A peep into the inferno of the oil drum inverted burner.

Free tent stove

This post describes how a clean-burning gasifier stove can be made from a 20L cooking oil drum. It can be made with one or two oil drums using a quality sharp knife, tin-snips, drill, handy-man tools, scraps of roofing iron and 7 pop rivets or SH small metal screws.

Introduction to the free tent stove

This post is about making a medium-sized free-standing tent stove from scrap cooking oil drums. It is for those who have a zero budget, no welder but time for creation. Unlike my many other tiny and compact tents stoves for ultralight backpacking, this larger one would probably be limited to based camping, pulk camping, car camping or emergency survival situations.

However, it is a large and powerful stove that provides generous gentle heating and loads of cooking space for an individual or a group of winter adventurers. The stove uses my innovative self-feeding downdraft stick-burner. It is not a true gasifier according to Anderson and Reed. It is a quasi gasifier because the wood gas production and its combustion are not entirely separated.

MY stove design shares features seen in rocket stoves and rocket mass heaters (RMH). However, because my stoves have no heat riser and very little mass and rely on stove pipe draft to develop their power, the experts would not be included my stoves in either of these classes. The common feature is that all three stove types are ‘rockety’ and burn the fuel very cleanly and efficiently.

I use these downdraft burners in all my best backpacking stoves. This means that it efficiently self-feeds a misery 800-1600g (28-56 oz) of sticks per hour and will happily burn damp ‘winter wood’ without a trace of smoke.

Most other tent stoves are batch loaded with a lot of wood and they burn robustly and somewhat inefficiently. By contrast, stoves of my design burn a tiny amount of wood efficiently to completion 13-27g/min (0.5-1.0oz/min ) and the long fuel sticks self feed downwards as they are consumed from only their bottom ends. In doing so, there is no accumulation of charcoal and the wood is converted into clean-burning gas and residual ash. The ash simply accumulates at the bottom of the gas burn-chamber and adds to the insulation of the bottom of the stove that ideally has soil and/or ash added for this purpose.

“I am a person who does not like waste, even with waste oil drums.” Consequently, I devised a simple way of using part of the drum to form the bottom of the gas burn chamber. It can also form an insulating stand on which to mount the stove for cooking and bum-warming. Partway through the build, I realized that an entire second drum could be used to form an even better stand for the stove (That will be the subject of another post that will include other irresistible improvement or refinements).

Lastly, unlike many of my stove designs, I approached this build with some confidence about its success. This was because I remembered the success of a ‘ski chalet stoves’ of my youth. It was a crude but effective upright, top-loading, downdraft stove made from a 200L or 44gallon drum. “Both the design and my youth are now lost but luckily my friends say that I can be immature all my life!”

I have reported on a series of experiments to miniaturise the 44galon drum stove and they worked. So reversing the scaling process was certain to work.

The free tent stove build

The starting point

I started by marking a line around the bottom of the drum so that, when cut off at the line and pressed tightly onto the top portion, it would leave a gas burn chamber with a depth of about 100mm (3.9″).

Oil drum marked ready fro cutting to make the stove. The short portion from the bottom of the drum will become the gas burn chamber and the longer top portion will form the bottom of the gas burn chamber and a convenient insulating stand for the stove.
Oil drum marked ready for cutting to make the stove. The short portion from the bottom of the drum will become the gas burn chamber & cooktop. The longer top portion will form the bottom of the gas burn chamber and a convenient insulating stand for the stove to be mounted on.

The cutting was done with a sharp knife that I use for backpacking camping.

Ultralight wood splitting knifes that I use to cut thin metal sheet. "Seems like cruel thing to do to a knife but if the steel is good then the knife will stay sharp enough to prepare your dinner."
Ultralight backpacking wood splitting knifes that I use to cut thin metal sheet. “Seems like a cruel thing to do to a knife but if the steel is good then the knife will stay sharp enough to prepare your dinner.”

The starting point

The oil drum stove viewed from above. The hole on the right is fitted with stove pipe guard/connector tube made from coffee tin sheet metal. The seam overlap of the tube is interleaved so as to form protrusions that stop it falling into the stove and the stove pipe from falling down over the connector.
The oil drum stove viewed from above. The 60mm dia hole on the right is fitted with stove pipe guard/connector tube made from coffee tin sheet metal. The seam overlap of the tube is interleaved so as to form protrusions that stop it from falling into the stove and the stove pipe from falling down over the connector. The 60mm hole on the left is made to fit a second short tube that becomes an inverted or downdraft burner that holds bush sticks that can be fed down into it. The burner tube can also be made from coffee tin metal. The wood charcoal at the bottom of the sticks burns intensely in the blast of incoming air. Some heat is radiated from the charcoal back into the wood. The wood pyrolyses to make wood gas that largely burns within the stove.

