Well done, Marcel. It would really help if we stuck to the botanical names for the trees we use in a discussion like this. All I have to do now is find my tree book, which is somewhere next to the insect book, under the....
I guess my reluctance about fir stems from the care I take with my fireplace flue; it's always been a mantra with me not to burn resinous woods in the fireplace, because the flue temp never really gets all that high, unlike my wood stove. And, I've seen exploding bits jump the screen onto the pine floor. You're probably right about creosote burning off in the bake ovens we use because of the exceedingly high temperatures. Even so, I try to avoid using it.
Regarding log length: The deck of my AS bread oven is four feet deep by three wide. I begin with a smallish pryamidal fire of mixed hardwood and softwood (short bits, split bits, branches, offcuts from my woodshop), which I light with a propane torch. To make sure there's enough air under this initial fire, I commonly use a piece of 2x4 on edge, front to back, to stack it on. Then, I add a few longer pieces of branch wood, front to back. When this is burning well, I put on several long split pieces of pine or other softwood that reach all the way to the back wall of the oven, then, after the pine has caught, enough hardwood (same approximate length) to almost fill the chamber. Split wood has more surface exposure than wood in the round, so it catches faster and burns better to ash. Having said that, though, my ideal piece of wood is a standing dead maple limb about 3 inches in diameter and around four feet long. I suspect limb wood in the round would be best for a pizza oven, because it tends to burn into dense, long-lasting coals that you can push aside when you bake.
The main point is to get the fire to burn, as David Wing and Alan Scott say in
The Bread Builders, "as a wall of flame from the front all the way to the back," so long pieces work best for me and I don't have to mess with the fire as much. Also, you want the heat constantly and evenly distributed from the front to the back of the dome and hearth. But, of course, I'm dealing with a rectangular bread oven of some size, and I rake and brush the oven clean before baking.
In practice, the logs I split are kept to 46", so the ones in the middle don't come too close to the oven door and shoot flame up the chimney or incinerate my draft control door. When the completed fire is burning brightly, after about half an hour or so, I fit the draft control door to really get it burning. All this is approximate right now, because it's very winterish here
(-15C this morning), and dry, cold draft air seems to have a tremendous effect on how the fire burns and how much wood is needed. Thus far, it has taken two complete burns to bring my high mass oven up to heat (dome: 650F, hearth: 750F before resting to even out the brick temps for an air temp of about 550F, depending on what I'm baking; higher for baguette), but that will probably change as the weather moderates. This is nothing like using an indoor woodstove, where conditions are much more controlled and the inside draft air is warmer and perhaps more humid at first. I combine an oven air temperature gauge with readings from the four themocouples I installed to work out the temps.
I now have two separate woodsheds: one is for indoor fireplace and woodstove fuel (cut to approx. 16"), the second is strictly for the oven, and it measures 4 feet deep by 22 feet long by 8 feet high. I'll try to post some pics later today. As a side note, I'm taking my photographs at the lowest resolution the camera will allow, but the files are too large to post here. Just have to figure out how to reduce them.
There is some variance between the recommendations for wood types in
The Bread Builders and Alan Scott's own plan book, but this probably has to do with the differing dates of writing, editing and publication, plus species availability in different locations---recommendations on hardwoods versus semi-hardwoods versus softwoods, that is. It appears from photographs that Alan Scott himself burns a lot of eucalyptus (in the myrtle family) that was imported into California from Australia and has spread everywhere on the central CA coast. I've turned some on the lathe, and would call it a semi-hardwood (although it's a type of pine) and quite oily. Others there (Tim Decker, for example, pictured at the end of
The Bread Baker's Apprentice) use Live Oak, a hardwood much beloved by Acorn Woodpeckers.
Alan Scott recommends a "bright" fire, meaning lots of flame, I take it. But I've found it all really comes down to BTUs, PLUS brightness, PLUS the air temp and humidity outside the oven. If I can get it and it's well seasoned, hardwood gives the best heat per pound of wood, but softwood burns the brightest, so I mix the two. As you might expect, semi-harwood is in the middle, you just need a bit more of it than hardwood. I'm finding that this mixed method works best--for now, at least.
You're absolutely correct, Marcel, you want the oven white hot, meaning all the soot has burned off. In my experience, this won't happen, or at least not as quickly or reliably, with wood that isn't well seasoned. You can even drop the temperature you have already achieved by adding green wood.
David should look into the botanical names for the trees he'll be using in Florida. There are many, many types of mahogany, and they range from hard, oily and dense (South American) to soft, dry and open grained (the wood used for "mahogany" baseboards, door trim, etc. Asian?). I'm familiar with the gumbo limbo from around Fort Myers and Sanibel Island. I don't know what its burning characteristics are, but you might try tying up bundles of thinner branches, letting them dry and using them. The Australian Pine you mention is, I believe, related to eucalyptus, which is also defined as a type of Australian Pine. You've got quite a bit of it down there, it's semi-hard, so maybe zero in on it. But, because it is oily, it will likely have to cure one season if it's cut live. Standing dead is best. Citrus would work; it's usually semi-hard, but careful to cure it well or it won't burn brightly. By the way, when I'm talking about green wood, I'm referring to sap content, not necessarily water content. If dry wood gets rained on, it will dry fairly quickly when covered and well ventilated.
There are other avenues, of course. Most of the time, the pallets used to deliver brick, block, cement, etc. are made from oak because they must be strong. If you are up to the task of breaking them up and pulling the nails, they're quite dry (sap) and work very, very well (if so, to save your back and knuckles, invest in a long handled nail puller, not a claw hammer). Often, you can get pallets free from some companies that bring in a lot of materials to their warehouses (Home Depot?). Don't forget large scale woodworking shops. They have to get rid of their offcuts somehow, somewhere. To them, they're in the way, and you'll probably find a mix of hard and softwood. In cities, they probably have to pay for disposal. If you're not a wood afficianado, the heavier of two pieces of wood of the same approximate size will be the hardwood. Also, in cedar areas, there might be milling operations that generate a lot of slab wood with the bark on it. It's useless to them, so maybe strike a deal with one of them. An electric chainsaw or sabre saw would do nicely to cut cedar slab to length. Don't, please, use a circular saw. Way too dangerous because of kickback. As well, don't forget new housing developments. There's almost always a dumpster full of offcuts. It will be mainly spruce and likely wet (sap), but, hey, it's free, and it will get you started. Talk to the site supervisor. They normally have to pay per pound to get rid of it. Split anything wider than a 2x4. My general rule is not to burn anything painted, or anything with glue in it, like plywood, and nothing pressure treated.
Across the board
, I've found there's a great deal of uncertainty, not to say confusion, out there (both in books and on the web) regarding oven firing, firing times for different sorts of ovens, best wood types, curing, coking, brick temperatures, etc., etc. Maybe we might all think of coming up with some sort of collective document on these topics that would help us all out, whether we bake pizza or bread, small oven or large? My career has been highly varied, but I have written several and edited many, many books on many subjects, and I'd be willing to help out. The chapter I'm thinking of is called "The Scavenger's Apprentice." Just a thought
. I've been heating with wood a long time, but firing my brick oven is very different, so I'm still at the learning stage.
It's very cold here today, so I've had some time on my hands until it warms up and I can go split wood. This has been fun, and I hope it helps.
Jim