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More on rectangular dome and round floor igloo dome types:
Rectangular floor dome and round oven circular dome sizes.
Below are two dome examples, 34" x 38" or 87 cm x 96.5 cm internal rectangle floor-space cooking area (barrel oven) and 34 inch or 87 cm round internal surface.
Same width rectangular and round domes
and fire positions diagram.
Circle area calculation: A=π.r² (π = 3.14 and r² = half diameter²)
Which dome is better to use, rectangle or round dome?
I receive many emails on this, people think one dome is better than the other. You will cook the same high quality pizzas in the rectangular barrel oven dome, as you will bake lovely breads in the round dome. In principle both dome types cook "exactly the same way." You will not get cold spots in the rectangular dome as well as you won't be disadvantaged with baking smaller breads in a round dome if you're not production baker (high quantity bakers prefer rectangular floor for the space reasons.)
Same width rectangular and round domes
and fire positions diagram.
In refractory industries; metallurgy, cooking or ceramic - huge, big and small furnaces, ovens or kilns (high or low heat levels) firebrick hot face chambers use rectangular or square floor shapes with walls and arched ceiling - vault, they are easier to make and last very long. In my work with refractory for large metal companies or other small ones, it would be hard to imagine them using round igloo or half avocado shape chambers. Technically not space wise, round floor chambers will do the job the same way when in a production but these domes are harder and costly to build properly. When built improperly igloos won't last. Other case would be if you plan to experiment with a short term wood oven, without a properly functioning flue (upwards hot air passage for the exhaust and also cold inlet) and chimney, such as adobe mud oven, or if you plan to use it only rarely.
Lamb leg and beef roasts with
1.5 Kg - 3.3 lbs rye bread loaf
Rye bread beef roast mustard sandwich
And their fellow colleagues just adore them and some even love them. Easy maths;
60 (sixty) nice muffins
baked in brick pizza oven
Back to the subject - In this respect; heat never falls down (it can not fall), it radiates to every direction from every single pixel point on walls through meals, logically it is the physical law e.g. heat from the sun. Like the shop owner wanting to sell you not good blue candles, he knows it but they make him bigger profit ... He says "they burn longer" ... but We know this is not so because every candle burns only shorter and shorter.
If you wanted to speed up heating time in traditional wood fired oven, you would have to make the dome walls thinner and oven will heat up only 10-15 minutes quicker, but then it cools down faster, so you can use it mostly only for pizza while fire or red embers are alive. Well insulated or not, use of an oven with thin refractory thermal mass is limited.
Thicker/wider refractory oven walls are good for ecology, planet, firewood amount usage, oven efficiency, your pocket and cooking variety. E.g. you start to do pizzas in the same time as in thinner wall dome, but when your walls have bigger heat absorbing mass, then while you make pizzas in higher pizza making temperature the dome is continuing to absorb more heat energy as it has bigger heat absorbing capacity available. When you stop to make pizzas embers may be left to die down and your oven will be hot for longer time. This is very practical for many other activities after pizzas if you go for quality. After fire is left to die down, you will roast or bake cakes or breads in previous heat energy stored for 5 hours. Still after that use additional 10 hours for fruits or halved tomatoes drying time, for your toppings, all home made!
In both types of domes, heavy firebrick walls absorb heat from fire. For they high bulk density (1860kg/m³) all firebricks have very good heat conductivity so energy gets quickly spread everywhere in the medium equally creating evenly heated domes. (Like aluminium turns cold fast, so can heat travel within firebricks and make them very hot. Like sound travels fast in the water. Dense material conducts heat fast, air spaces in heat insulation slow it down.) The floor is usually few degrees colder. Inside the oven, this heat energy is distributed by radiation and it radiates out from every point. Unless you leave pots right next to the entry the temperature is even everywhere, in the center or closer to walls. It is much more easier to cook in wood fired oven then in a conventional oven where the heat radiates from one side-single energy source e.g. gas burner or el. power heating element.
Structural and building differences in barrel and round brick ovens
After the first half in round igloo dome construction, gaps between bricks start to appear making it very hard to lay all firebricks accurately.
Gaps between firebricks in forming
round oven igloo style dome.
What it means? Inside the dome chamber, on the hot face, brick's edges have to be joined side to side (border to border.) Otherwise lots of mortar is required both in horizontal and vertical gaps between firebricks. It's fine at the bottom but the second half towards the top produces larger and larger gaps and too large in the last ~30% of dome forming. As soon as thin gaps start to appear bigger adjusting and cutting of bricks must start. Gaps between bricks on inside filled with mortar weaken the oven. These bricks get loose (wiggly) if there are gaps filled with mortar between them. After the initial firing, heat differences in material and expansion movements in the dome, mortar won't stay firmly bond to bricks as we knew it while mortaring. Refractory is not as masonry. Refractory mortar thicker than ¼" (6mm) starts to shrinks and crack between bricks which later causes collapsing. Igloo dome does not have the line of thrust-rule diagram line like calculated self-standing catenary arch has as is used in e.g. arches in brick pottery kilns. Self standing catenary arch would have very high vault for cooking oven design (you can calculate low vault catenary arch but e.g. cladding needs to be loaded over to hold splitting the structure to sides.) Also in 'catenary curve arch' kiln bricks have to be cut precisely for it to last. From experience potters avoid mortar as much as possible (pottery is one of the oldest trades), loosen bricks attract gravity as center-top weight pushes towards sides causing collapse. You would have to rebuild it; or might be offered again some commercial pre-fabricated kit (hopefully not some lemon shell) because you already own a platform for a round oven purpose, as it happens. With the addition circular heated structures move not like roofs on buildings - best website on catenary arch and best to read if you are interested!