The two portions of the drum were burnt out to remove the yucky rancid remnants of oil and the paint.

The top portion of the oil drum. It will become that bottom of the gas burner chamber and the stand for the stove. It has been burnt out to remove paint and residual oil. The decanting hole has be covered with the bottom of a bean can that was a perfect fit over the hole.
The top portion of the oil drum. It will become that bottom of the gas burner chamber and the stand for the stove. The carry handle has been removed and the clasp has been flattened. It has been burnt out to remove paint and residual oil. The decanting hole has been covered with the bottom of a bean can that was a perfect fit over the hole. Three scrap metal tabs have been fixed to the wall with pop rivets. Metal screws could be used as an alternative. These three stop-points around the perimeter of the stand (one shown in the middle of the photo) keep the cooktop level. More importantly, they stop the very hot expanded gas burner chamber from slipping down over the less expanded stand. Otherwise, they will become ‘locked together’ when cooled.

The internal flame guide

A critical component of all my recent tent stove designs is the flame guide that crudely forces the burning wood gas flame to take a long path to the exhaust.

“Put simply it makes the stove hot by completing the smoke combustion in the stove, rather than completing it in the stove pipe and making it very hot, as many stoves do. I also learned to make them removable/replaceable because such devices will be destroyed, in time, as they perform their duty sandwiched in between Hell and Hades with no way of rejecting excess heat. Consequently, I now reject the temptation of elegantly welding them in place.”

Me

The flame guide spreads the heat over the entire combustion chamber that I call a ‘fire dome’. It creates turbulence to mix wood gas with air for better combustion. Lastly, it acts as a powerful spark arrestor.

For this heavier stove, the flame guide was made out of tough scrap tray-deck roofing iron. This means that it can also act as a thermal shield for the thin drum metal.

The all important flame guide that makes the wood gas and its flame take a long journey towards the stove pipe exit. It experiences temperatures in excess of 1,000C (1,832F), so it should be replaceable. It is made of much heavier metal (waste tray decking roofing iron) that much thicker than the drum metal. The complex folding of the device also makes it a heat shield for the drum metal in the zone of the inverted quasi gasifier burner where charcoal burns at very high temperatures in a blast of oxygen rich air.
The all-important internal flame guide that makes the wood gas and its flame take a long journey towards the stove pipe exit. It experiences temperatures in excess of 1,000C (1,832F) in the corner near the front of the photo which will end up in the charcoal blast zone below the inverted burner tube when the stove is fully assembled. Consequently, it should be replaceable and made of much heavier metal than the oil can metal. I used waste tray decking roofing iron that is much thicker than the drum metal. The box folded shape of the device makes it stable and also makes it a heat shield for the oil drum metal to protect it from the direct heat of the charcoal combustion.

The flame guide can be formed by cutting with tin-snips and simple bending over blocks of wood with the assistance of a hammer or another block of wood. “Just crude percussion engineering and any little mistakes will be hidden from all but your god/s.

The bottom line to this ugly devices is that it makes the stove provide, heat from the wall surface of the fire dome for body heating comfort. It also provides even stronger heating for cooking and snow melting on the cooktop over both chambers.

A peep into the inferno of the oil drum inverted burner. "That intense white glow is indicative of a temperature in excess of 1,000C (1,832F), so it is wise to protect the thin drum metal from its ravages, particularly when excess oxygen is present.
A peep into the inferno of the oil drum inverted burner. “That intense white glow is indicative of a temperature in excess of 1,000C (1,832F), so it is wise to protect the thin drum metal from its ravages, particularly when excess oxygen is present as it must be in stoves of this design that burn so cleanly.

The flame guide was designed to fit across the top of the drum. The other portion of the drum or fire dome was placed over the top and pressed down to the stops. In this positin the top of the flame guide just ‘kisses’ the underside of the fire dome. There is a wide rolled edge on the top of the flame guide and this can be bent more or less to make it a close fit to the fire dome ceiling. When properly fitted, it makes an enclosed wood gas combustion chamber with the flame guide dividing the space into two compartments.

The two combustion compartments

The primary combustion chamber is the largest and hottest compartment where the wood gas is made then burnt. It is turbulent and is strongly irradiated with intense heat from the air blasted charcoal.

The secondary chamber burns the residual wood gas after the residual gas and air passes turbulently through the small hole at the far end of the flame guide.

