Condensate in the chimney of an automatic gas boiler. Why is the boiler crying

Why does condensation form in the boiler and in the chimneys? This phenomenon is often accompanied by a sharp disgusting smell. Where does it come from?

In general, any hydrocarbon fuel, which includes gas, coal, firewood, as well as oil and all its derivatives - all these fuels contain hydrogen, which is clear even from the name: hydrocarbons. When they are burned, water is also synthesized, which is in a vapor state in the composition of flue gases.

In addition to the synthesized water, there is also moisture from the air that is fed into the furnace. In addition, there is moisture in the composition of the fuel itself. For example, wood contains the largest amount, and coal contains the least amount of water.

All this water is in flue gases in a vaporous state with a high temperature. At the exit from the furnace of a wood-burning boiler, the flue gas temperature can range from 600 to 800 degrees.

Passing further, through the registers of the boiler heat exchanger and smoke channels, these gases give off heat and cool. When their temperature reaches the condensation temperature (dew point), then this phenomenon occurs. That is, water from the vapor state is deposited on the colder surfaces of the registers and the walls of the chimneys.

The dew point is far from a constant value. The condensation temperature depends on many factors, which are parameters such as absolute and relative humidity of gases, their temperature and even the content of excess air in them.

In practice, for wood-burning solid fuel boilers, the dew point temperature is considered to be approximately 40 degrees. That is, on any surfaces below this temperature, condensate will fall along the flue gases.

At the very beginning of the boiler furnace, condensate forms on almost all surfaces until they have warmed up to a temperature above the dew point. And this point over time moves further and further away from the furnace towards the pipe head.

When, finally, this entire system is warmed up, moisture will no longer condense on the surfaces of the system, but in the air outside the system in the form of white smoke from the chimney. And the moisture that has condensed on the walls will now evaporate and move along with the flue gases to the exit.

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Dealing with condensation is easy. Of course, it is impossible to defeat the laws of physics and prevent it altogether, but it is possible to ensure that there are no cold surfaces in the way of gases or they are cold for a minimum time from the start of the furnace.

The first measure is the mandatory insulation of the pipe, whatever it may be, brick, steel or whatever. The second measure related directly to the boilers is to prevent the supply of water with a temperature below the dew point (40 degrees) to the heat exchange registers. We read about this topic in the article

In the process of burning fuel in a stove or fireplace, flue gases are formed that are saturated with water vapor and soot. Passing through the chimney, these gases are cooled, and the steam begins to condense on its walls, soot settles there. As a result, if there is too much condensate, a black, tarry liquid with an unpleasant odor is formed, which seeps through the masonry, dampness is created, the furnace structure becomes wet and gradually collapses.

Each type of pipe has its own characteristics, due to which condensation forms in the chimney, but there are still a number of main reasons:

• Atmospheric precipitation enters the smoke channel.
• Low flue gas outlet temperature.
• A sharp change in temperature.
• Pipes are not warm enough.
• High moisture content of the fuel.
• Bad chimney draft.
• Clogging or technically incorrect design of the chimney.
• Large temperature difference due to wall thickness.
• Excess chimneys in one outlet pipe.

How to get rid of condensation in a brick chimney

brick chimneys- a very common option for ovens. When observed, they are relatively inexpensive, reliable and durable. If brick masonry darkens, becomes damp, stains appear on it- this is a clear sign of the condensation process. There are several options for solving the problem.

During the operation of the heating system, the appearance of moisture in the chimney harms not only the chimney itself, but also the heater. Reacting with combustion products, moisture turns into chemically aggressive substances that disrupt the operation of the heating system.

It is impossible to get rid of condensate completely, but you can minimize its amount and prevent undesirable consequences.

Any fuel for a boiler, stove or fireplace, when burned, releases water vapor, which cools down in the chimney pipe and forms a deposit in the form of drops on the walls. This happens due to the temperature difference at the outlet of the heating unit and in certain parts of the chimney.

Additionally, moisture can enter the smoke channel from the outside during rain. The chemical reaction of water with soot and resins leads to the formation of acids and alkalis.

On smooth walls, condensate flows down, where it accumulates, preventing smoke from being removed and worsening traction. Rough surfaces trap and absorb moisture, subject to corrosion and premature failure.

