What is the right size oven? Whether for home, bakery, or restaurant, the answer is always the same: the smallest oven that will meet your neds.

For home use, an oven that is three feet in diameter (90cm) is usually sufficient, and I would not go bigger than three by four feet. Smaller ovens are easier to manage. It takes less wood to heat them, which makes it easier for the city-living operator to gather enough fuel to fire it on a regular basis, and they heat faster than large ovens, which means it takes less time between starting to fire an oven and baking.
For you are interested in an oven primarily for making pizza, please see my page on Pizza oven Basics. Conceptually, you want the smallest oven that will meet your needs. The smaller the oven the easier it is to afford to maintain a high temperature, e.g. never much below 650F. The hotter the oven the faster you can move food through it, so a small oven that is maintained at a high temperature might turn out substantially more food in a restaurant than a larger oven maintained at a lower temperature. For a commercial bread bakery, oven size is determined by the output needs of the business, but would typically be two to three times the size of a home bread oven.

What should the oven be built of; how massive should it be? What you build an oven out of — and how much of that material you use, which is a matter of how thick you make the walls, depends on how you will be using the oven. The longer you need to maintain the oven at cooking temperature the more the material you use should reatain heat, and up to a point, the more of it you should. Use on the other hand, it is not efficient to make an oven more massive than necessary.

The home cook — and this includes me — usually bakes for a period of three or four hours, five at the most. In practice, most home bakers bake a couple pizzas, roast a chicken or a leg of lamb, roast potatoes, bake a loaf or two of bread, and bake a dessert, like a pie. This, roughly, is how I typically use my oven. In contrast, a commercial bakery might actively bake in their oven for twenty-hours, using it through multiple shifts. The commercial use pattern migh be twenty hours of baking, two hours of firing, two hours of cooling, and then once again twenty hours of baking. The home baker doesn’t need an oven that stores enough heat to still be baking eighteen hours after the fire was removed from the oven. Thus, the short answer to the question of how massive ones oven should be is that the mass should match the demands you will make of the oven. The home baker’s demands tend to be modest, and so the the home baker can do just fine with an oven that has an oven wall made of adobe, or a comparatively thin layer of refractory concrete, while a commercial baker requires an oven made of a material that stores the most amount of heat possible, like stone or brick, or like a refractory concrete shell thickened with regular concrete. [Note 3]

The issue of mass — and how long you can cook in a single firing — has four components; the nature of the material used to construct the oven walls, wall thickness, the oven firing schedule, and how well the oven is insulated.

• Oven Mass: There is a direct correlation between the weight of a refractory material and its ability to store heat. Denser materials store more heat than lighter materials, thus granite holds more heat than bricks, and bricks hold more heat than adobe.
• Oven wall thickness: The more mass an oven has the more heat it can hold. Thus the thicker the wall the more heat it will hold. This is really the same as saying that the more the oven weighs the more heat it can hold. Most pre-fabricated ovens have walls that are about 1 1/3 to 3 inches thick (3cm to 6 cm). [Note 4]
• Oven insulation: When you burn a fire inside an oven you can think of yourself as stuffing heat into the oven walls. Once you stop firing the oven the heat radiates out of the oven walls equally in all directions. This means some of the heat radiates back into the oven — and some of it keeps traveling through the wall of the oven out the other side. Insulation retards or even stops heat from being lost out the sides, top, and floor of the oven. As general rule, insulation is cheaper than the material the oven is made out of. Insulation is therefore a good investment because the better your oven mass is insulated, the less mass you need to achieve the same baking goals. Modern industrial insulation can effectively stop heat from escaping out the top, sides, and bottom of the oven.
• The fireing schedule, the Flash Fire: For most non-commercial uses the oven is brought from cold to baking temperature in a single firing that lasts 1 1/4 hours to 2 hours, with 1 1/2 hours being average. You can think of this as a “flash fire.” The object is to burn a fire that is as hot as possible until the walls of the oven are white hot and you have achieved secondary combustion. You know you have secondary combustion when you see a cloud of fire hanging just under the oven ceiling. Regardless of the mass of the oven, a single flash firing is sufficient to heat the oven for several hours of baking. A supplemental fire can be built within the firebox after a few hours if you need to continue baking and the oven is cooling too far, for example, if the oven has dropped to 300F after four hours and you want to keep baking in an oven that is 350F then a small supplmental fire will bring the oven back up those few degrees, and keep it there as long as you need it.
• The fireing schedule, the Lost Fire: The baking potential of an oven is ultimately defined by its mass. A massive oven, one capable of baking for twelve to twenty hours at a stretch without refueling, must be saturated with heat in a preliminary firing in order to perform at its maximum potential. Once the super-massive oven is soaked with heat, then, depending on the rate at which the oven loses heat, but typically only once in a twelve hour period, the oven heat is refreshed with a flash fire. This “lost fireing” as the French call it feeds heat into the oven so that the oven walls are in the range of 950F for a depth of several inches. This firing can take a long time even twelve hours, or more. To maintain this long firing one may burn logs rather than faggots and other fast burning materials, although here, too, the hotter the fire burns the more efficient the fire.

