earth-n-straw
technology to build naturally

Newton's Wood Fire Oven

My inspiration to build a wood fire oven in 1995 came from three main sources. Colin, my husband who talked endlessly about a mud brick house his family were building; an article in the Earth Garden; and a back yard full of high plasticity clay. Here is a picture of our wood fire oven next to our straw bale wine cellar. This is suburbia at it's best - the brick veneer building in the background is our next door neighbour.

Designing Phase

Before starting to build our oven I did my time at the state library. It was well worth the effort as it was necessary for me to get my head around the need to put chimneys, oven doors and vents into the plan. What I found out is the basics of wood fire ovens:-
(1) There is no chimney. A chimney would act as a route in which rising heat would escape.
(2) There are no doors on the oven. The doorway is how the oven breaths. Cool air will be drawn in at the floor of the oven, provide air for the fire, the hot air (along with any smoke when you are starting the oven) will rise to the ceiling of the oven and come out at the top of the oven door way.
(3) The height of the centre of the oven should not be any higher then 350mm. A higher ceiling will encourage the pooling of heat in this area instead of the floor of the oven where the food is cooked.
(4) The doorway should be 2/3 the height of the ceiling. This encourages the storage of heat within the oven. We never had any difficulty with the oven breathing.
(5) The width of the door was wide enough for your widest cooking dish and your hands on either side. Our doorway was 400mm wide, though we would go wider next time so that we could put two small pizza trays in next to each other.
(6) The height of the oven floor above ground is working height. I would suggest slightly higher then bench height.
(7) The internal size of the oven. Ours was 1200mm round. This gave us plenty of room at the back to push the coals, leaving room at the front to cook.

The Building Phase

With my head around these design concepts I was next faced with the challenge of engineering and basic building concepts. Armed with the vision of what I wonted, and no building background, my first structure failed. At this point Colin stepped and got my plans back on track. No wonder I married him.

(1) Build your structure up to floor level. Use whatever suites you aesthetically. Recycled bricks, besser blocks, timber post, cob or mud bricks. Underneath becomes a great storage area for timber. An opening for this, as wide as the oven would make it easy access.
I used cob for this. A mixture of clay, straw and some manure. (I had no understanding of cobbing back in 1995, and the lack of sand caused the clay to remain highly plastic which caused the cracking). The clay was too elastic, combined with the unprotected external environment, rain and high heats from the oven it seemed doomed to crack from early days. So we fixed it. We wrapped in bird wire (for reinforcement) and gave it a concrete render raincoat. Looks great and works perfect.
(2) The floor. We placed some beams across and sat some second hand corrugated iron on this. We then spread a gravel bed over the corrugated iron. We now had a floor to work from.
(3) The floor and side walls of the oven were made from firebricks. We got seconds. They are made for the job with excellent heat retaining properties. Conventional bricks can be used successfully, though they may not hold the heat as long. The bricks on the floor were sat together like pavers. The bricks on the wall were 2 high and sacked in staggered fashion on top of each other.
(4) The roof was also made using firebricks. The roof is dome shaped. We made some framework to support the dome and the doorway during construction, this was made using some thin ply. The ply was cut into wedges, like a pie, and shaped into a temporary ceiling. We used spare bricks, and timber struts inside the oven to support the ply framing during construction.
(5) The firebricks were placed ontop of the ply, radiating from the centre out to the edge. There were quite a few gaps as we radiated out. We later filled these with concrete (or firecrete if your budget goes that far).
(6) 12mm threaded booker rod was run around the full circumference of the domes outer edge and the 2 ends welded together. This stoped the roof wanting to spread and cave in once the temporary support is removed.
(7) So with the roof in place with the booker rod around the edge, the gaps in the ceiling were filled with concrete and allowed to set. The spare bricks supporting the roof were easily removed. The ply and timber struts were burnt out on the first lighting of the oven.
(7) Finished as suites you, we have 3 friends whose finishes are as varied as there personalities. They have chosen bricks to blend in with a suburban house, concrete render to blend with rockery next to a pool, and an earth render.

Getting the fire going

A fire needs lots of oxygen to get established. Light the fire in the mouth of the oven. Once it is well established, push the fire back into the oven. It will take you a bit of time to become competent at reading the ovens temperature. But through a little practice you will know your ovens temperatures as well as you know your bath water temperature. Invest in a set of welding gloves as this makes turning the dishes somewhat safer. I melted the nylon kitchen mitts on the first night.

Cooking and the good life

You will be only limited by your imagination. Get to know your oven. Experiment. This oven will make your cooking famous, as it does not taste like a conventional oven. Use the oven floor instead of tins to finish cooking your breads and pizza. We baked breads, pizza, biscuits, curries, casseroles, roast, whole snapper, and when the oven became cooler at the end of the night we used it to drying foods, and slowly cook the porridge so it was ready for breakfast. We've had many a quiet dinner for 2 and a quite a few parties. Friends turn up from everywhere with pizza toppings when they here the oven is on. It makes short work of putting on 25 pizzas for Saturday night.

We are currently in a lost phase between wood fire ovens as we build our new home, but if our building project plan is anything to go by, we shall be cooking in the oven again for Christmas 2003. That reminds me of the Christmas we had with 7 good friends back in 1999, we put on the oven and had so much beautiful food. We couldn't possible fit in the whole snapper, so we put it in the oven at 1am before going to bed - it slowly cooked over night and made a perfect breakfast treat.

Wood Fire Oven - The Newton's Design II

We feel that it will be a shame to burn timber without making maximum use of the heat released. This is why we like the design of a wood fire oven - minimum fuel with maximum storage of heat. Our next wood fire oven will provide two added features that will interact with our house.

1. Ducted Hot Air - The house can be heated using thermosiphoning. When hot air rises cool air to be drawn in from below. A pipe will pass through the back of the wood fire oven, the inlet will be below the oven where fresh air can be drawn in. The air is heated as it passes through the oven. The outlet will be higher and vented into our bedroom. A valve at the outlet duct will close the pipe when heating is not required.

2. Slab Heating - A copper pipe will coil in the ceiling of the oven. This will be a closed circuit pipe filled with water. As the water heats it will thermosiphon through the pipe which is laid in the earth floor in the bathroom. The earth floor acts as a thermal mass and stores the heat so that my feet don't get cold. As our bathroom floor is suspended on the second floor, we have insulated the underside of the floor with second hand insulation foam to prevent the loss heat through the bottom of the floor. Again a valve can turn off the flow of water through the pipe when added heating is not required in the house.

Links

If you plan to build any type of wood fire oven then you must visit the Masonary Stove Builders - Brick Oven Page.

For those who need to do more then cook pizza, have a look at Igor Kuznetsov's site. This will take you from heating a house to building a Russian Sauna.

Our friend, Will Henare, with his pizza creation