DIY masonry stoves: how to build them? Project and advice.
How to build a masonry wood stove? Let's see how to make a healthy and healthy heating source that does not create impact and environmental pollution
What is a masonry stove?
The masonry stove is an apparatus used to heat indoor environments, which produces heat by burning 1/3 wood charges in a day in a combustion chamber, closed and inside the stove. The heat accumulates in a substantial mass of refractory material, with which it is made, and is slowly transferred to the surrounding environment, heating people and objects in a constant, uniform manner over long periods of time.The masonry stove has very ancient origins, and today, despite being supplanted by more modern and efficient equipment, it is still very widespread in some areas of northern Italy.The masonry stove is a structure made of materials able to accumulate a large amount of heat which is then slowly transferred to the environment by irradiation ensuring a comfortable and healthy situation.The traditional masonry stoves that are handcrafted in their entirety in the location, can have different shapes and coatings (generally majolica tiles), but have common characteristics:they are all made of refractory material ( refractory bricks, clays, raw earth).characterized by a complex loop of fumes, an articulated path of smoke that optimizes the heat exchange with the refractory material.As for the masonry fireplace, also for the masonry stove, the efficiency of the flue must be important and must be adequately sized to ensure perfect smoke draft and convey it to the outside.
Differences with a common stove.
The definition provided above could lead us to consider the brick stoves very similar to common stoves or the classic open fireplace. In fact, these are also used to heat rooms and can function by burning wood.However, there are substantial differences between these and the brick stoves examine them:Mode of transmission of the produced heat. The common wood-burning stoves are made of materials, such as steel, which is heated immediately reaching high temperatures and just as quickly heats the air in which it is immersed and that comes into contact with it. Air which increases in temperature increases in volume and consequently decreases in density. For this reason it rises up and frees up space in contact with the hot stove. Space that is immediately occupied by cold air. This continuous motion, which is determined, known as convective motion, makes, after some time, that the entire volume of air contained in the environment is heated and brought to a higher temperature. This type of transmission of heat and therefore of heating, which is then the one with which the common stoves work, is known as heat transmission by convention. The storage heaters, and in particular those in masonry, on the other hand, work by transmitting heat with a different mode called irradiation. The storage stoves are constructed using a consistent mass of materials that have great heat storage capacity, which then slowly yield to people and objects contained in the environment in the form of electromagnetic waves with frequency in the infrared. This is precisely the transmission of heat by radiation. Irradiation that heats up without raising the temperature of the room air with a mode that is the same with which the sun heats the earth. The storage stoves are constructed using a consistent mass of materials that have great heat storage capacity, which then slowly yield to people and objects contained in the environment in the form of electromagnetic waves with frequency in the infrared. This is precisely the transmission of heat by radiation. Irradiation that heats up without raising the temperature of the room air with a mode that is the same with which the sun heats the earth. The storage stoves are constructed using a consistent mass of materials that have great heat storage capacity, which then slowly yield to people and objects contained in the environment in the form of electromagnetic waves with frequency in the infrared. This is precisely the transmission of heat by radiation. Irradiation that heats up without raising the temperature of the room air with a mode that is the same with which the sun heats the earth.Combustion efficiency.The combustion efficiency is the parameter that measures the ability of a stove to burn the fuel that feeds it completely and without generating polluting by-products. The thermal energy (heat) that the wood burning is able to produce is attributable for about 30% to the combustion of its solid phase (coal) and for about 70% to the combustion of its gaseous phase (hydrocarbons, hydrogen and carbon monoxide) which is released after an initial distillation process known as pyrolysis. In the simpler models of traditional stoves and open fireplaces this second phase of combustion is not realized because it requires high temperature (above 700 ° C); abundant amount of comburent oxygen (in a ratio of 1: 3 with pyrolysis gases) which must mix with the pyrolysis gases in turbulent conditions. For this reason, in common stoves and fireplaces, a substantial part of the energy that could be made available by the combustion reaction is lost with a drastic reduction in efficiency. In addition to all this there is also the aggravating circumstance of incomplete combustion rich in pollutants. In the masonry stoves, however, the combustion chamber and recirculation of the combustion air are made in such a way as to cause said secondary combustion and maximize efficiency. The comburent is in fact divided into two distinct flows before