Hello from France

[Nos]

Iam English and retired from the medical proffesion and I have some Accrington fire clay bricks left over from a project I also have a genuine French oven door to use, so why not build an oven I thought. A couple of question's, I dont want to build a dome type but just a rectangular one with a curved ceiling, also as a railway enthusiast, why is the chimney put at the front, over the door? you get more of a draw where the incoming air travels over the fire and out the back. Iam of the opinion, and it not my intention to upset anybody on my first post, but just because the "Traditional" oven has been built this way for thousands of years, why we cannot change, or improve it, any comment would be welcome. take care. Nos

[david s]

Having the flue at the front of the oven does seem odd at first. It makes the oven more difficult to work having a tunnel to work past before reaching the oven proper. I was also of the belief that it could be improved on. For my first oven I based it on the design of ancient Roman kilns ie a hemisphere with the vent at the apex of the dome. The draw was terrific and no smoke at start up and no tunnel to have to work past. However, unlike a kiln which is full of wares and shelves an empty chamber results in the flames diving straight for the flue resulting in poor circulation and a lot of heat loss out the flue. This is known as an updraft system. Modern kiln designs employ a downdraft system whereby the flames rise in the chamber and are pulled down to the bottom where they exit to the flue at floor level. This results in good circulation, even temperature distribution and good fuel economy. The hemispherical oven with the flue at the front is somewhere between the two. It is more of a cross draft system whereby the air enters the chamber, combines with the fuel to swirl around the dome and is then pulled down a little to exit at the top of the door. To get the chamber atmosphere right virtually no flame escapes the chamber and the full length of the flame is useable and stored heat. The only down side is a smoky oven at start up unless managed correctly or until the flue gets hot, as well as the entry being in front of the oven. There are lots of small updraft ovens at Pompeii and these were probably in people’s homes where keeping smoke out of the house was probably more important than fuel consumption. The big oven at the bakery is of the cross draft variety.
A square oven with a large radius vault for the roof as used in bakery ovens is inherently unstable as a structure and requires steel bracing of the walls to prevent the vault’s sideways thrust pushing out the sidewalls.

[Nos]

Thankyou very much indeed, I will modify my design for the flue to be at the front . The floor area is 70x110cm it will be double walled ie the inner will be brick, then insulation (Perlite, fiberglass) then the outer wall concrete block with a render, the height of the oven is based on my door size so the internal wall height is 45cm riseing to 65cm in the "ceiling" the floor will be a 100mm layer of reinforced concrete then 100mm of perlit concrete, I will use fire bricks as a removable floor for the oven, it will be outside but under a tile roof, to keep the oven and myself dry, and not water down the beers thanks again. Nos