Biochar Multi Heater

The Biochar Multi Heater.

Biochar producing pyrolisis stoves are very efficient and clean burning. However, using one in as a hob with a simple cooking pot is very inefficient, only a small fraction of the heat generated is actually captured and used.

If we are to make the transition from fossil fuel  dependence and become less dependent on the energy supply companies, then it makes sense to maximise efficiency of heat capture in order to enssure that there is enough wood to go round.

With this in mind I have designed a simple yet effective oven, griddle, water heater and space heater all in one, designed to be used in conjunction either with tlud stoves or biochar rocket stoves.

How to make the Biochar Multi Heater.

In order to make this you will need a good welder (a mig capable of welding at least 5mm mild steel), an angle grinder and a cut off saw will also be helpful.

It is possible to vary the dimensions used here whilst maintaining the basic principles.

figure 1

1. Start with a stainless steel cylinder, walls at least 2 mm thick. This one is 30cm diameter and 40cm deep. (I obtain second hand metal by going to scrap yards and offering over the price for the weight of the metal as scrap). Alternatively, a length of suitable pipe can be bought from steel stockists.

This cylinder will be the oven.




fig 2

2. Cut a square sheet of stainless steel (s/s) 42 X 42cm. (I used a section from an old catering table).

Cut a 28cm diameter hole in the middle of the s/s square and weld the oven cylinder over thehole as shown in fig 2. (I used 316 grade s/s mig wire to weld).




fig 3

3. Take a 50cm long section from a 38cm diameter cylinder as the oven surround. Cut a 20cm diameter hole, centre about 18cm from one end of the cylinder and weld a 20cm dia. collar (about 15cm long) over this hole.

Cut a 28cm wide section from the opposite side of the oven surround,




fig 4

4. Cut a rectangle of mild steel 5mm thick 55 X 42 cm as the griddle. Cut two lengths of 6

cm square angle iron, each 55 cm long. Weld the angle iron to the bottom of the griddle, 28 cm apart, as shown in fig 4.





fig 5


5. Place the oven cylinder into the oven surround spot weld the square plate onto the front of the oven surround. (it san be seam welded later when you are sure it is positioned correctly, see figs 5 and 6 for positioning).




fig 6


6. The griddle should be able to fit over the oven front plate and the angle iron on the griddle should line up with the oven surround. Tack weld the griddle in place.





fig 7

7. Cut and weld a baffle to go behind the oven and 2 baffle strips to run between the oven and the oven surround. This is to divert the heat round the oven and up to the griddle plate before it goes down then up through the flue.






fig 8


8. Cut a 42 X 42 cm square of 5mm thick steel as the back plate. Cut a 12 cm dia hole towards the bottom, in the centre of the back plate as shown.





fig 9


9. To make the oven door you will need the 28 cm disc cut out from the oven front plate, a 30 X 30 cm sheet of s/s and a few scraps of metal for the door catch.





fig 10


10. Weld the disc on to the centre of the square oven door, using a few (5mm) spacers in order to hold it away from the door.





Fig 11

11. Weld the door in place with a strong s/s hinge.







fig 12

12. You will need to make the flue outlet and a water heating cylinder. Using a cut off saw, cut a length of at least 12cm dia. pipe at a 45 degree angle in order to make an elbow.






fig 13

13. The heat exchanger is a length of 9cm dia. s/s pipe (about 60cm long) welded inside a length of 12cm dia. s/s pipe using a 12 to 9cm reducing bush at each end.

I cut a half inch s/s barrel nipple (available from a pipe fitting supplier) in half, cot a half inch hole at each end of the 12 cm pipe and welded each half of the barrel nipple over the holes.

At one end of the heat exchanger is a 5″ flue pipe attachment. At the other end is a piece of pipe to slot into the outlet collar on the back plate.



fig 14


14. Weld the elbow together and weld it onto the hole in the back plate.






fig 15

15. The heat exchanger should fit into the flue outlet collar.

The heat exchanger can now be connected up to a household copper water cylinder or it can be rigged up straight to a header tank and used as an urn.





fig 16

16. Make an oven door catch out of some offcuts as shown.







fig 17

17. Make a table and frame to hold the all in 1 heater at the required height above a tlud or a biochar rocket stove.

Complete all seam welds.






fig 18

Making a hazel cupboard for a copper water tank to be connected to the water heater.







flange welded to bottom of heater

Instead of sitting the heater on a table and having a biochar stove under the table, if the heater is to be used in conjunction with a biochar rocket stove with feed and emptying hoppers (i.e. a stove that does not need to be removed) then it can sit straight on the stove. This picture shows a flange welded onto the bottom of the heater with tabs cut out of the flange so that it can be bolted onto the top of the stove.




heater attached to top of stove

Here the heater has been attached to the top of the stove and the pipework connected to a domestic 100litre hot water tank.