In addition, substances accumulated in the chimney can enter the room, causing an unpleasant odor and causing harm to health.

Note! Condensation can form not only from the inside, but also from the outside of the chimney - at very different temperatures in the pipe and on the street. The result may be the destruction of the pipe itself, if it is made of moisture-absorbing materials, as well as walls and roofs in contact with the chimney.

Factors affecting the formation of condensate

The process of formation of condensate in the chimney channel depends on several factors:

• Humidity of the fuel used by the heating system. Even seemingly dry firewood contains moisture, which turns into steam when burned. Peat, coal and other combustible materials have a certain percentage of moisture content. Natural gas, burning in a gas boiler, also releases a large amount of water vapor. There is no absolutely dry fuel, but poorly dried or damp material increases the condensation process.
• Traction level. The better the draft, the faster steam is removed and less moisture settles on the pipe walls. It simply does not have time to mix with other combustion products. If the draft is bad, a vicious circle is obtained: condensate accumulates in the chimney, contributing to clogging and further worsening the circulation of gases.
• The temperature of the air in the pipe and the gases leaving the heater. The first time after kindling, smoke moves along an unheated channel, also having a low temperature. It is at the start that the greatest condensation occurs. Therefore, systems that operate constantly, without regular shutdowns, are least susceptible to condensation.
• Temperature and humidity of the environment. In the cold season, due to the temperature difference inside the chimney and outside, as well as increased air humidity, condensate forms more actively on the outer and end parts of the pipe.
• The material from which the chimney is made. Brick and asbestos cement prevent the dripping of moisture drops and absorb the resulting acids. Metal pipes can be prone to corrosion and rust. Chimneys made of ceramic blocks or stainless steel sections prevent chemically aggressive compounds from catching on a smooth surface. The smoother, smoother the inner surface and the lower the moisture absorption capacity of the pipe material, the less condensate is formed in it.
• Integrity of the chimney structure. In case of violation of the tightness of the pipe, the appearance of damage on its inner surface, the draft deteriorates, the channel becomes clogged faster, moisture from the outside can get inside. All this leads to increased steam condensation and deterioration of the chimney.

The surrounding air always contains moisture. Think foggy windows in damp weather or wet walls in the bathroom. When air or flue gases cool down to a critical temperature (to the "dew point") in contact with the colder walls of the boiler or chimney, condensate drops form. Many boiler owners immediately begin to panic as soon as they see water in the boiler and believe that the boiler has leaked. Mixing with soot particles, this water becomes black, thick, "like oil." This substance covers the heat transfer surfaces of the boiler and significantly reduces heat transfer, resulting in power loss. In addition, this liquid has a very aggressive property - it begins to corrode the boiler walls and welds due to the formation of sulfurous acid. If nothing is done, the heat exchanger and chimney will be damaged.

Condensation can form in the boiler itself (on the walls of the furnace and in the heat exchanger), as well as in the chimney. At the same time, owners of pellet boilers and long-burning solid fuel boilers often face this, since the flue gases there have a lower outlet temperature. But all problems can be solved even when designing a boiler room and using high-quality fuel.

The amount of condensate depends on the ambient air temperature, air humidity and the moisture content of the fuel used.

Chimney problems

Often, when using a solid fuel boiler, they do not pay much attention to the chimney. But the operation of the entire heating system depends on it almost 100%. There is no sufficient draft - the power of the boiler is lost, the boiler starts to smoke. A chimney of a smaller diameter is used - it also leads to a significant decrease in power, since there will not be enough oxygen to burn the required amount of fuel per unit time. A cold pipe, no insulation - condensate forms, which begins to flow down the pipe walls into the boiler.

If the pipe is insulated, but a thick-walled steel pipe is used, then condensation will form until the entire pipe warms up. If it is a pellet boiler, then it will be quite difficult to warm up such a pipe, since the exhaust gases have a low temperature. In addition, the pellet boiler in the room temperature maintenance mode can be off for a long time, and when it is turned on, condensation will again occur. Therefore, for any pellet boilers, we recommend using only insulated sandwich pipes (they usually have a wall thickness of up to 1 mm). In extreme cases, you can connect the boiler to a brick chimney. Long-burning boilers can also be in combustion maintenance modes with low flue gas temperatures, so it is also desirable to use sandwich pipes and brick chimneys for them. If the boiler will be mainly operated in maximum power modes, then it is allowed to use thick-walled insulated pipes.

