Sandwich tube furnace

Despite the wide range of modern heating appliances and modern heating systems, solid fuel furnaces are not going to take their position in popularity.This is understandable - the existence of such heating installations gives a certain feeling of autonomy - even under the most adverse circumstances caused by the intermittent supply of other energy sources, stove with fuel reserve and will help warm the house, and prepare food for the family.

But the furnace will work efficiently and with proper security level only if it is designed, composed and manufactured in compliance with all necessary requirements.And one of the key conditions for the furnace operation is robust and reliable system for exhaust gas - chimney.There are several variants of the equipment of the system - by putting some classical pipe "in the old" brick, before the application of a completely new, sometimes unexpected technological solutions with the use of advanced composite materials.And at the peak of popularity in this issue of our time, perhaps, are the sandwich pipes for furnaces.

what a sandwich pipes for furnaces, how they differ, you need to know about their choices and the basic rules of the system design - all this in this publication.

what a sandwich pipes and their main advantages

Developers sandwich chimney aims to minimize the drawbacks typical of almost all chimneys, regardless of the material of manufacture.

Any flue pipe exposed to the negative destructive influence both inside and outside.The products of combustion are very high temperature and aggressive chemical composition, which leads to erosion or corrosion of the lining material channel.In addition, the flue duct eventually overgrown with soot, reducing the permeability of the pipe, and in the end - the effectiveness and safety of the oven.

outside in the open areas of the pipe are external factors - humidity, precipitation, air temperature fluctuations on the street.In addition, the temperature difference between the outside and inside of the chimney leads to the active formation of condensate - and this, in turn, increases the likelihood of taxation Sazhnev growths.

«Classic» brick chimneys, although considered to be time-tested, have a whole "bouquet" of the shortcomings.

• Firstly, a rectangular section of the channel is by no means the best - it will inevitably occur unnecessary turbulence of the gas flow.Reduces the overall traction.
• Secondly, it is impossible to achieve perfect smoothness of the channel walls - porous structure of bricks still will promote sooty deposits.
• Thirdly, on its own brick chimney is a very massive structure, a rather complex in construction and require a reliable basis.

As laid brick chimney

If you chose this option, a number of important rules must be strictly observed.For information on how to fold a brick chimney in the home - in a special publication of our portal.

• And fourth, even high-quality brick on the influence of a complex of negative influences defeated erosion and crumbling chimneys picture - not a rarity.

means that the chimney is optimal, it must make a circular section, smooth inner walls of a heat resistant, resistant to corrosion and erosion of material.and light enough so as not to burden the design of the whole furnace.It would seem that all these requirements are met by modern types of stainless steels.However, this simplified scheme is not possible for several reasons:

• Any metal has a high thermal conductivity and high temperature difference inside the flue duct and the outside can be damaging act on the thin walls, and most importantly, results in an abundant condensed water vapor always containedin the composition of the combustion products.
• rapid cooling of the gases in the open areas of the chimney will inevitably reduce the furnace draft.
• portion of the metal pipe, located inside the building, heated to very high temperatures, and it is not safe and the fire point of view, and from the standpoint of the high probability of accidental injuries - burns.

This complex problems entirely or to the greatest extent possible, be allowed the creation of sandwich construction chimney.The inner channel and the outer surface of this design consists of two separate metal cylinder, separated by a layer of heat-resistant thermal insulation mater, has a pronounced low thermal conductivity.

internal channel should always be executed in stainless steel special type, with robust provarkoy seam - is commonly used argon welding.

outer casing - also metal, but there is already possible options.Of course, the most resistant to external influences will be the cover of stainless steel.However, sometimes in order to save and acquire the cheaper options in which the outer pipe is made of galvanized steel.

as thermal insulating layer is most commonly used mineral wool from basalt fiber as most resistant to high temperatures.The high density of basalt wool (120 to 200 kg / m³) provides the necessary structural strength.The thickness of this layer may vary - and even from 25 to 100 mm.It depends on the settings of the heating equipment, and to a certain extent, on the climatic conditions of the region.

more amenities such design that it carefully considered the questions of installation of individual parts in a single system.For this the connecting nodes in the form of sockets and narrowed sections, special clamps, stoppers, sometimes - flanges, etc.

This chimney system for the furnace immediately acquire a number of important advantages :

• Massa entire chimney system assembly - is not so great, that is, do not have to reinforce the foundation of the furnace and its structure, as in the case of the brick chimney.
• flue can be positioned vertically on the bracket along the outer wall of the building.And this - the simplification of the assembly, especially when passing through floors, and a substantial saving valuable space inside the premises.
• system is very "flexible" in terms of its accommodation capacity.Manufacturers provide a wide range of additional parts and components to quickly and reliably collect the necessary configuration of the chimney.There is an opportunity to bypass possible obstacles, without resorting to large-scale alterations house construction.

• temperature difference between inside and outside is compensated thermally insulating layer.This ensures the stability of the normal steady thrust of condensate loss and soot deposits are reduced to a minimum.
• outer surface of the sandwich pipe with proper assembly is not heated to the critical temperature, ie, significantly increases the safety of operation of the chimney.
• Assembling such a chimney in compliance with all recommendations of the technological - an affordable and intuitive exercise that does not require any special training.

have such flues and specific disadvantages :

• quality set will cost quite expensive.
• Over time, under the influence of high and low temperatures at the junctions of the individual components may be signs of decompression - it requires special attention: regular inspections and, if necessary, maintenance.
• limit the total lifetime.Despite the fact that high-quality stainless steel is highly resistant, aging it is also not sidestep.As a rule, manufacturers guarantee up to 15 years of trouble-free operation of its products.However, any other chimney for such period will almost certainly require any repair work.

