Semi-removable inertia mass stove. A mass storage stove or ‘heat storage stove’ is a primary heating device. Its mass, which is made up of heavy material (stone, brick and concrete), stores energy from a fire that burns once during the day (lasting between 1 and 3 hours). Once the fire has gone out, it then continues to give out heat over a prolonged period (for up to 24 hours). Its mass provides thermal inertia which helps to keep an even temperature inside a building (which is why these stoves are often also called “inertia stoves”). The whole of the quantity of wood needed to heat the dwelling is burnt in one go, making it burn hotter which allows complete and more environmentally-friendly combustion. It is a storage device which is designed to absorb the bulk of the energy that is generated from combustion and exhaust gases, which cool down considerably once out of the stove. Accumulated heat is mainly diffused by radiation and, in a few cases, by convection. This particular type of heating, i.e. that uses radiation, is best located in the centre of the dwelling and therefore, most mass stoves these days are positioned in the main room which opens out onto the lounge, dining room and kitchen. As yield tends tend to be in the majority of cases higher than 80%, these stoves are considered to be one of the most efficient wood-fuelled heating devices. Watch the tutorial video here 
The Poelito is a wood-burning inertia stove for small and/or non-fixed dwellings (e.g. motor homes, yurts, caravans, mobile homes, narrow boats etc.). Such dwellings have the following characteristics: - they are less spacious inside and therefore only need a small amount of power to heat. Because of this, a conventional stove is often excessive as it heats the space up too quickly. It therefore needs to burn when it is not giving any real benefit which leads to pollution, soot deposits and poor performance. - Inertia is low which means that there is very little mass that can absorb excess heat and later release it. It therefore gets cold quickly once the source of heat has gone. A storage heater is the perfect answer to these problems.It stores a vast amount of heat and only needs to be burning for 2 hours every 12 to 24 hours; therefore the fire needs to be maintained for less time and heat can be given out over longer periods.
It works on the basis of combining “mass” with “portability”: the sand, which can be easily taken out, provides some of the inertia. If the stove is emptied out then it is easier to move. Whilst in use, the Rocket stove has a vertical feed mechanism which means wood can be supplied to it automatically using gravity. During combustion, the flame is sucked sideways across the bottom which allows air to be supplied from above the fuel. It is an original design guaranteeing efficiency but needs supervision when in use.
This tutorial has been produced by David Mercereau. This is a transcript of work carried out by Vital BIES, who are at the forefront of the idea behind the design of the Poelito and authors of the manual : https://drive.google.com/file/d/1SDJ3YHpDVMU- OoX5gND9xs4qdx8HZaNJ/view. We would like to thank them for the work they have done for our community. Only the construction and operating instructions are included in this tutorial. Additional options are covered in the Vital manual which include the doors providing access for cleaning and adding extra features such as heated seating or a water heater. We will also not be covering the openings from which the sand is removed as this will add to the complexity of building it. The sand can be removed at any time from the top of the stove.
This English translation has been possible thanks to the PerMondo project: Free translation of website and documents for non-profit organisations. A project managed by Mondo Agit. Translator: Gill Barringer. Whilst great efforts have been made to ensure the quality of this translation, the translator makes no guarantees and will accept no liability for any claims made against her in the event of any misinterpretation, errors or omissions thereof.Find in this report an analysis for the use of this poelito, as well as the 11 other low-techs experimented during the project En Quete d'un Habitat Durable (In Search of a Sustainable Habitat)
* Pipework (tubes of differing diameters and T-tube)
Health and Safety:
For the Metalwork:
There are a number of items that are needed to build this stove, which can either be bought from new or salvaged.
NB 1: the 2 pipes that are used for the (fixed) ash tray and the (removable) feed pipe must have a male fitting at one of their ends to accommodate the stopper. NB 2: A rigorous approach must be adopted when producing the exhaust system, using pipes which are compatible with one another. It is important to avoid leaks (condensates as well as smoke) and also the risk of fire .
