Backyard WFO number 2
So we are starting planning for a new house, with a hard requirement that it must include a backyard wood fired oven. This will be our second WFO, having just moved out of a house where we built a DIY kit version in 2009. We averaged 1 to 2 uses per fortnight, and are keen to continue.
The first oven, as mentioned, was a kit DIY build on a steel frame. The oven was a barrel vault design, with a hearth area of 700x920mm. The oven had only the one chamber, with the chimney rising from the high point of the chamber. The results were wonderful for pizza for a family, or a medium gathering, but we struggled with maintaining enough heat to do breads, or roasts and the like. In fact after a large, long burn the night before, it was already fully cool by morning.
This has led to us considering the options for our new oven. With our lessons learnt, we set about prioritising the requirements:
- Ability to bake full loaves of bread - if I can make a couple of loaves a week that are half as good as the Flute from Maison Drap in Lyon, I'll be happy :-)
- Ability to roast large meats/poultry without a need to enclose in a heavy pan
- Can do up to two pizzas at a time
- Can stay warm over night, so we can use it again in the morning for breakfast, or at worst require a small firing in the morning. Our ultimate goal would be to have one whole weekend (Friday night to Sunday night) where everything we eat comes from the oven
- Slightly smaller than the last oven - we never used the whole interior at one time.
Similarly, we worked out what wasn't important to us:
- Heat up time - 3--4 hours is not a concern
- Weight/portability etc...
Based on that, and the kind sharing by janij, we have settled on the 24x30" Alan Scott design. We've had the Bread Builders from before the first oven, and always thought this to be the pinnacle of what we had seen.
Does this make sense, or have we misjudged based on our needs?
and you have settled that question. Given your goals, and your list of things that matter (and don't), I like your plan. It makes perfect sense in my opinion, and it is what I would have suggested. Even having settled on an excellent (imho) plan in the Alan Scott though, there are a couple of things you should address, and both of these are insulation issues: Under the floor and around the oven.
The plans in The Bread Builders have been held by several critics I have read to be under-insulated, especially under the floor. This is easy to adjust for as long as you make the adjustments before you move any dirt or lay any brick. The same is said by some of the insulation around the oven barrel and cladding, above the floor level. This can be corrected easily as well, but everything works out best if you take it all into account from the beginning. These factors,along with the thickness of your heat storage masonry layers, have the biggest impact on how long the heat will stay in your oven. That, and remembering to put the door back on after that last bake, of course.
I decided to build my own oven (See mine here), and on most counts I am glad I did. I do still pine for an Alan Scott Masonry Oven, but I could not afford to have it done professionally, and I don't have the skills to do it myself. My biggest regret in my little mud oven, though, is: Not enough insulation under the floor. I could never expect my oven to be hot enough for anything the next morning. It just does not hold heat long enough. I hope you avoid that problem, at least.
A new oven... SO exciting. I hope you post some photos of your build so we can all keep up, and drool over your good fortune!
Use ceramic fiberboard and ceramic fiber blanket for insulation. They're great and small. The AS oven from the book looks pretty easy and straightforward. I have found floor thickness to be irrelevant. My oven (hemispherical) has 2.5" thick floor and about 6+" walls. Holds heat great over the weekend.
Thanks for the response.
So what I am hearing is that the use of additional insulation is warranted. So, where does the fibreboard fit in the slab/construcution? Do we retain the 3" vermiculite/cement, the concrete slab, and the fire brick hearth. Does the fibreboard go below the vermiculite, between it and the slab, or above the slab (and if above, wouldn't this reduce the thermal mass?)
For the dome, I presume that the fibre blanket is used in place of the loose vermiculite layer. So you would have walls made out of firebricks, coated in foil, then 90mm (3.5") of concrete, then 50mm of blanket, then waterproof coating?