In the following video the cooking power is on display as is the clean exhaust emissions (Nothing to see!).

Heat shielding

The flame guide can be made to act as a heat shield for the light metal of the drum. This shielding is particularly important in the zone of the pyrolitic burner where there is a blast of incoming air down the inverted burner tube. Here it mixes turbulently with charcoal that is leftover from the pyrolysis of the wood gas or smoke from the tips of the fuel sticks. The charcoal produces temperatures in excess of 1,000C (1,832F) at this point. This high temperature helps to produce the wood gas and make the gas burn cleanly and efficiently.

There also is excessive oxygen in this zone as it is required later to complete the combustion of the smoke as it makes its journey through the two gas combustion chambers. Consequently, the combination of this high temperature and oxygen makes it a very hostile metal oxidising environment.

Extra heat shield for the heat shield

In the charcoal burning corner, any cheap and simple extra layers of thermal shielding are worthwhile, particularly where unlike my tiny backpacking tent stoves, stove weight is not a critical factor.

The flame guide and heat shield mounted on the drum stove stand..
The flame guide and heat shield mounted in the depression on the drum stove stand. If you look carefully, you can see that I have added extra protection for the flame guide in its hottest corner charcoal combustion zone. It is a folded ‘L’ shape of tray deck metal that is fitted inside the corner at the left end and held in place with a folded metal clip. With hindsight, it could have been made much wider to protect more of the drum, as during testing red glowing patches (see photo below) can be seen beyond where the current guide ends.

The photos of the flame guide show that I have added an extra layer of shielding metal to the charcoal combustion zone (in the near corner). It is a simple folded ‘L’ shape of tray-deck roofing that is simply clipped in place with a small piece of folded metal. It would be very easy to replace.

Soil and ash lining

The lining of the bottom of the tent stove combustion chamber with a refractory material was initially done to insulate and deflect the heat away from the stove bottom and the stove stand. I have only used ash for this purpose in my ultralight backpacking tent stoves, as the soil was too heavy to carry on snow trips. “However, luckily, the virgin ash from the immediate wood combustion lays down a delightful light and fluffy layer of extra insulation as the stove burning session progresses.

On this large drum stove, where weight was not an issue, I used both soil and ash as the insulation layer to make a sufficient insulation layer. Even with this protection, and the extra layer of ‘fluffy ash ‘the stand got hot (~100C near the top and 60C near the bottom of the stand ). However, I was delighted to discover that the mass of soil that was used gave the stove a heat reserve that I think made the stove have a resilient stove pipe draft when the stove was allowed to run down.

“I think it was providing mass to what I otherwise might call a Rocket Massless Heater, a different RMH!”

The flame guide and heat shield mounted on the drum stove stand with a liberal layer of insulating ash and soil filling the depression on the drum top.
The flame guide and heat shield mounted on the drum stove stand with a liberal layer of insulating ash and soil filling the depression on the drum top. “The chunks of charcoal were loaded in to help make my first stove start up a roaring success.” This photo best shows the little notch at the far end of the flame guide. Its area is somewhat smaller than the cross-sectional area of the stove pipe. I do this deliberately to increase the velocity of the gas at this point. It means that it creates more turbulence (for better combustion and heat exchange) as the flame and wood gas pass through the sharp edges of the hole and turn sharply around the flame guide.

Heatshield extension

During the first night time test burn, I noticed the red colour of the drum beyond the end of the internal shield. To address this problem I later added a shield extension with a hook shape as a kicker to deflect the flame away from the drum wall.

An evening view of the oil drum tent stove showing the red glow on the side wall of the gas combustion chamber.
An evening view of the oil drum tent stove showing the red glow on the sidewall of the gas combustion chamber. The shield that is part of the flame guide could be extended to this area to provide more protection for the drum metal in this location.
Oil drum tent stove. The flame guide has been extended with an extra curved shield or kicker to deflect the flame away from the wall of the drum.
Oil drum tent stove. The flame guide has been extended with an extra curved shield or kicker to deflect the flame away from the wall of the drum. I made this kicker rather short so that it would not interfere with an experimental side entry port that I had planned for the stove. “The kicker works quite well.”

Fuel and exhaust ports

Two 63mm (2.5″) dia holes are cut in the stovetop as shown in the photo below. Mine were cut with a punch, but they can be cut by hand by the methods described in my DIY hand tools for tinkerers post. One hole is for the stove pipe connector/ guard tube and the other is for the short downdraft burner tube.

