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The chimney is one of the most important parts in the design of a boiler house based on any fuel-burning boilers, including condensing ones. Proper design, material selection and quality installation chimney - the necessary conditions long and efficient operation of the boiler house as a whole.

The main feature of flue gases from condensing boilers is their low temperature compared to flue gases from conventional boilers. In turn, the low temperature leads to the mandatory formation of a certain amount of condensate in the chimney. It is these two factors - low temperature and condensation - that are decisive when choosing a chimney material for a condensing boiler. In addition, the need to ensure a permanent removal of condensed moisture must be taken into account in the design and geometry of the chimneys.

Against the background of the above, we will analyze three main aspects regarding chimneys for condensing boilers:

  1. Materials used;
  2. Design features;
  3. Basic installation schemes.

Materials for the manufacture of chimneys for condensing boilers

The two most common materials used for condensing boiler chimneys are flame retardant polypropylene and stainless steel.

Flame Retardant Polypropylene (PPs)

In domestic use, PPs chimneys are the most affordable and convenient in terms of installation. Generally speaking, polypropylene chimneys are also used with traditional boilers most modern designs, but still the service life in this case is limited due to the relatively high temperature of the flue gases.

In the case of condensing boilers, the exhaust temperature is low enough to have no effect on the strength of the chimneys. In addition, polypropylene is inert to the acidic composition of the condensate formed during the combustion of hydrocarbon fuels. That is, in terms of durability, this material is ideal for use with condensing boilers.

Another feature of condensing boiler chimneys is the requirement to operate under positive pressure. That is, the connections of the elements must be tight. Silicone seals are usually used to ensure tightness. Polypropylene is convenient here because, due to its elasticity, it does not require the use of additional clamps, unlike stainless steel.

The main disadvantage of this material is the vulnerability to ultraviolet radiation, that is, such chimneys cannot be laid outdoors in the open.

It is also important to note that polypropylene must be fire resistant. This fact is usually marked with an “s” in the material designation (PPs). This type of polypropylene is more resistant to high temperatures and, equally important from a safety point of view, does not support combustion. In past years, the error of using sewer pipes for installing a chimney was quite common. pressure pipes from ordinary polypropylene in order to reduce the cost of the material. This should not be done in any case for the reasons indicated above.

Stainless steel

Acid-resistant stainless steel grades are the second most popular condensing boiler chimney material in domestic applications, and the main one in the industrial and commercial segment!

The basic requirements are the same: work under excessive pressure and resistance to chemical composition condensate. In terms of temperature, stainless steel provides a huge margin of safety.

Chimney types

Three main structural types of chimneys, each of which has a specific scope:

  • single wall;
  • double-walled (sandwich);
  • coaxial.

Single wall chimney

From the name it is clear that these are just pipes and fittings from the corresponding material. It can only be used indoors or in thermally insulated channels (for example, chimneys during reconstruction). It is usually used for flue gas emissions when the air is taken from the boiler room.

Often it is also used to make a channel for supplying air to combustion from the street. These air ducts, of course, are not subject to special requirements for temperature and chemical resistance and tightness. That is, they can be made from almost any available material. However, from the point of view of uniformity and ease of installation, the same type of single-wall chimney is usually used as for flue gas emissions.

Single-wall chimneys must not be used outdoors under any circumstances. The main problem is the constant formation of condensate in the channel. From the point of view of chemical resistance, as noted above, this is not scary, but there is a great danger of freezing the liquid inside the chimney and, as a result, narrowing the flow area of ​​the pipe. The drop in natural draft due to the cooling of flue gases for this type of boilers is not critical, as powerful fans are installed in them, providing a high value of the residual pressure.

Double-walled chimney (sandwich)

The elements of this type of chimney consist of two concentric pipes of different diameters, the space between which is filled with a heat-insulating material, usually stone wool non-combustible.
There are no special requirements for acid and thermal resistance to the outer pipe, only resistance to atmospheric conditions (precipitation, ultraviolet) and mechanical strength are needed. Therefore, in the case of stainless steel double-walled chimneys, the inner and outer pipes are usually made of different steel grades to optimize cost. There are options with execution outer pipe from aluminium.

Double wall chimneys can be used both indoors and outdoors.

Due to the low temperature of flue gases and the absence of the likelihood of burns, in the case of condensing boilers, only the outer part of the chimney is usually made as a double-walled version, and for the inside, you can use a regular single-walled pipe.

coaxial chimney

Again, based on the name, it is clear what this chimney is: two concentric pipes with an empty space between them.

The main feature of this type is that it is used both for the emission of flue gases (through inner tube), and for air intake for combustion (through the space between the pipes). Accordingly, when using it, it is not necessary to constantly ensure the supply of combustion air to the boiler room. In addition, the incoming air is heated from flue gases, thereby increasing the overall efficiency of the boiler house.

