comes from burning charge that has already been formed and this char ignites at a relatively low temperature, about 250C. The pyrolysis products and products from burning the char then rise as gases and vapours where they burn in the secondary flame. Conventional fires aim for the air to the primary combustion to control the power by restricting the air supply to the bottom of the combustion, the evolved offgas then entraining sufficient secondary air to burn these products completely. Unless air is well mixed into the gases from the primary combustion the oxygen must combine with the gases at the flame surface, if the dwell time in the flame is insufficient or there is not enough air Products of Incomplete Combustion (sooty particles) form. Something like 70% of the heat from wood comes from burning in the flame and 30% from burning out the char which is why it is important to maintain a flame and not let logs smoulder. In the log stove we have a major difference from when fuel is metered in in that a whole batch of fuel is in the firebox at once. So not only are the outsides of the log burning but also the interferon of the log is heating up. As I said pyrolysis of the log is initiated by the is heat at about 270C and is mildly exothermic, which means it produces a little of its own heat without needing further input from the fire below. During pyrolysis all the gases are released from the log but if the fire is turned down low there may not be enough secondary air to burn them, hence soot is formed. So a very dry log can heat up and evolve a lot more gas than the fire can provide air for. However to evapourate water needs 2.3MJ /kg which is hundreds of times more heat than is necessary to raise dry wood to its pyrolysis temperature. So the small amount of moisture in the wood slows down the heating up of the interior and the wood progressively burns from the outside inward, releasing offgas in a more regular manner You can demonstrate the concept by taking a green log and splitting it in half, dry one half in the oven. Then put them both in a fire, you will see the oven dry log quickly evolves gases which ignite, shielding the log, then when the pyrolysis is complete the charcoal then turns grey as it burns and ash is exposed. The wet log steams for a while and then the outside chars, this char is burn as it is exposed and the log burns away to ash from the outside till nothing is left.

You can store photos and at work I used to write the firm's initials with a soldering iron on the plastic parts if they came into the workshop.

My theory is a bit complicated to explain but if you consider the "smoke" created by the heated log is in fact gases and vapours from the pyrolysis which then has an inadequate supply of air OR becomes too cold to burn out completely then that forms the products of incomplete combustion which are smoke. Smoke is an aerosol of soot and condensate droplets so if there is a lot it appears white (as does milk) or if less it looks blue because of the way the droplets/particulates split the light (which presumably why the sky is blue) I can attempt to explain my theory how a little moisture might modify the burn to avoid the sudden evolution of this offgas should you wish.

Shame I have nowhere to put it, it would keep me warm two ways

...but there's the arbsafe service on here where you can store all that info and flag it as stolen if necessary. Everyone on here has then got access to see stolen items or type a serial number of a saw they are offered or repairing to check. It needs a big database before it becomes effective There's no charge at present

Well if that's an indication of the validity of the rest of the article... In fact the figure I was told was 12% and my guess this is for logs as there may be a reason for this. Particulates from wood burning are a product of the secondary flame and there is little doubt they are in the PM2.5 size class (worst for lung retention) but a good hot secondary flame should prevent most of them from forming. I've been thinking of monitoring the air downwind of my chimney except I'm next to a fairly busy road and the monitor costs £220/week plus delivery plus insurance plus VAT

I don't know, shouldn't hurt for a short test but don't let the pump run dry. Why not run it with the thermostat out whilst stationary and see if bottom hose gets warm. Don't run on the road without a thermostat as engines need to be warm to run efficiently. New thermostat will be about £20

Old fashioned bellows ones failed open, waxstats tend to fail closed. The heater circuit is open when the thermostat is closed so the heater works. I cannot understand the bottom hose being cold if the thermostat is open.

I thought the first couple showed bonfire damage but one of the later ones looked like ash dieback. We seem unanimous that it's not worthy of retention.

Are you lot planning on casualties or are they useful for anything else?

I was chatting to a young driver of a new Komatsu 15 tonnish forwarder on Sunday, His ruts were deeper than my County would travel and was getting about 100 tonnes out on a site I would have managed 70 tonne but I would have been miserable, frozen and wet some 10 years back. His cab was air conditioned and he could listen to the radio but the rub was he has to have a digger tidy up behind him on every site so cannot contemplate jobs less than 1500 tonnes. There were two forwarders and a harvester on site, probably nearly as much money invested as the cost of the two cottages they were parked by. I'd love to know the comparative costs now compared with taking it more slowly with motor manual, I'm sure it is more economic but the cost to the woodland...

I spoke with him yesterday and I had got it wrong, the local dealer replaced the motor with one from the original importer.