An rough putting things together: If you want an oven so you can do some baking at home, roast a chicken, a leg of lamb, bake pizza, bake a few loaves of bread, a pie, etc., one does not need a super massive oven. If all your cooking is taking place within the space of a few hours, then you only need an oven massive enough to hold heat for a few hours. You can also, as one sees restaurants do, operate the oven with a fire going inside the firebox while one is baking. Thus, if one finds that after baking the pizza, the chicken, and the bread that the oven needs a little boost for the pie, then one can always keep a little fire burning in the oven while the pie is baking. On the other hand, if you want to operate a commercial bakery and bake in the oven for twenty-hours at a stretch — starting with flat breads at 4 a.m. and ending up with cookies and meringues at midnight — then you need an oven that has enough mass to stay at baking temperature for twenty-hours after the end of the one daily firing.

About how much does a home oven cost? As with so many things, you can pay what you want. At the cheapest, you can build an oven with a wooden base, vermiculite concrete insulation, a brick floor, and a refractory concrete shell for under two-hundred dollars. You can build an adobe oven for the price of a bale of straw. A pre-fabricated oven, installed, or a brick oven, if someone builds it for you, can easily cost between eight and twenty-thousand dollars.

Can I build an oven? Building an oven can be simple or complex, depending on what you want and your own skills. A friend of mine, a contractor, once came over to ask me what the dimensions of an oven ought to be. I gave him a set of dimensions — three feet in diameter, a roof twenty-two inches high, and a door sixty percent of the height of the oven roof, and three days later he had built it. The Bread Site of the Masonry Stove Builders is the best place online to start looking at home oven projects. The best book for adobe ovens is Kiko Denzer’s Earth Ovens. There is a detailed book describing a brick oven in detail by Tom Jaine called Building a Wood-fired Oven for Bread and Pizza. The Bread Builders by Daniel Wing and Alan Scott also describes how to build a brick oven. If you read French an excellent book on building ovens is Constuire, restaurer, utiliser les Four a Pain by Michel Marin. If you are interested in period ovens for a Colonial American house, then you might try to find The Forgotten Art of Building and Using a Brick Bake Oven by Richard Bacon. My own oven is built on a wooden base — I used logs from a plum tree that I cut down in my backyard — vermiculite concrete for insulation, common red brick for the oven floor, and refractory concrete for the shell. My total cost was under two-hundred dollars.

Can I buy an oven? Yes. I include a few links to American bead oven companies on my equipment links page. Many American companies import bread oven kits from Italy. Wherever you live, therefore, you should be able to buy a kit from Italy. Alan Scott, the co-author of The Bread Builders builds ovens for people, and sells plans.

[Note 1] I want to emphasize the importance of the material’s ability to absorb heat. I recently met someone who built an oven using materials that are used to build kilns. He was being advised by a kiln-builder. Kiln walls and shelves are made of insulating materials. You need material that will absorb heat. The insulation is another and different oven layer. Kiln materials can be — are — fantastic for insulating the oven shell. But don’t use them to build the shell or oven floor.