Laying coaxial chimneys is also allowed only indoors, the length of the outer section in our conditions should be no more than one meter. Frequent problem in conditions cold winter is the freezing of ice at the end of the chimney. This happens due to the sharp cooling of the flue gases at the outlet upon contact with cold air entering the combustion through the gap between the pipes. To solve this problem, it is possible to cut a section of the outer pipe in the area of ​​​​the end of the chimney in order to separate the flue gas emission and air intake; or use the factory winter options for the end of the coaxial pipe.

This type of chimney is made of both plastic and stainless steel.

Basic schemes for installing chimneys for condensing boilers

All chimney schemes for condensing boilers are divided into two main types: with air intake for combustion from the room and from the street. Naturally, in the domestic normative documentation these types of smoke exhaust and the requirements for them are described, but in the documentation for the boilers there are usually names according to European standards. The chimney with air intake from the boiler room is designated as “Bxx”, from the street - as “Cxx”. The first index varies depending on the specific scheme, the second - on the location of the fan relative to the boiler heat exchanger. In all modern condensing boilers, the fan is located in front of the heat exchanger, which is indicated by the index “3”. Below are the main schemes using wall-mounted boilers as an example:

For domestic capacities, the calculation of the chimney is usually optional, it is enough to follow the recommendations of the boiler manufacturer for the maximum length, taking into account the shaped elements (elbows, tees, etc.). In the case of industrial boilers, a flue gas calculation is mandatory, you can contact the chimney manufacturer for it.

Combustion air intake from the room

The easiest way to organize the removal of flue gases. Almost always used for large capacity boilers: industrial or commercial, when floor standing boilers are used. It is also often found in domestic use.

Two main requirements when using such schemes: ensuring the necessary air flow into the boiler room and its purity. For boilers of large capacities, this is usually not a problem, since these points are carefully taken into account at the design stage. In private boiler houses, a situation often occurs when sufficient air flow is not provided; or it is carried out through adjacent rooms, where, after starting the boiler, finishing work continues, which contributes to the presence of fine dust in the air and clogging of the internal elements of the boiler. Naturally, this state of affairs should be avoided or special air filters should be used on the boilers.

In this case chimney must necessarily be brought above the roof level from the zone of the so-called “wind backwater”.

This is necessary in order to exclude the influence of air pressure fluctuations on the smoke removal process.

Air intake for combustion from the street

In this case, two main subtypes of the chimney are used: coaxial and separate.

coaxial chimney

As mentioned above, it is distributed mainly in domestic use with wall-mounted boilers. In a private house, a coaxial chimney is especially convenient in that it is enough to simply bring it horizontally beyond the wall, without constructing a vertical shaft that extends beyond the roof level. Perhaps this is due to the fact that the areas of air intake and smoke emission are located nearby in the same pressure zone, and thus are not affected by the wind.

There remains, however, the question of dispersion of flue gases in the atmosphere. Emissions from modern condensing boilers are environmentally friendly, but the chimney must comply with regulations for distances from windows, doors, ventilation grills, and adjacent land. In order to combine the convenience of installing a coaxial chimney indoors and using a double-walled pipe outdoors, you can use special adapter kits.

In case of modernization of an existing boiler house with brick chimneys there is a version with a coaxial pipe to the area of ​​\u200b\u200bthis chimney. Further, a new stainless steel pipe is laid inside it (single-walled can be used). Air intake is carried out through the gap between steel pipe and brick chimney.

The most diverse version of the organization of the chimney in terms of execution options. Nevertheless, it is rare in private construction and industrial boiler houses. Since for condensing boilers in the first case it is usually easier to use a coaxial chimney, in the second - air intake from the room.

Often found in apartment buildings with separate heat generators for each apartment, according to the following scheme:

For the selection and purchase of a chimney for a condensing boiler, please contact our .

Users of our portal have unique opportunity- follow how, within the framework of the project with FORUMHOUSE, we, together with our partners, are building a comfortable and energy-efficient Vacation home. To do this, when building a cottage, the most modern materials and technology.

UWB was chosen as the foundation, and heating systems - underfloor heating. In addition, a wall-mounted condensing gas boiler has become a boiler room. About why this particular equipment was chosen for our project, and what are the advantages of its work, in the format of a master class, the technical specialist of the company will tell you.

  • The principle of operation of a condensing gas heat generator.
  • Benefits of using a condensing gas boiler.
  • In which heating system is it best to use this equipment.
  • What to pay attention to when operating a condensing gas boiler.