AVOID making concrete with ordinary cement or ‘black’ cement (unlike fire cement, it does not contain alumina)
The final thing to do for the ‘crash test’ is pour a glass of cold water over it. If there is no reaction, then it is specialist glass. Do not put it on the grass in case it breaks.
In this image, you will find the average supply costs for the different models. Taking the drum and the smoke exhaust out of the equation, the pipework will be a major part of the budget.
The idea behind the Poelito is to build a rocket stove inside a drum. The bottom of the drum is lined with an insulating mix of concrete; however the stove still needs to stand on a fire-proof support.The bottom part of the stove is cast in refractory concrete around a mould made of cardboard tubes. This is the area where the fire develops.Tubes are used to make the hollowed-out conduits: these are the routes which the smoke and fire take. The lower part forms the base of the fire pit and is a fixed body of material. The upper half is made up of removable metal pipes and is filled up with sand. This can either be left standing or transported separately. The fire pit can be closed to the outside either by a cast iron plate or by a pane of ceramic glass which can then be covered over by the drum lid as a finishing touch. The exhaust pipe is on the outside of the drum to which connection is made by a T joint with cap for cleaning out. Any pipes that go along the ceiling and to roof vents (or anything which goes outside of the dwelling) must be insulated.
In the picture, you can see the bottom of the vertical feed pipe and the ash tray at the front and, behind, the pipe where the fire is lit . This together forms the burner. Towards the back, there are 2 pipes where the smoke is forced down. These are situated on either side of the pipe where the fire lit. These pipes join up underneath by means of a manifold which directs the smoke towards the back in the direction of the smoke exhaust which forms the manifold. Connection to the exhaust pipe is by means of a T with cap.
It is possible to make the Poelito in three different sizes which will be depend on the type of dwelling, the space that is to be heated, the exterior temperature and how well the dwelling is insulatedː
It is low power and low mass and is only suitable for small buildings with, at the very least, good insulation. As an example, in a large caravan (7m long), it is OK for temperatures down to 0°C but when the temperature drops to -5°C you cannot expect any more than 12°C in the morning if you lit a fire in the evening. Heavy use of an under-sized stove makes it less durable.The cooking area is fairly small and only allows use of small pans.
This is the best compromise in the terms of bulk v power and transportability. It also is suitable for a studio. It has a good cooking area with the possibility of a water heating option.
This design is most suitable for lightweight dwellings with a floor-space of more than 20 m² or for a solidly-built, moderately insulated dwelling with a floor-space of more than 35 m² .A device which does not need to be moved very often and requires options such as water heating and heated seating would be suitable for this size of dwelling
The authors of this guide and the organisation which makes it available disclaim all liability resulting from the use of the Poelito. You are solely responsible for the implementation of the proposed device. Take precautions, remain calm and composed when in action. Above all, question any so-called “good ideas” you may have (e.g. “that will be OK like that”...).
Safety during construction
Always use safety equipment required for the task undertaken. Metal can be a dangerous material to work with and cement may be toxic if inhaled. Ensure you have an suitable work plan and only use the right tools to assemble pieces when machining (clamp, vice, locking pliers)
Installing the stove
Like all stoves, it is important to respect safety rules in order to not put yourself or your dwelling at risk.
Weight /foundations:This device is of a substantial weight.In a lightweight dwelling, it is imperative that you put something under the floor to withstand the weight and avoid it collapsing. As a minimum, you will need at least a block which stands on the hard surface to sufficiently support the floor. If needed, insert a transverse beam between existing supports (to form a joist) and a block for maximum effect. In conjunction with this, a ground protection mat is recommended as the floor can be relatively flexible and can become distorted in places due to the weight being concentrated in a given area (at points of bearing heavy loads). This means laying any such material on the floor that is sufficiently rigid and of a size to distribute the weight over a larger area than that on which the device normally stands.