Have a look at all gaps between firebricks that show exactly how the ceiling would look like from inside - on outside bricks are more apart by the radius, these gaps can't be big too. It is not only the halving bricks. We have here triangles of all sizes, horizontally and vertically forming. These cannot be simply filled with mortar (at least not if you are building lasting quality oven project.) Here is heaps of cutting involved, I personally say a big job just to create only the hot face on inside properly. As you go in circles every following brick has to be adjusted by cutting to align and fit the one before, and so on, the off-cut will fit somewhere later (although usually for another dome.) "... Don't be scared be prepared." With barrel dome types you don't get these problems.
Why do they say a proper oven for pizza is round?
Thin base wood fired pizza ...
Maybe because when red-hot embers are pushed from the center to make space for pizzas this space or the actual pizzas are round. Exactly the same way it's done in rectangular domes too while getting more space. As well as you can bake breads in round dome, as well as delicious roasts can do in both dome types, perfect pizzas are being done in rectangular barrel domes and not only in round. Rather then the shape, the structural sizes are important; e.g. chamber height (vault), door width and height, wall thickness and insulation material. Wood fired pizza is famous, most restaurants selling this pizza have purchased and installed prefabricated round dome ovens, for business it is viable. Logically, this fact could influence opinions too, most people see ovens in restaurant where the pizza is made. Comparing with casting square objects, casting round oven is more practical and cost effective also.
Rectangular barrel style dome
32" x 36" or 82cm x 92cm
Round domes from the past were not made of firebricks as we know now days. When I was a child, in my grandparent's very old house, I used to play and sleep on top of one round oven. "Surely well insulated only pleasant heat did soak up through ... come on, what do you think of my grandparents?" (... Just joking) I witnessed rebuilding it, then they installed wood stove inside and built very good barrel wood fired oven outdoors, it was delightful time for me as a child operating this oven.
Perfect pizza from the barrel
rectangular floor dome.
Heating up a round brick ovens and barrel oven domes.
Traditionally, it's better to heat up ovens slowly using mini fire, so the heat soaked in walls cooks for you for a long time, slow heating process - more evenly heated walls (dense walls have equal temperature on inside and outside, insulation on outside protects this heat not to be wasted through the top - that would be the wrong way!) To heat up oven faster or to keep any type of wood burning dome hot for longer cooking times, it doesn't depend on it's shape (unless you were into scientific precision and be happy with totally minor differences.) It depends on if the oven has proper vault and door heights set, refractory part thickness and bulk density (one part of typical physical properties), heat insulation or if it is design having internal flue with draught/draft from chimney (with 'cold air inlet' when heating up) or more efficient front 'air vent and hot air passage' design. All types of domes can be efficient or not efficient.
Fire heats up the oven.
Concrete cladding and efficiency in wood fired ovens.
Adding concrete cladding layer (ordinary) to any dome adds to the heat absorbing mass. Cladding is dense as well. It is not really an issue if this makes the dome to heat up longer, it does as it has more capacity to suck more energy in but only 20 - 30 more minutes in moderate complete heating of a home oven. For pizza, barrel dome or igloo oven with cladding layer can be heated up in 1 hour (home oven → 82cm x 92cm or 87cm x 102cm which is 32"x36 to 34"x40"), then leave small flame going on to continue making pizzas or finish properly heating up for above mentioned time. Cladding is needed and will not prolong heating time into extremes so no disadvantage (one could be if the dome was thin.*) 5cm (2") of extra cladding layer gives all cooking options making life more amusing (while making pizzas firebricks and cladding thermal conductivity continues to absorb more energy from fire, ten wide walls efficiently release the collected heat very slowly into the chamber.
Continuous fire in rectangular floor barrel dome.
After fire is left to die down, you will roast or bake cakes or breads in previous heat energy stored for 5 hours. Still after that you can use additional 10 hours of fruits or halved tomatoes drying time, for your toppings, all home made!) Many ovens drop temperature fast not holding heat, or floor gets too cold for pizzas (that is common problem.) It's good to have bigger then small mass, it's practical in many aspects, and it is much better. You will not use much more firewood at all because of cladding, imagine wood campfire going on and next to it kitchen type of ordinary BTU gas burner. How many times bigger is the produced energy from wood fire? Many times, and it's only one aspect why wood fired ovens are very practical and pleasing (mate… I slipped off from the main topic again.)
Applying heat back up insulation.
For efficiency insulate* your dome on outside, whichever type of dome you decide to make it's better and logical too.
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