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In recent years, more and more chimneys are made from sandwich pipes. The point is a relatively low price, long service life, quite attractive appearance. It is also important that self-assembly of a sandwich chimney is possible. This is not a very simple matter – there are many nuances, but you can do it yourself, without involving specialists.
What is a sandwich pipe and what are they
The sandwich pipe was named so for its multi-layeredness: there are two layers of metal, between which there is a heater. Such a structure solves many of the problems that were inherent in a simple metal pipe chimney. Firstly, the insulation layer does not allow the outer metal casing to heat up to critical temperatures, there is no hard radiation from the pipe. More comfortable conditions are created in the room. Secondly, the same insulation significantly reduces the amount of condensate that forms when the pipe is brought outside. Thirdly, since the outer casing is no longer so hot, it is easier to make the chimney pass through the roof or wall.
What materials are they made from
Sandwich pipes are made of galvanized or stainless steel. Galvanized sandwich pipes for chimneys are rarely used. Unless for the removal of combustion products of a low-power wall-mounted gas boiler or gas water heater. Can be used for insulated ventilation. For more serious heating appliances, they are unsuitable – at high temperatures, zinc burns out, steel quickly rusts, the chimney becomes unusable.
Sandwich pipes for high temperature flue gases are made of stainless steel. Moreover, stainless steel is used in different grades – from alloys with a low content of alloying metals, to high-alloy heat-resistant. The thickness of the metal can also be different – from 0,5 to 1 mm, as well as the thickness of the insulation – 30 mm, 50 mm and 100 mm. It is clear that the scope will be different, and the price too.
The main steel grades that are used in the production of sandwich pipes for chimneys, their purpose and main characteristics are summarized in the table.
| Stainless steel grade | Main characteristics | Application area |
|---|---|---|
| AISI 430 | Possesses sufficient resistance to weathering, but does not tolerate high temperatures | Used for outer jackets of sandwich pipes |
| AISI 439 | Contains titanium, which increases resistance to elevated temperatures and aggressive environments. | Suitable for gas boilers, low-power solid fuel units (up to 30 kW) |
| AISI 316 | Alloy additives – nickel and molybdenum – give high resistance to acids, increased heat resistance. | Optimal for gas boilers of any type. |
| AISI 304 | Cheaper version of AISI 316 with fewer alloying additions | Economy option for gas boilers of medium and low power |
| AISI 316I, AISI 321 | Withstand temperatures up to 850°C | Can be used for heating solid fuel stoves |
| AISI 310S | Increased heat resistance – up to 1000°C (and price) | For sauna and pyrolysis solid fuel stoves |
As is clear from the table, different grades of stainless steel have different purposes. Cheaper alloys are used for the outer casing, more heat-resistant and expensive – for the inner one. This is necessary to reduce the cost of production, and high resistance to temperatures outside the chimney is not needed. There are even more budget options – the outer casing is made of galvanized steel. Outwardly, these products lose to stainless steel, but they serve normally (with normal insulation and its thickness).
Insulation and its thickness
Between the two layers of metal is a heater. Most often it is stone wool. The thickness of the insulation is from 30 to 100 mm:
- With 30 mm thick insulation, the flue gas temperature must not exceed 250°C. Such temperatures are produced only by gas boilers of small and medium power.
- A 50 mm thick insulation layer can withstand temperatures up to 400°C. Scope – any gas and liquid fuel boilers, wood-fired, provided that the chimney is led outside (through the wall).
- A 100 mm stone wool layer allows it to withstand temperatures up to 850°C. Such a sandwich chimney can be installed on any type of solid fuel boiler, in fireplaces and hearths.
In addition to the thickness of the insulation, it is necessary to pay attention to its brand, or rather, to the temperature range in which it can work. Not all stone wool can withstand temperatures up to 850°C, but only some special brands. If you need a chimney for a solid fuel boiler, you will also have to take into account the heat resistance of the insulation.
Connection types
The elements of a chimney sandwich can be connected to each other in two ways: sockets and corrugated edges. The socket connection assumes the presence of a slightly wider chamfer on one side. With this design, a high degree of tightness of the chimney is achieved. This type of sandwich pipe is well suited for gas boilers where it is important to prevent leakage. There is a minus: installation requires high accuracy.
The corrugated edge of the sandwich allows you to assemble the chimney without problems. The disadvantage of this solution is that a significant amount of high-temperature sealant is required to ensure tightness, and it costs a lot.
It is also worth paying attention to the longitudinal seam. It can be welded or folded. If the seam is welded, it must be made in an argon protective environment (so that alloyed metals do not burn out). It is this type of connection that is required for solid fuel boilers, sauna stoves and fireplaces. For all others, you can use the seam connection.
Mounting methods
There are two ways to bring the chimney outside. The first is to lead the pipe through the wall, and then raise it along the outer wall to the required level. The second is up, through the ceiling and roof. Both of them are imperfect.
