Intro: This project was the result of a concern about the wasted sawdust being dumped / burned that could instead be used for heating purposes.
This stove was purposed to give horizontal radiant heat, as well as a cooking surface, for the duration of a guard’s night duty. Tests proved that this stove could exceed 11 hours of burning.
Main Design: 
Air entering the airtube (through the small hole in the restrictor plate), proceeds to the bottom centre of the stove and is drawn up into the burning tube of the inner drum. The heat rises, striking the underside of the hotplate and is forced to spread outward then down the annular space between the inner and outer drums (giving a hot drum wall) before escaping up the chimney situated half way down the outer drum side. The chimney (when hot) provides a slight vacuum that not only maintains the incoming draught and combustion but ensures that no fumes escape from the stove into the watchman’s hut.
The Outer Drum: may be made 
from a 20kg gas bomb (OD of 30 cm), cut horizontally 40cm up from the base. Cutting from the side into the base of the cylinder, one can fit the air intake tube (75 x 40 mm), leaving some 50 mm outside (in which the restrictor plate can later be inserted). Half way up the “back”, one can cut a 50 diam hole for the chimney – a 2” galv “Tee” welded on the outside.
The Inner Drum: must be 2 cm smaller in diam than the outer drum, sit nicely on top of the air intake tube spigot and finish about 2 cm lower than the top of the outer drum. It may be made from a cut up 20 lt oil drum or from another gas bomb with some 6.3 cm cut from the circumference before re-welding it back into a 28 cm circle (a new base would need to be made). The base must have a central hole cut at approx 30mm diam. The drum must be removable (for fuelling and ash disposal).
The Chimney Tee: A spigot (10 mm diam) should be welded to the upper-facing exit, to support the 
3” diam chimney stack. This spigot allows the chimney to be removable but to be reasonably sealed. In the lower-facing exit, fit a 2” bung from an oil drum, with a hole drilled in its centre. The hole allows chimney condensation – and there is a lot! – to drain out into a plastic cup placed below to catch it.
The Air Intake Tube: is made of 75 x 40 mm rectangular steel tube. The inboard end needs to be sealed up, but a rising 30 mm extension must be welded on to meet up with the bottom hole of the inner drum. Again a spigot is suggested, to ensure a reasonable seal with the inner drum and to lend support to it. At the outer end, a slot needs to be made from above to permit the restrictor plate to slide in neatly, effectively blocking the air tube (when inserted).
The Restrictor Plate: can be made of 2 mm sheet, having a 6 –7 mm hole drilled in the middle (to 
allow meagre amount of air in) and having a short length of chain welded to the top – the other end of which is welded to the outer drum (to prevent loss).
The Hotplate: 
is made from a disk of 2 mm thick steel sheet welded to a band of 5 mm thick bar. It must be a reasonable fit with the top of the outer drum. Handles should be welded to the opposite ends. Some form of insulation may be fitted, as it may need to be removed during 
operation, and will be hot!
The Concentrator: This is a thin sheet disk with a central hole of approx 50 mm diam and 3 locating lugs on the perimeter to slide over the inner drum. The concentrator is needed if any cooking is required on the hotplate, as it has been found that it concentrates the flame for greater intensity – else the hotplate will never boil! For space heating alone, it is not needed.
Lighting:
Dry sawdust must be packed tightly into the inner drum, using a pounding stick. (The tighter the pack – the longer it burns!) However, first, a smooth 30-40 mm diam tube must be found to act as an air tube former. An old shock absorber is very good for this. When the sawdust has been packed, remove the airtube former carefully, using a twisting motion and position the concentator plate onto the inner drum. This should leave a neat hole down the centre of the sawdust directly above the air intake tube (which should be seen!). An oil soaked rag may be lit and stuffed into the airtube from outside, so that the flames sweep up the vertical airtube in the sawdust. It may be an idea to position the (removable) chimney on top of the concentrator plate, not only to encourage the initial combustion, but to warm the chimney and so encourage a good draft when the chimney and the hotplate are returned to their proper stations. After some 15 mins of burning, the restrictor plate may be inserted in place to slow combustion for the night. If more heat is neede, the plate may be left out, but the burning time will be shortened and the fumes may escape from the stove top. (It may be better to make a larger air hole in the plate).
Final notes:
1. 
Make sure that the chimney is designed to rid the hut of all fumes – they are most obnoxious. Properly set up, the stove should provide a fume-free environment inside the hut. To prevent rain entering the chimney, it is suggested that a short piece of larger-diam tube be welded onto the top of the chimney, such that the lower join is open, allowing rain to run out.
2. Make sure that the outer drum is removable. It will need cleaning and some ash/sawdust will collect in the outer drum ad well as the inner one (although most ash will be removable with the inner drum). The chimney also will need de-coking periodically.
3. A poker/hook (from 6mm def bar) is advisable for positioning the burning rag and occasional cleaning out of fallen ash from the airtube.
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