Building A Better Fire

[david s]

Re: Building A Better Fire

I once weighed my wood pile before and after firing and found it used 4kg of wood to clear the dome. This took one and a half hours and the thermometer situated halfway up the dome wall was showing 350C. The mass of the wood used is a better measure than volume as it is the weight that determines how much energy the wood contains.I should mention that my oven is only 540mm (21") diam. So the chamber volume is small. A 20% increase in diam means around a 70% increase in volume. Fuel consumption generally is directly related to chamber volume.

Regarding the amount of fuel in the chamber at any one time, it is better not to overload the chamber as this results in a rich atmosphere which is not so efficient. It's a bit like a car engine running on an over rich mixture. When firing kilns an over rich mixture is sometimes used for certain effects and is called a reducing atmosphere. When changing from an oxidation atmosphere to a reducing one the kiln usually stops rising in temperature and sometimes the temperature actually drops, although more fuel is going in. Attempting to control the atmosphere in a WFO is difficult because the gases from the fuel are released progressively, but it does mean that less is more and the loading of the fuel is somewhat counterintuitive. Too much fuel will not lead to a faster temperature rise or hotter fire.

[navyintel]

Re: Building A Better Fire

G'day
I saw your new/old tool, and I was taken by the shape. I thought different!, that shapes got me in. It's an old design, so does that serve a purpose, is it something developed to that shape over time? I was also struck by how shallow it was my own aluminium rake is twice as high and half as wide.
Decided at that time I was keeping an open mind to this design and see what you posted when you used it. So I'm still interested in how it proves in service. I'm not even going to hazard a quess.
Regards dave

Well, I tried it today and put an hour of fire in the oven. Sole purpose was to put the tool through it paces.

I found that the unusual shape has a specific purpose - since the offset is doubled over (the u-shaped portion) and thus has more than twice the weight as its offset - it counter balances the blade so the tool does not twist in your hands. Also, it adds weight to the end of the tool which helps hold it down when plowing through heavier ashes and coals.

I also found that the blade tip reaches into all corners of the oven and is reversible by flipping it over.

Some of the tools I make are one offs and never see use again in their current form. I love to experiment.

In this case I think I have a winner. I am posting a picture from the original plate from the 1730's - I hope that it is readable in it format and size.

Thank you Dave for your interest and comments. It helps alot

[cobblerdave]

Re: Building A Better Fire

G'day
I saw your new/old tool, and I was taken by the shape. I thought different!, that shapes got me in. It's an old design, so does that serve a purpose, is it something developed to that shape over time? I was also struck by how shallow it was my own aluminium rake is twice as high and half as wide.
Decided at that time I was keeping an open mind to this design and see what you posted when you used it. So I'm still interested in how it proves in service. I'm not even going to hazard a quess.
Regards dave

[navyintel]

Re: Building A Better Fire

For those reading about building a better fire, take a look at the tools forum and look at the "Rooker" that I built. I would appreciate comments on this as well. Not so many people are looking at the tools - I think they think it for tools to build you oven, and maybe it is. Oh well. I have not used it yet and I have not attached a handle to the second rooker that will be for close in work where a long handle will get in the way. Once I had all of the materials, it took be less than 1/2 to make the tool.

[cobblerdave]

Re: Building A Better Fire

I think the moderator vets postings by new users, so it took a little while to appear.
Talking about vets ..... oh .. doesn't matter ......

Gudday Wambat
Check out the Aust section, you have a fellow SA called dodgygrog just starting out same as yourself.
Regards dave

[Wambat]

Re: Building A Better Fire

I dont know why it took 2 days for it to show up in my mail.

I think the moderator vets postings by new users, so it took a little while to appear.
Talking about vets ..... oh .. doesn't matter ......

[navyintel]

Re: Building A Better Fire

Typo ??? Thought it would stink up the place....

Dog Fur that is

PS....
Sorry... my first post on this board....
And my really strange sense of humor

I found your post at last. It just popped up on my email and I could not find it in the thread - I thought you had used quick post and it went somewhere else. I dont know why it took 2 days for it to show up in my mail.

[navyintel]

Re: Building A Better Fire

To WOMBAT:

This your question-

What I use is Doug fir.
---End Quote---
Typo ??? Thought it would stink up the place....

Dog Fur that is

PS....
Sorry... my first post on this board....
And my really strange sense of humor

Try posting a reply instead of quick reply - that way everyone can see it and respond. I am no expert and when you post it online you get the benefit of the hundreds that are expert or have at least felt your pain.

Answer: Doug Fir is short for Douglas Fir. It is a medium soft wood that grows tall in the North American west. It is more dense than pine and does not have sap, It is the principle material used as building lumber. Most American homes that are "stick" (wood) constructed use Doug Fir as the structural material - you can find it common in (inches) 2x4 2x6 2x8 4x4 4x6 and 4x8.

It does does not have a bad smell but it is a little acrid. Not great for cooking. The BTU is less than oak but more than pine. Best size is a 2x4 split to 2x2 or smaller - around 18in long.

I use any non toxic wood I can find to heat the oven up. If I only had eucalyptus, I would use it gladly, very heavy and burns hot. I use it also.

[navyintel]

Re: Building A Better Fire

Apart from 42 being the answer to life, the universe, and everything, (proving that there is something fundamentally wrong with the universe, apologies to Douglas Adams), I don't quite get what you mean.