Ground Protection: Where appropriate, it needs to be placed on a thick metal plate which is large enough to distribute the weight. If installing the device on top of combustible material e.g. a plank of wood, the device must be lifted up to allow air flow underneath or placed onto an additional mass or thick insulation.
Spacing between walls:The stove must be placed 15 cm minimum away from all walls. If there is less than 45 cm between the stove and nearest wall, it must be protected with fireproof insulation such as rockwool. It must not under any circumstances be in contact with combustible material.
Conduits:The smoke exhaust pipe must comply with current standards. These are basic standards and prevent fire from breaking out in the dwelling. There must be a safe distance of 30cm between any wall made of combustible material and a single-skin pipe. A double-skin pipe is to be used for going up inside the roofing and for outside (with a safe distance of 10 cm for it to go through the roofing). A build-up of heat must be avoided at all costs: the 10 cm collar which goes around the pipe where it goes through the roof should not be left unfilled. It will need to be filled with fire-retardant insulation. The temperature could rise sufficiently to catch fire in an empty space (especially if it is closed off from the outside).
Chimney Height: The layout will have an effect on air circulation. Obstructions which cause air disturbances should be avoided. The smoke exhaust pipe, in particular, must 40cm higher than the top of the roof. For flat roofs, it must be higher than 120 cm (in this case, it must be properly secured). According to standards, the pipe must also be higher than any obstruction which is less than 8m away (e.g. trees)
Choosing a place to put the stove:Where you put the stove will be often dictated by the possible paths in which the smoke ducts in the roof can take. Clearly, you need to take into consideration the layout of the room. Avoid raising the device up too much as the room should be heated at ground level. If it is placed next to a wall, you should not only pay attention to safe distances but also to the accessibility needed for drawing air in to light the fire and for cleaning out.
As part of the process of making the Poelito, you will need to make up concrete. Fire cement is corrosive to the skin and an irritant to the eyes and respiratory tracts: handle using gloves, wear goggles and an anti-dust mask.
You need to make two different mixesː
You can find details below on how to make it and what materials are needed. Reference to this will be made at different times during this tutorial.
How to make up the refractory concrete
How to make up the dense refractory concrete
As with all binding agents which set hydraulically, losing moisture or drying out too quickly inhibits chemical reactions needed for it to set.
It is better to scour down the drum before starting construction.In all cases, this should be done before lighting the first fire as this will blister the paintwork which is not designed for resisting high temperatures. The simplest way to scour it down is by using abrasive discs on a grinding machine. It is also possible to use a sander or attach a wire brush to a drill.
Unless you have a drum with a detachable lid with strapping, you will need to cut the top off of the drum. The top of the drum is used as the cover for the stove once it has been finished. Avoid damaging it and choose the bottom of the drum (which is a complete unit) in preference to the top (which is where the bungs go). This means turning the drum upside down.
Using an angle-grinder and protective gear for hands, eyes and ears, cut just below the rim taking care to not cut the second layer of the metal sheet. That way, the lid can be replaced. A metal saw also works very well. Tip: Start with using an angle grinder (for easiness) and finish with the saw (for precision). Remember to protect the ground with tarpaulin as the remnants of liquid in the drum may leak out from the area you are cutting.
Now that the drum is opened up, it should be cleaned out as it will almost certainly still have remains of oil in it. Use sawdust or sand to get rid of the bulk of the residual oil content. Dispose of the contents as recommended (most likely as toxic waste, you will need to take to a waste disposal site)
Two diametrically opposite holes must be drilled in the drum allowing you to insert the pipes.The front tube (100/130/150 mm in diameter) is to be used as an air inlet and for ash removal.The back tube (80/100/130 mm in diameter) is to be used to connect the smoke exhaust pipe (the respective diameters of PITO model - 60/120/200)
The two tubes should be 6 cm from the bottom of the drum. This is the thickness of the base layer of concrete. When measuring, you need to take into consideration the rim that protrudes beyond the bottom of the drum (If you are filling to 6 cm from the bottom of inside the drum, you then need to add on the thickness of this rim which will be approximately 1.5 cm)
Ash tray side:
Smoke Exhaust side:
On the smoke exhaust side, attach a short sleeve with a female fitting in the same way. The female fitting is on the outside.