How to choose metal sandwich chimney

As already mentioned, the cost of a similar chimney system - is quite high, and replacement of defective pipe sections may result in considerable costs.Therefore it is very important to be able to properly evaluate the product in the selection, to the disappointment did not come after one - two years of operation.

selection criteria can be divided into several categories.Thus, in the first evaluation of the quality of the materials used in the manufacture of sandwich pipes.Selects the required linear parameters - that is, the diameter of the chimney duct, the height of the future of the pipe, the thickness of the insulation layer.It is important to immediately consider the design features created to evaluate whether all the components are commercially available for the installation.

Evaluation of the quality of manufacturing materials

inexperienced eye all stainless alloys seem to be the same.New pipe molds brilliantly - but it is not a criterion of quality of the metal.

same "beautiful and brilliant" pipe through the short period of time may be deformed or even simply burn through - alas, considerable evidence on the Internet.A similar situation - a direct route to a fire or carbon monoxide poisoning.

Unfortunately, it must be noted that the increased demand for these chimneys and spawned the "shadow sector" of their production, which uses materials unsuitable for such purposes.It happens, and the situation is different when it is a high quality sandwich was used in conditions for which it is simply not designed.For example, a pipe, which is quite suitable for the gas boiler is not suitable for use with solid-fuel stove.

Brand stainless steel

Choosing sandwich pipe, it is necessary to focus on the steel grade, which is used primarily for the domestic channel.This option must be specified in the passport product documentation, of course, if it is issued in good faith by the manufacturer.If the steel grade is not specified, it is better to look for another option.

So, can meet the following grades of stainless steel:

- AISI 430 .This steel belongs to the category of the most inexpensive.It is quite suitable for the external cladding of the sandwich, as its resistance to weathering - is enough.But for the inner tube, it does not fit categorically.Its composition determines the weldability unimportant, that is, to get an airtight seal - is very problematic.No reply this steel and the requirements of raised temperature resistance.

- AISI 439 .This titanium alloy is enriched with additives, which significantly enhances its corrosion resistance and mechanical strength.of such steel pipes are well suited for any gas installations as well as solid fuel boilers and furnaces, but only a small heat capacity.

- AISI 316 .In this steel pronounced corrosion resistance to virtually all aggressive substances.Temperature resistance - the average, so the tube is suitable only for equipment operating on gas.

- AISI 304 .Steel is not the highest heat resistance performance, so the use is not normally used in an internal passage at the major manufacturers.For the outer casing fits perfectly.

- AISI 321 and AISI 316 i .Has excellent heat resistance and good plasticity, easy to high-quality welding.Such pipes are quite suitable for most types of furnace and boiler equipment since withstand without deformation heating to 850 ° C.

- AISI 310 S. Fully versatile steel, can withstand temperatures up to 1000 ° C.It is even suitable for high-power solid-fuel stoves and boilers, working on the principle of afterburning pyrolysis gases.The only conventional drawback - the high price.

sovey Knowing the parameters of the furnace, it is possible to choose the optimal brand and stainless steel.

Do not forget about one more way to stainless steel testing.Of course, he does not give an accurate picture, but it will just avoid buying poor-quality fakes:

necessary to take an ordinary magnet and try to "paste" it to the inner wall of the vertically standing sandwich pipes.The magnet should not be kept - ideally he just soskolznёt down.If he stayed on the spot or coming down with a visible deceleration - "black" became a component is too high, and the pipe is not suitable for the chimney.

type of insulating material

As already noted, as insulation material for the thermal insulating layer to be used exclusively basalt rock wool.No way, whatever seemed attractive price, do not buy a sandwich with a filling tube of glass.Thermal conductivity of glass wool have not worse, the heat resistance - is quite different.At temperatures of about 300 ° C begins its sintering, subsidence in size, and all of its advantages are reduced to zero.In addition, fiberglass - very brittle, and warming layer is different volumetric stability, prone to shrinkage.

In really high-quality sandwich pipe manufacturers are using insulation leading brands - ROCKWOOL, PAROC and the like.

diameter chimney channel and the thickness of the insulation

Manufacturers provide a sufficiently broad range of diameters sandwich pipes.Thus, the pattern produced by the inner tube 110 and up to 300 mm, with varying thickness of insulating layer that is different external diameter design.

If purchased new equipment, boiler or furnace, the passport data must indicate the required diameter of the chimney - this value and should be followed.It is more difficult if the chimney is planned to be installed in a brick oven or homemade metlalicheskuyu - it is important not to make a mistake with this parameter.

In this case, we can proceed in several ways.First, a simple - to navigate in the table showing the dependence of thermal power equipment and flue diameter.

Thermal power solid-fuel furnace	Minimum cross-section of a rectangular chimney	cross-sectional area of ​​the pipe	minimum diameter of the inner tube sandwich chimney
kW	kcal / h
to 3,5	3000	140 × 140 mm	19600 mm²	158 mm
3,6 ÷ 5,2	3000 ÷ 4500	140 × 200 mm	28000 mm²	189 mm
5,3 ÷ 7,0	4500 ÷ 6000	140 × 270 mm	37800 mm²	220 mm

can navigate and an exemplary flow of the existing furnaceor other fuels.