The oil drum stove viewed from above. The nearest hole (left) is the exhaust port where the stovepipe guard/connector tube is connected. The other hole (right) is the fuel port where a fuel tube is inserted to form the inverted downdraft burner and feed in a supply of fuel sticks. The steel bar is placed on the stovetop to show the approximate alignment of the flame guide within the wood gas combustion chamber.
The oil drum tent stove viewed from above with the gas combustion chamber fitted over the flame guide that is sitting on the stove base. The nearest hole (left) is the exhaust port where the stovepipe guard/connector tube can be connected. The other hole (right) is the fuel port where a short fuel tube can be inserted. It forms the inverted downdraft burner that guides the fuel sticks down and directs the blast of air down into the inferno of the bed charcoal. The steel bar is placed on the stovetop to indicate the approximate alignment of the flame guide that is largely hidden. It divides the wood gas combustion chamber into two parts, forcing the wood gas to take a long turbulent path toward the exhaust port.

Sacrificial guard/connector/addaptor tube

The sacrificial guard/connector tube making details are provided in a separate post. The tube shown below is made from the tin plate from a coffee can (Scriber marks can be seen where I marked the metal to get the desired diameter/s.). It’s a quintuple-tricky design that can:

  1. Prevent it from collapsing inwards,
  2. Prevent it from dropping into the stove,
  3. Prevents the stove pipe from dropping over the connector,
  4. Becomes a cheap and easily replaced part that can protect a roll up foil flue pipe from damage,
  5. Lastly, it can be made as an adapter with a taper that allows each end to have a different diameter if required.
A coffee tin that has been cut open to make a sacrificial guard/connector tube to connect the stove pipe for the oil drum stove.
A coffee tin has been cut open to become sheet metal to make a sacrificial guard/connector tube to connect the circular hole in the stovetop to the bottom of the stove pipe for the oil drum tent stove. It will sacrificially protect the stove pipe from heat damage and also can be tapered so that it can fit smaller stove pipes if required.
The oil drum stove viewed from above. The hole on the right is fitted with a stovepipe guard/connector tube made from coffee tin sheet metal. The seam overlap of the tube is interleaved so as to form protrusions that stop it from falling into the stove and at the other end the stove pipe from falling down over the connector.
The oil drum tent stove viewed from above. The hole on the right is fitted with a stovepipe guard/connector tube made from coffee tin sheet metal. It is ready to be fitted with the stove pipe. The seam overlap of the tube is interleaved so as to form protrusions that stop it from falling into the stove. Similarly, at the other end, the stove pipe is stopped from falling down over the connector.

The hand forming of the required curve in such tubes is described in another post (hand-rolling of curves in sheet metal).

Fuel stick/inverted downdraft burner tube

The fuel stick/inverted burner tube can be made using the same method as above using a coffee tin or similar can, if you do not have a welder. The one shown in the two photos below was a welded fule tube. However, I later made one out of a milk powder can and it worked very well. “Even better than the welded one.”

A view looking down on the assembled oil drum stove.
A view looking down on the assembled oil drum tent stove showing the burner tube (left) and the stove pipe connected to the stovetop by a guard/connector tube made for coffee can sheet metal (right).

Performance of the oil drum tent stove

Tent stove combustion

The combustion was hot and clean with no visible smoke from the stove pipe once fully operational (~3 min). It happily burnt damp sticks cleanly and maintained a strong stove pipe draft without sparks. If allowed to run down the stove was a delight to re-start with a few dry twigs and splinters, before solid sticks could be used once more.

Fuel consumption

The fuel consumption was between 800-1600g (28-56 oz) of sticks per hour. This rate depended on stick thickness and fuel loading density. Thin sticks burnt quickly while thick ones burnt much slower. A mixture of stick thicknesses made the stove burn very hot with the least refuelling effort.

The lower fuel consumption rate (~800g/h) was about twice that of my ultralight backpacking tent stoves (~400g/h). An alternative way to look at fuel consumption is that it was between 13-27g/min (0.5-1.0oz/min). I think this really highlights the efficiency of this stove. “So much tent warmth, comfort and cooking are provided from such a tiny amount of wood. What a wonderful free gift of stored energy from our sun.“

The wider fuel port of this stove allowed the use of one or two fat stick to be burnt efficiently with smaller sticks added alongside or preferably in front.

Adding three round fat sticks to ‘fill’ the burner tube resulted in a slow burn that would not be ideal for cooking. However, such a slow burn may be acceptable to keep the winter chill away’ from a tent, but only if the wood was dry. Equivalent sticks when split with sharp corners burnt considerably faster and hotter whether they be wet or dry.