There is a risk that the moulds (which are to be made next) will be displaced when pouring the concrete. They should be secured down to ensure the dimensions are correct.
The wires need to point to the inside of drum.
This stopper allows you to shut off the ash tray and regulate primary air intake.
The system of controlling primary air (in the ash tray) should be rigorous and efficient.This allows you to control the power from combustion.
The bottom of the stove consists of 2 different layers: 3 cm insulating mix then 3cm dense mix. The purpose of this is to insulate the bottom of the barrel to protect the ground from heat.
Tip: Once the mixture has started to set, scarify the surface of the concrete in order that the second layer sticks to it well.
You will need to make the moulds so that you can pour the refractory concrete. This is effectively making the conduits where heat and gases circulate. For this, you will need to make moulds for the different conduits using cardboard which then need be taken out after the concrete has been cast. They need to be made solid enough to withstand the pressure of the concrete but equally be easy as possible to take out once it has all dried.
The minimum thickness for the concrete must be 3 cm between the various components themselves and between the components and the barrel. There is a risk that the concrete might crack underneath making the stove not very durable. There is also a danger of the smoke circulating poorly which means the stove will not work very effectively. That needs to be borne in mind when making the moulds, especially when they are positioned in the concrete when casting the mix .
Be careful to ensure the junctions are well covered so that the concrete does not soak into the tubes.
TIP: For connection with the ash tray or smoke exhaust, narrow the gaps with another bit of rigid cardboard. Remove a strip in order to reduce the diameter so that you can slot it into the cardboard mould. TIP: Allow for a 2 cm margin in height so that you have something to get hold of when taking out the castings. TIP: Once the manifold and the horizontal tube where the fire is lit has been completed (these are the hardest to remove), it is possible to cut them longitudinally into 2 or 3 pieces and put them back together. This will make it easier to remove.
Once the cardboard castings have been finished and encased, they need to be placed in the barrel and fastened.
Do the same with the ash tray mould.
Removing the moulds can be done 12 hours after pouring the concrete. This can be quite a tedious task.
The length of the wood feed must be adjusted so that its upper end goes through the lid and you can fit a stopper onto it. However, it must be as short as possible as the draught effect produced when lit works against the outlet line. The shorter it is, the easier it is to light.
It is the same process for the feed pipe as it would be for the ash tray but without adding the air inlet.
To adjust the secondary air flow, all you need is to put the lid half-on. The lid will never be totally closed down during use. At the end of use, the lid is to be closed. This stops the hot stove from sucking in air into the unit, warming it up and escaping out.
he system works even better with a grate fitted to the fire pit and with primary air coming in underneath (onto the ashtray). This allows the embers to keep reducing down as you refuel.
ut the drain grate into a tongue shape so that it can be positioned mid-way up the height of the ash tray, It needs to go just at the back of the fire pit to stop the embers from falling out.
To make this tube out of concrete, you need to make a mould using 2 cardboard tubes, one inside the other. The diameter of the inside tube should match the mould (100/100/80). The diameter of the outside tube must be approximately 6cm larger than the inside one in for the thickness of the tube to be 3cm. This will need to be 2 to 3cm shorter than the bell chamber in order to leave a space under the glass so that the smoke can circulate.
TIP:If you don’t have any cardboard tubes of the right diameter, you can make them by rolling up cardboard. Roll it up with the flutes going vertically.
ALTERNATIVE : For the PITO60, it is possible to make a mould made out of the insulating mix or, alternatively, cut out a tube from thick metal, for example a fire extinguisher (not if made of aluminium) since the gap is very narrow.
The glass should cover the whole of the bell chamber.Before cutting it, check the sides on the Poelito. It is important to make sure that the template is the right size.