If the chimney is outside, due to the temperature difference, condensation actively forms in it. Therefore, a tee with a condensate collector (glass) and a cleaning hole must be installed in the lower part of the chimney. This unit allows you to maintain the chimney without much difficulty: the glass is unscrewed, the condensate is drained. Also, soot is periodically knocked off without problems – a special brush for the chimney can be run through the cleaning hole.
If the chimney will be discharged through the roof, several passage nodes will be needed – according to the number of overlaps. If the house is one-story, you will need one passage through the ceiling, and the second through the roof. You will also need a master flash or apron for a round galvanized pipe.
Installation of a sandwich chimney on the street requires only one pass-through node – through the wall. But it will be necessary to fix it to the wall every 1,5-2 meters. If the walls of the building are combustible (wooden house or frame), the walls are necessarily protected by a non-combustible screen.
Smoke or condensation
As mentioned above, one side of the sandwich pipe is slightly wider, the other is slightly narrower. Due to this difference in diameter, the modules are connected to each other. If the wider end is turned up (in the figure on the right), the assembly is called “condensate”. With this method of installation, drops of condensate flow down unhindered. The disadvantage of this method is that with insufficient sealing of the joints, smoke can seep into microcracks. This type of installation of a sandwich chimney is used when the pipe is led through the wall. This is where the free flow of condensate is required, and small smoke leaks are not terrible – they are not critical on the street.
If a narrower edge turns up, the second element is put on top of it with a wider part. This type of assembly is called “smoke” (in the figure on the left). In this case, the condensate flowing down the wall can seep through an insufficiently well sealed joint. But the smoke passes freely. This type of assembly is used if the pipe goes indoors (outputs through the roof). The condensate flowing through the pipe, of course, spoils the appearance, but it is not as dangerous as flue gases leaking into the room. Moreover, with good sealing of the joints, condensate will not leak.
In order for the connection of the chimney sandwich modules to be reliable, each of them is usually coated with a heat-resistant sealant, and then tightened with a clamp.
Parameters
Sandwich chimneys are good because they have a modular structure, which allows you to assemble any configuration, with any parameters. Before you go to the store, you need to know the required chimney diameter, pipe height and those additional elements that will be needed.
Chimney diameter
When choosing the diameter of a sandwich pipe, a simple rule applies: it cannot be less than the diameter of the boiler outlet pipe. If your outlet pipe is 120 mm, then the inner diameter of the sandwich should be the same or larger. It may be wider, but less – definitely not, and narrowing cannot be done throughout the chimney. If the chimney is slightly wider than the pipe, an adapter is purchased, which is placed directly on the boiler outlet, and then the working size already goes.
If there is no boiler yet, but you know its power, you can choose a chimney based on these data:
- boiler power up to 3,5 kW – inner diameter of the sandwich – 80 mm;
- from 3,5 kW to 5,2 kW – at least 95 mm;
- more than 5,2 kW – 110 mm and more.
But it’s better to buy (or at least choose) a boiler, and then decide on a chimney, because many manufacturers insure themselves by making outlet pipes wider to improve traction.
Pipe height
The height of the chimney above the roof surface depends on the place of its output, but at the same time its minimum height should be 5 m. That is, if the height of the house is small, in any case, bring the pipe to a height of 5 meters. If the height of the house is higher than 5 m, then the pipe should rise above the roofing material to the following height:
- Should rise above the ridge by 50 cm if it comes out at a distance of less than 150 cm from it.
- If the distance from the ridge to the pipe is more than 300 cm, then the pipe may be lower than the level of the ridge, but the angle should not exceed 10° (see figure).
- If the chimney exits at a distance of 150 to 300 cm from the ridge, its height may be at the same level as the ridge element or higher.
Under such conditions, normal traction is provided. The smoke will normally go away regardless of weather conditions. To prevent leaves from entering the chimney, they put special umbrellas, weather vanes, and in windy places – deflectors that further improve traction.
If it is not possible to bring the pipe to such a height, they put a smoke exhauster – forced draft is obtained. The fan will not be needed all the time, but in some conditions, when natural draft is not enough, a forced draft saves the situation.
Installation of a sandwich chimney through the wall
There are two ways to lead a smoke tube through a wall. The first option (in the photo on the left) is to raise it indoors closer to the ceiling, and bring it out there. The second is to draw a conclusion at the level of the flue pipe from the boiler. In this case, almost the entire chimney is on the street.
The second option is preferable – it has only one knee, which means that, under equal conditions, traction will be better. Also, with this structure, there is less chance of the formation of soot plugs.
If the flue outlet is not at the back of the stove, but at the top, the installation scheme changes slightly – a 90 ° elbow is added, then a straight section for passing through the wall, and then the same as in other schemes.
The stove itself is placed on a non-combustible base, the wall behind the stove is closed with a non-combustible screen. The easiest way is to fix a sheet of metal on the wall. You can mount on ceramic insulators 2,5-3 cm in height. There will be a layer of air between the sheet of metal and the wall, so the wall will be safe. The second option is to place heat-insulating material under the metal – for example, mineral wool cardboard. Another option is an asbestos sheet (as in the photo).