However, I believe cobblerdave uses palm fronds to heat his oven.
Apparently this is a free resource that would otherwise present a disposal problem.

It doesn't take a lot of wood to heat my 30 inch to white. One day I'll cut a wheelbarrow full of wood and see how much I have left after a decent pizza party.

I suggest it won't really take a lot of expensive wood to heat any oven.
The thing is, while I like to use low ash timber, I also find my oven heats better if I use thin sticks to get a nice raging fire going. This means I commonly find myself picking up the thin branches of redgum that the serious firewood collectors leave behind.

I re-read your post and you indicated that you get a "raging fire going." you might try a lower level fire. I use a fire that goes up no higher the 3/4 of the way up the wall.

I found that a bigger fire is not hotter, only more BTU's up the chimney. Try an experiment and use a fishing weight scale to weigh out your fuel in 5 kilo piles (type of fuel not relevent). Then build a smaller fire and let it burn longer. I find that 5 kilos takes about 20 min to consume as you gradually add fuel. This gives you time to sip a little more beer and even smoke a nice cigar while giving all the appearance of working.

It is my experience that since the fire is not hotter, than it is the amount of time the heat is exposed to the brick that gets a nice even hot oven.

[V-wiz]

Re: Building A Better Fire

Thanks ^ ill try it when im able to fire the oven

[V-wiz]

Re: Building A Better Fire

Gudday
I use the top down method and build my fire in the front of the oven and get it flaming and the chimney hot. It's a simple case of pushing it in to the middle of the oven and it will do its thing . Advantage I find is that it easy to build the fire in the front no reaching in. Heats the chimney so it draws well from the start. Recon there's less smoke as the fires pretty hot already when it arrives in the cold oven. I'd recommend you give it a try can't hurt.
Regards dave

Thanks Dave, ill give it a try

[navyintel]

Re: Building A Better Fire

Gudday
I use the top down method and build my fire in the front of the oven and get it flaming and the chimney hot. It's a simple case of pushing it in to the middle of the oven and it will do its thing . Advantage I find is that it easy to build the fire in the front no reaching in. Heats the chimney so it draws well from the start. Recon there's less smoke as the fires pretty hot already when it arrives in the cold oven. I'd recommend you give it a try can't hurt.
Regards dave

I agree with cobblerdave: It not only heats up the chimney which improves the draw, but it heats up the top lip of the oven door. When the lip is very hot the gasses in oven pass over the lip quicker - its almost as if it becomes slippery. The overall effect again is ease of fire build - Hot coal barrier at the door to eliminate cold air going in (like in Detroit -what -40f?) - Hot chimney and a hot door top. When you try it as described, let me know how it works - we can always adapt new methods.

[Greenman]

Re: Building A Better Fire

I use a variety of timber to get things going. Most of it is dense hardwood but being a 'harvester' I can tell you that mangrove displaced by the floods is good starting wood when it eventually dries out. Some of the eucalypt s are good for quick heat but the really dense timber like ironbark and the like are great to maintain temps when used as larger pieces.

I have a supply of timber from old well dried stumps and roots that is as heavy as lead and burns for a very long time.

The term 'scrounger' has been discussed on the forum before and when it comes to fuel for the forno, anything that has not been treated or doesn't emit anything nasty is good to go, including the well dried prunings from the garden. I am aware the the term means different things but in the sense of recycler it is good for me.

I am a bit lucky with being in the country rather than the city but even in the city there are opportunities for the keen scrounger. Storms bring down trees and branches and they need to be removed by someone, and if you have a chainsaw............

[cobblerdave]

Re: Building A Better Fire

Does anyone in Australia have some figures on how much hard wood it takes to get the oven sorted.
Im assuming 42 is the standard
but
Im willing to go smaller

Do people use a bit of wattle or palm fronds to get it started?
Im trying to do the maths on how much wood Im going to need everytime I fire one up.

Gudday
Recon Micks s about right with the small sticks and the 1/2 to 3/4 of a barrow of wood. Sticks burn fast and hot and give you good heat plus there's little or no chopping large logs into smaller bits.
As for burning wattle its an acacia and they have a high tannin content. Of course they burn but tend to produce a acrid smoke as long as you burn them at the beginning not the end when they might taint your food.
I burn the fallen palm fronds as well again the smokes not sweet. If there are not complete dry it doesn't matter they burst into flame instantly in a hot oven. They burn fast so its one at a time till there are gone.
There was a time that I didn't take out the excess ash but now I do as it can insulated the floor from the heat from the dome and active coals. It's a pain playing with hot ashes but it works out better.
Hope something here might help.
Regards dave

[cobblerdave]

Re: Building A Better Fire

Interesting idea, but may i ask why you guys build and start the fire at the entrance? In my case i build my fire inside at the middle, i put my blast door on for 30 second and everything is perfectly lit and smoke goes up the chimney without a problem.

Gudday
I use the top down method and build my fire in the front of the oven and get it flaming and the chimney hot. It's a simple case of pushing it in to the middle of the oven and it will do its thing . Advantage I find is that it easy to build the fire in the front no reaching in. Heats the chimney so it draws well from the start. Recon there's less smoke as the fires pretty hot already when it arrives in the cold oven. I'd recommend you give it a try can't hurt.
Regards dave