entering the brazier. A first flow directly feeds, from below, the primary combustion of wood that releases pyrolysis gases. A second flow, on the other hand, runs through the walls of the combustion chamber externally and upwards. Once in its upper part, which is also the hottest, penetrates into it, and invests in reverse current the pyrolysis gases, which have emitted from the wood as a result of the first combustion, igniting them. This triggers the secondary combustion which, by releasing a further substantial amount of heat (about 70%) and reducing pollutants, maximizes thermal efficiency. In summary, therefore, the masonry stoves have a high thermal efficiency while the common metal stoves have a low thermal efficiency.Heating efficiency / heat storage capacity. The heating efficiency measures the speed with which the heat produced is transmitted to the room to be heated. The storage capacity, on the other hand, expresses the stove's ability to accumulate the heat produced. The two parameters are therefore in opposition to an apparatus with a high heating efficiency has low accumulation capacity and vice versa. The majority of common stoves, being in metal, have as already said a high thermal conductivity. For this reason, as soon as the combustion begins, they quickly heat up and reach high temperatures rapidly heating the environment in which they are allocated. But just as rapidly they cool as soon as the combustion ends because the materials they are made of have low heat storage capacity (low mass and low thermal capacity). So if you want to keep a room warm using a common stove it is necessary that this is continuously fed by burning wood. On the other hand, the masonry stoves, on the other hand, have excellent heat storage capacities (high mass and materials with high thermal capacity) and then heat up slowly and with as much slowness start to heat the surrounding environment, but once the burning of the wood charge is finished, they continue to release heat gradually, keeping the room temperature constant for many hours (at least 8) without having to burn more wood. Summing up the masonry stoves, compared to the common stoves, they have low heating efficiency but high storage capacity and therefore very low fuel consumption, which translates into low running costs.
**How to design a masonry stove: **
dimensions and tips.Let us state that an exact theoretical calculation of the characteristic parameters of a masonry stove is anything but simple since they depend on a very large number of variables and can not be reduced to simple mathematical formulas. Fortunately, in the realization of such a task, a series of rules and empirical rules come to the rescue. Rules, still valid today, deduced from the experience of generations of craftsmen who often ignored the physical principles of operation at the base of masonry stoves.
Let's see how we proceed
Collection of data that characterize the environment in which the stove is to be placed.Going into detail you will need to know:Geographical location of the house . It is a general indication of the minimum temperatures that will be touched in winter. Therefore a house in a mountain village in Northern Europe will presumably have to be equipped to allow its inhabitants to survive comfortably at temperatures that will be constantly different degrees below 0 ° C. On the other hand, a house in a mountain village in Italy will have to be equipped to overcome temperatures that more or less stably will be around 0 ° C.Thermal insulation of the house. It is a direct consequence of its constructive realization. It is quite evident, in fact, that a house built with thick walls of insulating materials (stone, solid bricks, raw earth) better retains the warmth of a building with thin walls of perforated bricks.Cubation (volume) of the rooms to be heated. To acquire this data, multiply the surface (square meters) of the room to be heated by the height of the same. More rooms are heated with a masonry stove. To do this, just place the stove on top of the rooms you want to heat up.This information allows choosing the type of masonry stove that must be installed and consequently also its operating characteristics .Usually, in fact, it is used to differentiate the masonry stoves in three different types depending on their weight and therefore the thickness of their walls. According to this criterion we will have:Heavy masonry stoves. They adapt well to very harsh climates such as those of the North of the world or the extreme South with temperatures that constantly stand very degrees below 0 ° C. Given their substantial mass they have great storage capacities and therefore can only be loaded once in 24 hours.Medium-weight masonry stoves. They adapt well to climates whose temperatures oscillate slightly around 0 ° C as can be those of the mountain countries of Italy. Given their small mass they can be fed with two daily charges at 12 hours.Stoves in light masonry . They are suitable for climates that only occasionally reach temperatures close to 0 ° C. So centers of the northern plain of our country. Due to their low mass they require at least 3 daily charges at a distance of 8 hours. For reasons of practicality, light brick stoves can be replaced by cast iron stoves which, despite being made of metal, have good storage capacity.Calculation of the required thermal power.We hypothesize having to design a medium-weight brick stove and therefore having to heat an environment with good thermal insulation (thick walls made of stone, raw earth and bricks) positioned in an apartment located in a mountain village in Italy.