The principle of operation of the condensing gas heat generator

Before we talk about the nuances of condensing technology, we note that an energy-efficient, and therefore comfortable and economical country house is a balanced building. This means that, in addition to a closed thermal insulation circuit, all elements of the cottage, including the engineering system, must be optimally matched to each other. That is why it is so important to choose a boiler that goes well with the low temperature heating system"warm floor", and will also reduce the cost of purchasing energy in the long term.

Sergey Bugaev Ariston Technician

In Russia, unlike European countries, condensation gas boilers less common. In addition to environmental friendliness and greater comfort, this type of equipment allows you to reduce heating costs, because. such boilers work 15-20% more economically than conventional ones.

If you look specifications condensing gas boilers, then you can pay attention to the efficiency of the equipment - 108-110%. This is contrary to the law of conservation of energy. While, indicating the efficiency of a conventional convection boiler, manufacturers write that it is 92-95%. Questions arise: where do these numbers come from, and why does a condensing gas boiler work more efficiently than a traditional one?

The fact is that such a result is obtained thanks to the method of heat engineering calculation used for conventional gas boilers, which does not take into account one important point evaporation/condensation. As is known, during the combustion of fuel, for example, main gas (methane CH 4), thermal energy, and also carbon dioxide (CO 2), water (H 2 O) in the form of steam and a number of other chemical elements are formed.

In a conventional boiler, the temperature of the flue gases after passing through the heat exchanger can reach up to 175-200 °C.

And water vapor in a convection (conventional) heat generator actually “flies into the pipe”, taking part of the heat (generated energy) with it into the atmosphere. Moreover, the value of this "lost" energy can reach up to 11%.

To increase the efficiency of the boiler, it is necessary to use this heat before it leaves, and transfer its energy through a special heat exchanger to the heat carrier. To do this, it is necessary to cool the flue gases to a temperature of the so-called. "dew point" (about 55 ° C), at which water vapor condenses with the release of useful heat. Those. - to use the energy of the phase transition for maximum use calorific value of the fuel.

We return to the calculation method. Fuel has a lower and higher calorific value.

  • The gross calorific value of a fuel is the amount of heat released during its combustion, taking into account the energy of water vapor contained in flue gases.
  • The net calorific value of a fuel is the amount of heat released without taking into account the energy hidden in water vapor.

The efficiency of the boiler is expressed in the amount of thermal energy obtained from the combustion of fuel and transferred to the coolant. Moreover, indicating the efficiency of the heat generator, manufacturers can calculate it by default using the method using the net calorific value of the fuel. It turns out that real efficiency of a convection heat generator is actually about 82-85% , a condensation(remember about 11% of the additional heat of combustion, which he can "pick up" from water vapor) - 93 - 97% .

This is where the efficiency figures for a condensing boiler appear, exceeding 100%. Thanks to high efficiency such a heat generator consumes less gas than a conventional boiler.

Sergey Bugaev

Maximum efficiency condensing boilers provide if the temperature of the return line of the coolant is less than 55 ° C, and these are low-temperature heating systems "warm floor", "warm walls" or systems with an increased number of radiator sections. In ordinary high temperature systems the boiler will operate in condensing mode. Only in very coldy we will have to maintain a high temperature of the heat carrier, the rest of the time, with weather-dependent regulation, the temperature of the heat carrier will be lower, and due to this, we will save 5-7% per year.

The maximum possible (theoretical) energy savings when using the heat of condensation is:

  • when burning natural gas - 11%;
  • during combustion liquefied gas(propane-butane) - 9%;
  • when burning diesel fuel (diesel fuel) - 6%.

Benefits of using a condensing gas boiler

So, we figured out the theoretical part. Now we will tell you how the design features of a condensing boiler affect its efficiency and durability. At first glance, it seems that it is possible to use the additional energy of water vapor hidden in the flue gases in a conventional boiler, specially “driving” it into a low-temperature mode of operation. For example, by connecting the boiler (this is wrong) directly to the underfloor heating system or by significantly lowering the temperature of the coolant circulating in the radiator heating system. But, we already wrote above that when the main gas is burned, a whole “bunch” of chemical elements is formed. Water vapor contains carbon dioxide and carbon monoxide, nitrogen oxides, and sulfur impurities. During condensation and the transition of steam from a gaseous to a liquid state, these impurities end up in water (condensate) and a weak acid solution is obtained at the output.

Sergey Bugaev

The heat exchanger of a conventional boiler will not withstand long-term operation in an aggressive chemical environment; over time, it will rust and fail. The heat exchanger of the condensing boiler is made of materials that are corrosion and acid resistant. The most resistant material is stainless steel.

In the manufacture of the condensing boiler, only durable and wear-resistant materials are used. This increases the service life and reliability of this equipment, and reduces maintenance costs.