In order to reduce the cost of purchasing a chimney, it is enough to insulate a part of the chimney located in unheated premises and on the street. In addition, in this case, part of the heat from the uninsulated pipe will be transferred into the room, further reducing heating costs.

A cold brick pipe can also be destroyed by such acid. Over time, traces of such an impact are noticeable on the pipe, and through the seams in the brickwork, smoke begins to enter the premises of a private house. High-quality solid bricks should be used and masonry joints should be filled with high quality. It is recommended that the pipe wall thickness be at least 25cm. To connect the brick pipe to the boiler, you can use a steel bend of a suitable size.

The easiest and most costly way to solve problems with a chimney is to use a ready-made insulated stainless steel pipe - a sandwich pipe. Such a pipe consists of two concentric pipes, between which there is a heater. The thickness of the insulation layer and the material of the inner pipe is selected based on the characteristics of the heating boiler. Boiler characteristics include flue gas temperature and fuel used. For solid fuel boilers, pipes made of high-quality stainless steels that are resistant to aggressive environments are used, for example, AISI 304, 310 or 316 steel. Sandwich pipes are quite light, and their installation is not difficult. Pipes are inserted one into another using crimping clamps. There are various connecting elements of such smoke systems - tees, transitions from the boiler nozzle to the main pipe, bends, passages through walls, passages through ceilings and roofs.

An asbestos-cement chimney can be used. However, such pipes are "afraid" of flue gases that are too hot. Therefore, it is recommended to make a section of about 2 meters at the outlet of the boiler from a steel pipe, and then use asbestos-cement.

Proper operation of the boiler and heating system

Do not turn on the circulation pump of the heating system at a negative temperature in the heating system. It is advisable to turn on the pump after the boiler has warmed up to a temperature of at least 50-60 degrees.
Otherwise, there is also a problem of condensate formation in the boiler furnace and heat exchanger.
As the boiler operates and the heating system warms up, the condensate will, of course, evaporate, but this takes time and additional energy to evaporate moisture.

The question arises - how to control the inclusion of the pump?

The first option - free of charge - we stand next to the boiler and control the temperature with a thermometer at the boiler outlet. After the boiler has warmed up, it is necessary to turn on the pump at the minimum speed and observe the temperature change. If the temperature rises quickly enough, then it is necessary to increase the speed of the circulation pump. The optimal mode from the point of view of efficiency and durability of the boiler is the flow of coolant into the boiler with a temperature of 50-60 degrees.

The second option is to use an automation unit that controls the operation of the heating system pump. The control unit monitors the temperature at the outlet of the boiler and turns on the pump only when the temperature at the outlet of the boiler is above the set threshold value. In long-burning START boilers, as well as in pellet boilers, circulation pumps are connected to the automation unit, in which these pump switching algorithms are organized.

The third option is to organize a small circulation circuit through the boiler using a three-way valve and an additional circulation pump. This ensures the most correct mode of operation of the heating boiler. The boiler operates in the same mode and the possibility of condensate formation is almost completely excluded (only during the start-up period).

Choice of quality fuel

You can also extend the life of your boiler and make it easier for yourself to clean it if you use high-quality fuel - fuel with low humidity. Naturally, the most ideal fuel with a moisture content of less than 10% is pellets and other briquetted fuels. Briquetted fuel will also allow you to get a longer burning of one fuel tab. Pellets can only be used in a specialized pellet boiler. Thus, a pellet boiler and pellet fuel are an ideal pair that makes life as easy as possible for the owner of such an automatic solid fuel boiler.

Condensation on the pipe of a gas boiler is formed due to the difference in ambient temperatures and the walls of the flue channel. In winter, the condensate freezes, and icicles form on the head of the pipe, and ice plugs form in the chimney. Over time, the ice thaws, moisture flows down the pipe, the chimney and adjacent structures get wet and gradually collapse.