We know from the famous empirical formulas of which it has been mentioned that to heat a volume of 1 m3 (corresponding to a walkable area of 0.4 m2) will require 0.04 KW of thermal power for each hour and a radiant surface (lateral surface of the solid that constitutes the stove) of 0.04 m2. Therefore to accumulate in the mass of the stove the necessary heat to maintain the constant temperature in the time that elapses between two successive charges (12 hours) will be necessary 0,04 X 12 = 0,48 KW.If we assume that the room to be heated has a total volume of 25 m3, 0.48 X 25 = 12 KW will be required.Now, knowing that on average the combustion of a Kg of dry wood, seasoned 2 years, develops a thermal power equal to 4 KW, it is assumed that to heat our room for 12 hours it will be necessary to burn in a stove load 3 kg of wood. This number should however be increased by about 30% to take into account the heat that is lost in the exhaust fumes that will come out of the chimney with a temperature that is just under 200 ° C.By updating our calculations with this corrective factor we will obtain that the weight of the wood to be used in each combustion will be equal to about 4 Kg.Sizing of the combustion chamber.To proceed in this way, suppose again that the wood is cut into rods with a height of 20 centimeters and that they are placed standing in the burner (vertically). This therefore can be assimilated to a parallelepiped which will have a height equal to 20 cm.It is known that a volume of 2,000 cubic centimeters of wood weighs one kg, so 4 kg will occupy a volume of 8000 cubic centimeters. Always in the hypothesis that the rods are contained in the parallepipedo described above this must have a base area equal to its volume divided by its height and then 8000/20 = 400 square centimeters.Therefore the base surface of the burner must be at least 400cm2. Surface that can be made in a rectangular shape but better still in a square shape. A rectangle, in fact, has diagonals longer than a square of the same surface and therefore angles more distant from the crossing of the diagonals. Condition that worsens combustion efficiency. All this because the corners away from the center have lower temperatures than average and this causes turbulence that damages the combustion efficiency. In order to allow, during the combustion, to the flame that emanates from the rods at the feet not to break and not to touch the roof of the brazier it will be necessary to calculate for it a height that is at least equal to the height of the rods plus another 40 cm . So at the endthe fireplace must contain a volume of at least 400 cm2 x 60 cm.The realization of the fireplace must also contemplate a series of openings and precisely:a first opening from which the serpentine of the smoke ride begins;of the inputs for the two flows of combustion air, one on the perimeter at the base of the hearth to feed the primary combustion and one, or better still more than one, on the perimeter at the top after covering a gap that surrounds the chamber itself.The surface of the starting hole of the flue gas must be a multiple of the total surface of the sections of the holes which add the combustion air. And precisely it must be about 9 times the surface of the holes that add up air. Furthermore, the opening of the fumes rotation must be positioned on the wall opposite to those of the combustion air inlets. All this in order to avoid turbulence in the combustion chamber which would lower the combustion efficiency.Calculation of the mass of the stove.The mass of the stove must be directly proportional to the power that it produces with combustion at a rate of 1 kg for each 0,004 KW it will have to develop. And so to get 12 KW the stove will have to weigh 12 / 0,004 = 3000 kg.Sizing of the smoke ride.The dimensioning of the flue gas cycle depends on the characteristics of the flue and, in particular, on its draft and again on the power of the stove. With more precision for each KW / h we need 1 meter / 1 and a half meters of fume length (1 m if the draft is large, 1,5 m if it is normal). Where the draft is a phenomenon of natural ventilation caused by the convective motions of hot fumes that tend to rise by sucking those at a lower temperature.