In addition, increased requirements are also imposed on other structural elements of the condensing heat generator, because. it is required to cool the flue gases to the required temperature. For this purpose, the boiler is equipped with a forced draft burner with a high degree of modulation. Such a burner operates in a wide power range, which allows you to optimally regulate the heating of water. Also, condensing boilers are equipped with automation, which ensures accurate maintenance of the combustion mode, the temperature of the exhaust gases and water in the return line. Why are they set circulation pumps, smoothly changing the pressure force of the coolant flow, and not like simple 2 and 3-speed ones. With a conventional pump, the coolant flows through the boiler at a constant speed. This leads to an increase in the temperature in the "return", an increase in the temperature of the flue gases above the dew point, and, consequently, a decrease in the efficiency of the equipment. It is also possible to overheat the heating system (underfloor heating) and reduce thermal comfort.

Important nuance: the burner of a conventional boiler cannot operate at a power lower than 1/3 of the maximum (nominal) power of the heat source. The burner of the condensing boiler can operate at a power of 1/10 (10%) of the maximum (nominal) power of the heat source.

Sergey Bugaev

Consider the following situation: the heating season has begun, the temperature outside is -15 °C. The power of a conventional boiler installed in the house is 25 kW. Minimum power(1/3 of the maximum), on which it can operate - 7.5 kW. Assume that the heat loss of the building is 15 kW. Those. the boiler, continuously working, compensates for these heat losses, plus there is a power reserve. A few days later there was a thaw, which, you see, often happens during the winter. Eventually outdoor temperature now around 0°C or a little lower. The heat losses of the building, due to the increase in temperature outside, have decreased and now amount to approximately 5 kW. What will happen in this case?

An ordinary boiler cannot working in continuous mode, to give out 5 kW of power necessary to compensate for heat losses. As a result, it will go into the so-called cyclic mode of operation. Those. will constantly turn the burner on and off, or the heating system will overheat.

This mode is unfavorable for the operation of the equipment and leads to its accelerated wear.

A condensing boiler, with the same power and in a similar situation, will quietly give out 2.5 kW of power (10% of 25 kW) in continuous operation, which directly affects the service life of the heat generator and the level of comfort in a country house.

Condensing boiler, supplemented by weather-compensated automation, adapts flexibly to changes temperature regime throughout the heating season.

Modern automation makes it possible to significantly simplify the process of controlling the boiler, including remotely, using a special mobile application for smartphones, which increases the usability of the equipment.

We add that the heating season in Russia, depending on the region, averages 6-7 months, starting in the fall, when it is still not very cold outside, and lasts until spring.

Approximately 60% of this time, the average daily temperature outside is around 0 °C.

It turns out that the maximum power of the boiler may be required only in a relatively short period of time (December, January), when real frosts have set in.

In other months, the boiler is not required to reach the maximum operating mode and increased heat transfer. Consequently, a condensing boiler, unlike a conventional one, will work effectively both with temperature differences and with a slight frost. At the same time, gas consumption will decrease, which, in tandem with low temperature system heating (underfloor heating) will reduce the cost of purchasing energy.

Even when using a condensing boiler together with high-temperature radiator heating, this equipment works 5-7% more efficiently than the traditional one.

Sergey Bugaev

In addition to efficiency, an important advantage of condensing boilers is the ability to obtain high power with a compact size of equipment. A wall-mounted condensing gas boiler is especially relevant for small boiler rooms.

In addition, the condensing boiler has a turbocharged burner, which allows you to abandon the standard expensive chimney and simply lead the coaxial chimney through a hole in the wall. This simplifies the installation of equipment or the installation of a new condensing boiler to replace the old conventional one, when renovating an existing heating system.

Features of operation of a condensing gas boiler

Frequent questions from consumers: what to do with the condensate obtained during the operation of the boiler, how harmful it is, and how to dispose of it.

The amount of condensate can be calculated as follows: 0.14 kg per 1 kWh. Therefore, a condensing gas boiler with a power of 24 kW when operating at 12 kW of power (because most of the heating period the boiler works with modulation, and the average load on it, depending on the conditions, can be below 25%) on a fairly cold day produces 40 liters of condensate in low temperature mode.

Condensate can be drained into the central sewer, provided that it is diluted in a ratio of 10 or better 25 to 1. If the house is equipped with a septic tank or a local treatment plant, condensate neutralization is required.

Sergey Bugaev

The neutralizer is a container filled with marble chips. Filler weight - from 5 to 40 kg. It must be changed manually on average once every 1-2 months. Condensate, usually passing through the neutralizer, by gravity enters the sewer.

Summarizing

This is a modern equipment, characterized by reliability, economy and efficiency. Emissions of harmful substances into the atmosphere are also reduced, which is especially important when environmental standards are tightened. In addition, the installation of this type of heat generator, by reducing gas consumption, will reduce heating costs in the long term and increase the level of comfort in a country house.