Condensation in the gas boiler pipe also leads to negative consequences. Water vapor, which is contained in the combustion products of the fuel, condenses on the cold walls of the chimney. As a result, moisture is formed, which combines with the salts of flue gases. In this case, aggressive acids are formed that destroy the chimney and other surfaces.

Video answer: why the chimney gets wet

How to avoid negative consequences

The smoke channel is intended for removal of products of combustion of fuel from a copper or other heating device by means of natural draft. This is an important link in the gas supply system at home. Not only the life and health of residents, but also the trouble-free operation of gas equipment depends on the correct arrangement of the chimney. As a result, strict requirements are imposed on the chimneys of gas boilers, compliance with which guarantees the efficient and safe operation of the equipment. There are several main criteria that a smoke exhaust system must meet:

• thermal insulation;
• anti-corrosion;
• water resistance;
• tightness.

A condensate trap with a tube to drain condensate is also required. When installing a “correct” chimney, the installation of fungi, umbrellas and other elements is prohibited. In this case, there is a risk of carbon monoxide entering the living space.

Signs of condensation in the chimney pipe

Types of chimneys

Modern boilers have a high efficiency and are extremely economical. As a result, the temperature of the exhaust gases is low, it is not enough to warm the flue. The equipment is periodically turned off, which entails the formation of condensate in the gas outlet pipe. It is important to consider the features of the boiler when choosing a material for the chimney. Condensate flows down through a smooth and water-resistant pipe without destroying it. If the smoke channel has a porous and uneven structure, condensate is absorbed into it, which leads to destructive consequences. There are several options for chimneys.

Brick chimney is rapidly deteriorating

Classic brick

Brick flue accumulates heat and maintains draft. At the same time, it has a lot of negative properties. The complexity of construction, high cost, intensive destruction due to the absorption of condensate - this is not a complete list of the disadvantages of a brick chimney. These problems can be solved by "sleeving" - mounting a stainless steel channel into the chimney.

stainless steel

The chimney is made according to the principle of a sandwich system - a pipe of a smaller diameter is located in a pipe of a larger diameter, between them a mineral wool insulation. The heat-insulating layer may have a different thickness depending on the purpose and location of the chimney.

There are a lot of adapters and connecting parts on sale, which allows you to assemble a chimney of any complexity. At the same time, it meets all the necessary requirements, has a perfectly smooth inner surface, and does not accumulate soot and condensate. Another undoubted advantage is the high resistance to aggressive acids.

Stainless steel system - best value for money

coaxial chimney

The system is built on the principle of "pipe in pipe". At the same time, they are interconnected with jumpers and do not touch. Coaxial chimney is fundamentally different from other designs. The main difference is that it performs two functions: the removal of fuel combustion products to the outside and the intake of fresh air to maintain the combustion process in the chamber. So condensate on the air intake pipe of the gas boiler does not form in principle.

Coaxial chimney has many advantages

The advantage is the small length of the structure - no more than 2 meters, as well as the fact that the laying is carried out through the wall of the room. The design helps to increase the efficiency of the entire heating system, which ensures complete combustion of gas. At the same time, air is taken from outside the room, which makes the operation of the system comfortable and safe.

Video advice on how to improve the design:

Ceramic

Ceramic products are strong and durable. The ceramic chimney has the same qualities. It is a robust and acid-resistant construction. Among other things, the system is easy to maintain and has fire-fighting properties. Ceramics heats up quickly and cools down for a long time. It should be noted that the system is expensive and the process of its installation requires the participation of specialists.

Ceramic chimney reliable and durable

General rules for the operation of chimneys

When installing a chimney, it is important to ensure:

• removal of condensate using a condensate collection tank;
• maximum tightness of the system;
• system isolation;
• good traction;
• vertical shape of the chimney;

Important! The head of the pipe must rise above the roof surface by at least 0.5 m so that it does not fall into the zone of wind backwater.

The layout of the chimney on the roof

Installation and maintenance of the chimney is a vital process that does not tolerate negligence. From time to time, professional regular cleaning and revision of the chimney is necessary. After all, the visit of a specialist will help not only solve pressing problems, but also identify shortcomings in the future.