The section of the coil with which the smoke is made is not constant and decreases as you approach the entrance to the chimney.This is because initially the fumes are hot and will have a greater volume, but, progressing along the path to which they are obliged, give off heat, their temperature is lowered and therefore their volume also decreases and consequently will have to decrease the section of the conduit. To get an idea of the extent of how these dimensions vary and how they depend on the power of the stove, we specify that for each Kw / h of power a section is necessary that initially must have a surface of about 120 cm2. Said surface progressively, and possibly in a constant manner, must decrease as the conduit progresses until it reaches 85 cm2 at the entrance to the chimney. It would be a good idea to shape the flue gas so as to have a square section possibly with rounded corners (in order to minimize the turbulence that creates condensation). If all this is not possible and it is necessary to shape the coil so that it has a rectangular section, the ratio between the sides must not be greater than 2/1. It is good practice to foresee a variable thickness of the walls that will enclose the fumes. All this to ensure a uniform heat radiation as the temperature of the fumes, and therefore the radiated heat, decreases as they approach the chimney. Therefore, the coil coating must be more often near the brazier and progressively decrease as you approach the chimney. If all this is not possible and it is necessary to shape the coil so that it has a rectangular section, the ratio between the sides must not be greater than 2/1. It is good practice to foresee a variable thickness of the walls that will enclose the fumes. All this to ensure a uniform heat radiation as the temperature of the fumes, and therefore the radiated heat, decreases as they approach the chimney. Therefore, the coil coating must be more often near the brazier and progressively decrease as you approach the chimney. If all this is not possible and it is necessary to shape the coil so that it has a rectangular section, the ratio between the sides must not be greater than 2/1. It is good practice to foresee a variable thickness of the walls that will enclose the fumes. All this to ensure a uniform heat radiation as the temperature of the fumes, and therefore the radiated heat, decreases as they approach the chimney. Therefore, the coil coating must be more often near the brazier and progressively decrease as you approach the chimney. It is good practice to foresee a variable thickness of the walls that will enclose the fumes. All this to ensure a uniform heat radiation as the temperature of the fumes, and therefore the radiated heat, decreases as they approach the chimney. Therefore, the coil coating must be more often near the brazier and progressively decrease as you approach the chimney. It is good practice to foresee a variable thickness of the walls that will enclose the fumes. All this to ensure a uniform heat radiation as the temperature of the fumes, and therefore the radiated heat, decreases as they approach the chimney. Therefore, the coil coating must be more often near the brazier and progressively decrease as you approach the chimney.How to build a masonry stove?As mentioned several times, the construction of a masonry stove is a complex matter and requires skills and experience, both design and construction skills. In some regions of the world such as Patagonia Argentina, the State, in order to encourage this type of heating that is environmentally friendly and does not consume fossil fuels, provides interested citizens with a kind of kit with: material needed, design drawings and precise and detailed instructions. In our country this opportunity does not exist even if in different mountain villages, in the context of a more general project of recovery of ancient traditions that are getting lost, there are organized courses for cars to build masonry stoves. Anyway, in the following we provide aoutline of the operative procedure to try to complete such a work .
Materials and tools needed.
Refractory bricks or alternatively, if you want to make a construction in total respect of nature, self built earth bricks.
o make these bricks we need to dig a hole at least one meter deep and obtain the earth from it, which in this way will be free of impurities of organic origin. The earth thus collected is kneaded with water and then with the mixture and a mold the bricks of dimensions of 15 x 30 x 5 cm are formed which will be dried in the sun. If the soil available has a low clay content, the brick drying could crack. This problem can be remedied by adding to the dough shredded dough.Refractory cement. Cements that resist high temperatures and the mechanical stresses caused by temperature changes contain high percentages of silicon and aluminum oxides and calcium aluminates.SandMetal door and relative frame to close the combustion chamber loading compartment.Raw earth, or earth rich in clay left to dry in the air.Refractory plaster that resists high temperatures.Straw.Insulated steel pipes for the chimney.
Required tools.
Meter.
Team.
Level.
Cardarella.
Trowel.
Staggia,
aluminum bar of different length.
Plaster trowel.
Summary description of how to proceed.
The construction of a traditional solid brick stove provides the following steps:Construction of the base.Construction of the combustion chamber with smoke turns.Coating.Base construction:We start by creating the base on which the stove will develop . In any case, given the high weight of the apparatus, it is good practice to have the floor examined by a structuralist and possibly make the suggested changes. The first step is a platform made with cement mortar about ten centimeters high and with a surface that satisfactorily contains the hearth whose dimensions have already been calculated and any annexes that make up the departure of the fumes ride.Around this initial platform is created a frame, with bricks side by side, about twenty centimeters high creating a sort of pool that is filled with a layer of raw earth mixed with straw.On this layer there is a pouring of cement mixed with leveling sand.Construction of the combustion chamber with smoke turnsHaving created the platform that has the function of thermal insulation , the combustion chamber of the established measures is built on it, with bricks, taking care to give it a square plan and to round off the edges with pieces of bricks.In the combustion chamber are made holes for the primary and secondary air inlet , the starting point of the fumes and the compartment in which the wood loading door will be mounted.Then the fumes are built, always with the bricks in raw earth, adapting as much as possible to the criteria that have been described and to a rough design that has been realized and designed before starting with the operational phase.Along the route of the smoke ride , some openings will be left which will close with removable plugs and which will be used for cleaning operations that must be carried out periodically.coatingOnce realized , the artifact will be covered with a layer of bricks and then plastered to shape its final shape.The final plastering can be raw based on lime or covering the plaster with lava stone or soapstone, or you can cover the stove with majolica tiles or ceramic tiles.