stove building workshop

As we arrived in Clos du Doubs, we met Krishan an old and wise clay-oven-builder.
He was there visiting Niccolas and build with him the new oven for the upstairs-rooms.
The oven should be used to heat the upper rooms and for baking food and drying fruits.
We came totally to the right time,
they already build up the fundament for the oven and made some skizzen,
but they already were at the beginning.
Some of us were very interested in learning how to build an oven made of pure nature clay and sand.
so we started to help them to build up the oven brick by brick.
While building up Krishan told us about ovens and we learned in practical way.
In the evenings he gave us lessons in oven-building-theorie and how he started to build up clay-ovens.


Here you can find an instruction for building the oven that we built:




Chapter one: chimney


A chimney is a rope or a duct which normaly goes through the house vertically up to the roof or sometime just go out the oven self.the chimney has the function to suck out the air and the smoke of the oven and suck new air into the fireplace to heat up the fire and keep it alive.
so more high a chimney is, so more sucking-power it has.
But why is that so??
The nature tries to balance everything. When you put hot water in cold water it mixes it up and balance the temperature.
The same it is with the airpressure.
in higher areas we have lower airpressure than in lower areas.
At the fireplace we have more airpesure than at the top of the chimney, so the airpressure press automatically the steam and smoke of the fire up through the chemney to balance the airpressure-differences.
At the same time:
The air gets heated by the fire which is more hot than the outside air.
Hot air is more light than cold air and rise up streight.
so it is flowing throuth the chemney up and generating an underinflation which sucks new air from the bottom of the chimney through the fireplace and keeps the fire alive by feeding it with oxygen in that way.

how big shouls a chemney be?
5-6 meters tall is minimum size
also the diameter should be not too big, minimum size is 18cm = 220cm²
you can calculate the cm²
by round chemneys with following formul: r²*π (square radius, multiplicate with pi)
by cornerd chemneys multiplicate the length and wide of the chemney-sides.



in older buildings, the chemneys where build very big that chemney-cleaners were able to climb into the chemney.
for the most ovens its too big, and sucks too bad so it could be useful when you build in a smaller tube, you will have much more sucking power. but be careful, ask your chemney-cleaners there are everywhere different strikt rules about ovens and chemneys.

also when the chemney is too big the smoke will circulate inside and go much slower up.when the chemney is small it goes up streight and fast.

when you build the chemney with bricks you will have the effekt that the bricks will heat up by the hot smoke of the oven(s) and heat the areas where the chemney pass by and be a heater at the same time.
when you use a tube inside the chemney which is isolated from the walls, you willnot have this effekt.



You also always have to look when you build a chemney,
which main wind-direction you have, this is important for knowing how you should build it.
also when your chemney is smaller than the top of the roof it can happen that the wind hit the top of the roof, start to squirl and press air into the chemney.
So the smoke cannot go out and get pressed back into the house.

Also very important is the location of your house and your surrounding.
Is a house build on the top of an hill, where the air runs up on the side and helps to press out the smoke of the chemney is better as a house which is build in a forest where much trees are growing beside which are taller than the house
where air fall down at the trees and could press the smoke into the chemney.

an fire also starts bad if you have too low airpressure outside or the chemney is too cold,for that you can use a trick.
go down to the cleaning-clap of the chemney in the basement and start a short and very hot fire with newspapers there.. so you will heat up the chemney very fast and you can more easy start a fire in the oven.
in german it is called "Lockfeuer"



chapter two: the oven

there are differne kinds to build up ovens.depends on what you want.
if you just want a simple ofen for heating the room you just need a fireroom and a channel go up to the chemney,
but you can use the hot air going out of the fireroom much more efficient when you lead the hot smoke of the fire around in some channel-systems before you let it flow into the chemney.
so you have much more stone-area which get heated up and ray the heat into the room.
you also can build a sitting-bench on this smoke-channel-system so you have heated bench.
there are no boarders for your creativity.
I just want to show you one example of ovens and its aircirculation, that you get an first impression about the functionallity of ovens.
and some very important things you should attend.

first and most important:
fire produces different gases.. some of them keep stick on the top of the ovens fireroom.
they are very explosive and when them get in touch with some fresh air they will explode and distroy the hole oven, some people also died of that effect.
so most important is in every kind of oven you build.you need to build an so called "shortcut" this is the shortest way connection between the fireroom and the chemney, so the gases can always leave the top of the fireroom and flow suddenly into the chemney.
for that you build a small tube for that and build also a clap between the fireroom and the tube where you can open and close the tube but you have to make a small hole in that clap.
it has also following side-effect:
when you start the fire you open the clap, so the chemney can suck the air of the fire in the shortest way and you will have a stronger sucking and pressure which helps to start the fire easily, cause the hot air and smoke dont get lead through the channel-systems.
when the fire is burning you close the clap and so the smoke gets lead through the channelsystem and heat up the hole oven.
the hole in the clap has the function, to suck all the time the gases out of the fireroom and lead them suddenly into the chemney.

so you have the fireroom, it is the room in the oven where you burn the fire in.
this will be the most hot place of the oven and it is important to build up this whith good stable materials.dont use pure clay-bricks and normal clay-sand-glue for it, it will break.
better is to use schamott or firebricks (the red ones)
Schamott is in compare to clay made of a mixture of clay and little stones and pressed under much higher pressur.
The Schamott-bricks has to be clue also with much more fine clay-sand-mixture.
The pure clay-bricks just get clue by more gritty mixture of clay and sand.
this is cause the schamott-bricks can handle much more heat than the clay ones. they dont get so easy brittle like the more gritty glueing-mixture and the clay-bricks.
the fireroom should be between 90cm and 120cm tall.
at the exit of the fireroom the smoke has about 1000 degree.

from the fireroom the smoke will flow through a channel called "Ãœberbrandt* (german) there it has 900 degreeand runs down the (Sturzzug) to a channel which is under the fireroom,
there you let lead the smoke through different channels up to the chemney.
so more way you have so more stones will get heated up, but also so slower the smoke will flow and when it is too long the chemney willnot suck it anymore.
there is no standard data how long it can be, it always depend on the power of the chemney and how the oven is build.

the diameter of the channel leaving the fireroom should be the biggest one,
the smoke get more and more cold on the way to the chemney, so we can reduce the channel-diameter on the way to the chemney.
so we also have a better smoke-flowing and the pressure from the chemney can suck better and more consistand.
on the bottom channel of the oven we have to add 20% more cause there ash will stuck over the years and we need more space to suck the smoke through.