“It was a lazy delight to be able to put a big 1,000mm long stick in and have it burn for ages while supplementing it with few smaller sticks. It also raises the need for a ‘big-stick-stabilizer-ring’, but more on that later as I have ‘lost’ the photo.

The stove does not yet reach the Holey Grail of an all night tent stove. However, it beats the Hell out of fiddly refuelling and frequent trips out into the snow to get more wood!”

Mothy The Elder

Surface temperatures.

For the highest fuel consumption rate (with smaller sticks), the top of the stove maintained a temperature of about 300-400C (572-752F) and occasionally 500C (932) which was very suitable for: body heating, snow melting, boiling water for drinks and simmering dinner.

The fire dome wall was 250-350C (482-662F) which would provide abundant general heating for a small winter tent.

The stove pipe was 62mm dia* 1,500mm long (2.5″*59″) and reached a maximum temperature of about 350C (662F) at the middle of the stove pipe guard/connector tube. At 200mm below the top of the stove pipe (where it may exit through the tent canopy) it reached 170C but generally was considerably lower (~100C). I anticipate that it would be very compatible with my protective sew-on/glue-on DIY soft cotton/silicone rubber stove jacks.

The magic balanced combustion

As a befitting end to this post, the photo below is a peep down inside the nearly empty inverted burner/fuel tube on the tent stove. The fading remnant of the last fuel stick is collapsing into the disappearing charcoal bed.

“It is a wonderful tent stove burner that can consistently burn found wet winter bush fuel sticks. It is remarkable that when doing so, it does not accumulate too much charcoal (charcoal choking).

In addition, it can magically retain just enough charcoal to willingly consumes all wood fuel offered.

It keeps a magical balance between wood and charcoal that is just ‘goldilocks-right’, so long as someone replenishes the sticks. Even if your friends neglect the refuelling for some time (while you rant on about the days skiing exploits), there is plenty of grace time, charcoal and heat to quickly restart the burner. It is not quite as quick as just lighting the gas, but it is almost.

There is no need for air controls, dampers or spark arrestors. Even, your enthusiastic ski friends will not be able, try as they must, to over fuel this stove.”

Mothy The Elder

Even the tiny fading residue of normal combustion shown in the photo below could easily, with care, be recovered to full power within a minute. Dry splinters, followed by twigs, a waxie accelerant or two and the burner will be back at full power and ready for solid fuel sticks.

A view down the inverted burner tube as the remnants of the last fuel stick collapses into the disappearing charcoal bed.
A view down the oil drum tent stoves nearly empty inverted burner/fuel tube. It has the remnants of the last fuel stick collapsing into the disappearing charcoal bed. “This results from a near-perfect balance between the gasification of the wood and the combustion of the resultant charcoal.”

Here is a little Instagram video of the fading embers:

Conclusion

I was delighted with the simplicity and performance of this free tent stove that can be made from rubbish. For winter campers it should provide hours of comfort, cooking and snow melting with very little effort for fuel collection and preparation. A wonderful retreat for enjoying a winter wonderland. The experience may provide the inspiration to make a longer-lasting stove out of more durable materials.

Tim

Addendum

If you have enjoyed this post you may be interested in my other related posts shown below:

Taller stove with side hatch. The next improvement to the stove is a taller stove stand and a ‘turdbuster’ side hatch to allow the addition of big chunks of wood and unwanted alpine body waste.

An improved oil drum tent stove

Biscuit tin tent stove. I also have another post on a similar but smaller free DIY tent stove that is made from a biscuit tin. This may interest you if you are looking for a free tent stove that is more backpackable.

Tent stove from a biscuit tin- a one-weekend-wonder

KISS tent stove. If the drum tent stove is too big and the smaller biscuit tin will not last long enough, then you may be interested in the tiny KISS tent stove that is made of tough stainless steel and is highly backpackable and can be multi-functional for outdoor cooking.

Tent stove- a tiny backpacking stove

Protective stove pipe jack. You may also be interested in a stove jack to protect your tent from the hot flue pipe.

DIY stove jack- Glue-on and sew-on for hot tents
Tent stove- a tiny backpacking stove

2 Comments

  1. Hey Tim,
    Thank you so much for this.
    While some of the pictures/videos are a little bit hard to understand, your text and knowing the concept really helps to figure out what I should do.
    Right now I’m thinking about “how to make a stove pipe but I think I already have some ideas.
    Once again: thank you

    1. Author

      Hi Huck, Thanks for your comments. Sorry if the description is hard to understand. That’s a problem with communication. Regarding the stove pipe, if you don’t want a roll up foil one for backpacking mobility, Just use a piece of scrap pipe.
      Tim

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