Ceramic glass should be used as it is resistant to high temperatures. See Step 1 - Provision of Materials
If you buy this in a DIY shop (€/400 - 700€/M²), get it cut on the premises (TEMPLATES)
The lid closes off the top of the Poelito. It does not have any particular purpose in the system.
ou have now finished making the stove. Before installing it in your future dwelling, it would a good idea to paint it.
The stove is now complete. It is now time to take it out of the workshop to find it a place to keep it long term to get the benefit of it during the long winter nights.
Take care to respect Health and Safety rules in Step 4
Once the device has been installed in the correct position, onto an appropriate base and with the pipe fitted onto it, you now need to put the bell chamber and the feed pipe in place.
Put the lid on the top to check the alignments.
Use the fins to adjust (fold back to straighten them up if they are a bit skewed)
Clay mortar: clay soil (which is sticky) and sand in variable proportions. Generally, 1 part clay to 3 to 5 parts sand, with enough water to make balls that hold and stick . If it is used for sealing or as masonry, it is best to ensure you have the right proportions. However, in this case, this is not important.
Place the glass on the bell chamber without sealing it.
Add more sand as necessary.
Wood must be bone-dry. If not, the stove will not heat up properly and will get clogged up. You need 2 types of fuel:
If 10 to 15cm sections of the wood feed pipe (according to the model) are filled with one big log, then it will not burn very well at all. You need wood of varying and complementary sizes for filling up the conduit properly. Twisted wood is not the ideal for fuelling and should therefore be arranged in such a way that the twigs overlap where they are twisted. Avoid having differing lengths; otherwise, any fuel will do as long at it is wood that is bone-dry.
Put the following into the feed pipe via the opening at the top in the following order:
Once the fuel used for fire-lighting has been well set alight, add enough wood from the top to fill up the whole of the feed pipe without cramming it in. These are the right conditions for the wood to burn properly: combustion is better if the whole of the pipe is filled. The fire develops best in the fire zone and not so well in the feed pipe.
Take care to not constrict the wood too much and it needs to fall naturally whilst it is burning.
Check periodically that the wood is only burning in the bottom part and is getting stuck.Shake the wood up to move it down the pipe if needed. Controlling the draught: it is necessary to retain a small opening on the ash tray to prevent the embers from building up. If this opening is too big, the fire can become wild to the point of rising up and smoking from above. The important thing is that the air should come in from the top of the feed pipe: reduce by a half maximum but never any more than that ǃ
If the glass goes black, one of three thing are wrong: the wood is not dry, it is burning too intensely (too much air in the ashtray), there is not enough air supply from the top.
<u>ATTENTION : </u> During burning, the device requires little surveillance and maintenance.However, with very long pieces of wood, the flames can go up the feed pipe and become wild, especially with softwood. If this is the case, squirt some water in the wood feed pipe to dampen it.
The only maintenance you need to do is to empty out the ashes. If the there is too much ash, then there will be a build-up of embers up to the point that it will clog up the lateral draught towards the area where the flames are: this will mean that it will stop suddenly after a good smoking!
Yearly maintenance. The law states that all users of wood stoves must clean out the flue twice a year, on one of these occasions, the stove must be burning. Clean out this pipe using a nylon brush with a diameter appropriate to the cleaning out cap. Push it up to the top and then back down again. If you do this whilst the stove is still hot, the draught will push the dust out the top rather than come down into the dwelling. It is also important to empty the deposits of ash which are produced at the bottom of the fire and especially at the back of the manifold. This is where it is the ash tends to fly around before being deposited. This is why is it useful to have the door providing access for cleaning opposite the manifold.
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As all the work of the Low-tech Lab, this tutorial is participative, do not hesitate to add the modifications which seem important to you, and to share your achievements in comments.
- More information on the use of poelito and other solutions on David's website :
- Super retour d'expérience sur la construction et l'utilisation du poêlito de Jacob Karhu: https://www.youtube.com/watch?v=ltxlY5X3hRk