A hole is made in the wall. Its dimensions are determined by SNiP – the distance from the pipe to non-combustible walls must be at least 250 mm on all sides, and to combustible – 450 mm. It turns out a solid hole, especially when it comes to walls made of combustible materials. There is one point with which you can reduce the size of the hole for the passage of the sandwich: make the dimensions according to the norms of non-combustible walls and sheathe the opening with non-combustible material.
The opening can be round or square, as long as fire safety standards are maintained. It is easier to make and sheathe square holes, therefore they are more often made.
A passage assembly is inserted into this hole – a box made of non-combustible material. A sandwich chimney pipe is inserted into it, fixed in the center. All gaps are laid with heat-resistant insulation, the hole is closed on both sides with non-combustible material. Usually it is a sheet of metal.
One important point: it is necessary to develop a chimney so that there is no junction of two pipes inside the wall. All joints must be visible and serviceable.
Next, you need to make or install a ready-made support bracket that will support the entire weight of the pipe. The design may differ in details, but the main idea is the same – a support platform, which, with the help of stops, transfers weight to the wall.
A similar design can be welded from a profile pipe of a small section of 25 * 25 mm or 25 * 40 mm.
As you can see, a tee is connected to the pipe that runs through the wall. At the bottom there is a removable glass in which condensate accumulates. Some models have a fitting with a small tap at the bottom. This is even more convenient – you don’t need to remove the glass, you can connect a hose to the fitting, bring it into some kind of container (it is very toxic, so you don’t need to drain it near the house) and drain it by simply turning the tap.
Next, the tuba is brought to the required level. Since in this case the distance to the ridge will obviously be more than 3 m, it is possible that the height of the chimney be slightly lower than the ridge – not lower than 10 ° in relation to the horizontal line drawn from the level of the ridge.
But since this house is located in a lowland, to ensure traction, the pipe was raised even higher than the ridge. It was fastened to the wall with stainless steel clamps, with a step of a little more than a meter. On the roof there are stretch marks made of a steel bar with a diameter of 6 mm. To install stretch marks, there are special clamps “with ears” to which stretch marks are attached.
Another important point that many people forget about: at the place where the pipe is installed, on the roof, you need to install a snow retainer section, otherwise, in the spring, the pipe can be blown away with snow (if the pipe is not brought out towards the gable, as in the photo).
How to install a chimney through the roof
When removing the chimney from the sandwich pipes through the roof, it is necessary to take into account the location of the floor beams and rafter legs on the roof. It is necessary to guess so that the pipe passes between these elements. The minimum distance from the outer wall of the pipe to the fuel element must be at least 13 cm, and this is provided that the fuel element is protected by insulation. To meet this requirement, the pipe often has to be moved. Do this using two 45° angles.
Please note that the installation of a sandwich chimney from a solid fuel boiler begins with a metal pipe without insulation. She is black in the photo above. After it, an adapter is placed on a sandwich, and a chimney with insulation enters the passage unit.
A hole is cut in the ceiling that meets fire regulations – 250 mm from the edge of the pipe, if the ceiling is protected by heat-insulating material. Having cut a hole, its edges are covered with non-combustible heat-insulating material. Minerite is best suited for this (nailed or fastened with wood screws).
A chimney sandwich pipe is inserted into the resulting box. It should be directed strictly vertically, without the slightest deviation. You can’t fix it rigidly, you can only give direction by installing a few slats that will hold it, but it can move up / down without difficulty. This is necessary, since when heated, its length increases significantly.
The remaining space is filled with basalt wool (check the temperature range). Another option is to pour expanded clay, granular foamed glass. Previously, sand was still covered, but sooner or later, it all woke up through the cracks, so now this option is unpopular. On the front side, all this “beauty” is covered with a stainless steel sheet, under which non-combustible material is placed (between it and the ceiling). Previously, it was asbestos sheet, but since asbestos was recognized as a carcinogen, mineral wool cardboard was used.
There is one more option. Beat the edges of the hole with mineral wool, and then insert the finished stainless steel ceiling-through unit. It immediately has both a box and a decorative stainless screen.
Having brought the pipe to the attic, they make a hole in the roofing pie. All films at the passage point (vapor barrier and waterproofing) are cut crosswise. The resulting triangles are wrapped and secured with staples from a stapler. So the damage is minimal. The exposed crate is cut so that there is at least 13 cm to the pipe.
In the right photo above, the passage through the roof is incorrect – the distance between the pipe and the boards is too small. In a good way, it is necessary to cut them according to the standard, beat them with the same mineralite. You should get something similar to the following photo.
Further, after laying the roofing material, a master flush is put on the pipe, the skirt is given the desired shape (under the shape of the roofing material).
The junction of rubber and pipe is sealed with a heat-resistant sealant. The roof surface under the “skirt” is also coated with a sealant.
Please note that each connection of the sandwich modules is tightened with a clamp. This is also true for the internal chimney.