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All about boiler efficiency

What is boiler efficiency

The efficiency of a heating boiler is the ratio of useful heat consumed to produce steam (or hot water), to the available heat of the heating boiler. Not all the useful heat generated by the boiler unit is sent to consumers; part of the heat is spent on its own needs. Taking this into account, the efficiency of a heating boiler is distinguished by the heat generated (gross efficiency) and by the heat released (net efficiency).

The difference between the generated and released heat is used to determine the consumption for auxiliary needs. Not only heat is consumed for its own needs, but also electrical energy (for example, to drive a smoke exhauster, fan, feed pumps, fuel supply mechanisms), i.e. consumption for own needs includes the consumption of all types of energy spent on the production of steam or hot water.

* To buy a Unique boiler, go to the appropriate section. And if you need heating boilers wholesale, then go here.

How to calculate boiler efficiency

As a result, the gross efficiency of a heating boiler characterizes the degree of its technical perfection, and the net efficiency characterizes its commercial profitability. For a boiler unit, gross efficiency, %:
according to the direct balance equation:

ηbr = 100 Qpol / Qpp

where Qfloor is the amount of useful heat, MJ/kg; Qрр - available heat, MJ/kg;

according to the reverse balance equation:

ηbr = 100 – (q2 + q3 + q4 + q5 + q6),

where q is heat loss in%:

q2 - with exhaust gases;
q3 - due to chemical underburning of flammable gases (CO, H2, CH4);
q4 - with mechanical underburning;
q5 - from external cooling;
q6 - with physical heat of slag.

Then the net efficiency of the heating boiler according to the reverse balance equation

ηnet = ηbr - qs.n

where qс.н is energy consumption for own needs, %.

Determination of efficiency according to the direct balance equation, they are carried out mainly when reporting for a separate period (decade, month), and according to the reverse balance equation - when testing a heating boiler. Calculating the efficiency of a heating boiler using reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption.

How to increase the efficiency of a gas boiler with your own hands

Create the right conditions operation gas boiler and thus you can actually increase the efficiency without calling a specialist, that is, with your own hands. What do I need to do?

Adjust the blower damper. This can be done experimentally by finding at what position the coolant temperature will be highest. Carry out control using a thermometer installed in the boiler body.
Be sure to ensure that the heating system pipes do not become overgrown from the inside, so that scale and dirt deposits do not form on them. Today it has become easier with plastic pipes, their quality is known. Still, experts recommend periodically purging the heating system.
Monitor the quality of the chimney. Do not allow it to become clogged or soot to stick to the walls. All this leads to a narrowing of the cross-section of the outlet pipe and a decrease in the boiler draft.
A prerequisite is cleaning the combustion chamber. Of course, gas does not smoke much like wood or coal, but it is worth washing the firebox at least once every three years to clear it of soot.
Experts recommend reducing chimney draft during the coldest time of the year. For this you can use special device– draft limiter. It is installed at the very top edge of the chimney and regulates the cross-section of the pipe itself.
Reduce chemical heat losses. There are two options here to achieve the optimal value: install a draft limiter (this has already been mentioned above) and immediately after installing the gas boiler, carry out proper adjustment of the equipment. We recommend entrusting this to a specialist.
You can install a turbulator. These are special plates that are installed between the firebox and the heat exchanger. They increase the area of thermal energy extraction.

The efficiency of a boiler unit or the efficiency of a boiler unit is the ratio of the amount of heat used in the boiler unit to the amount of heat expended in the fuel. Part of the steam produced in the boiler unit is directly spent on its own needs, for example, on feed pumps, blower fans, smoke exhausters, and blowing heating surfaces. Taking these costs into account, the concept is introduced Boiler unit net efficiency.

Heat used in the boiler unit to produce steam or hot water,

Where IN - hourly fuel consumption, kg/h (m3/h);

D- hourly productivity of the boiler unit, kg/hour;

q k.a - the amount of heat transferred to water in the boiler unit to convert it into steam or to produce hot water and referred to 1 kg of steam or water, kJ/kg (kcal/kg);

ŋ k.a - efficiency of the boiler unit.

For a boiler unit that produces saturated steam

Where i" - enthalpy of saturated steam;

i p.v - enthalpy of feed water;

q pr- amount of heat removed from the boiler unit with blowdown water, kJ/kg (kcal/kg); usually q pr= (0.01-0.02) · i", Where i" - heat content of water at temperature t n.

For a hot water boiler unit that produces hot water

Where i 1 - enthalpy of water entering the boiler; i 2 is the enthalpy of water leaving the boiler.

If the amount of steam produced and its enthalpy are known, as well as the hourly fuel consumption and the heat of combustion of the fuel, then the efficiency of the boiler unit can be determined, %:

For modern boiler units the value q 1, depending on the steam output of the boiler unit, the temperature of the flue gases, the type of fuel burned and the method of its combustion, can vary within a very wide range from 75 to 80% for boiler units of small capacity, in which solid fuel is burned in layered furnaces, and up to 91-95 % for large boiler units with flaring fuel combustion. The highest efficiencies are obtained for boiler units operating on liquid and gaseous fuels.

For boiler units of small capacity, heat loss ranges from 20 to 25%, and for large ones from 5 to 9%. The main heat losses are losses with flue gases q 2

Example.

Determine the efficiency of the boiler unit and estimate the heat losses of the boiler unit with a steam capacity of Q = 10 tons/hour with steam parameters: pressure P= 1.4 MPa (14 kgf/cm2) and temperature t = 197.3°C. Hourly fuel consumption 1500 kg, feed water temperature 100°C, fuel combustion heat Q p n = 20647 kJ/kg (4916 kcal/kg). The heat losses of the boiler unit are assessed using the average values given in the relevant sections. Sizeq PR ( amount of heat removed from the boiler unit with blowdown water) take equal to 0.

According to the table and specified steam parameters: pressure R and temperature t we find its enthalpy ~ 2790 kJ/kg (666 kcal/kg). At 100°C the heat content of the feed water will be approximately 419 kJ/kg (100 kcal/kg). Therefore, the heat received by 1 kg of steam according to the formula isq To

. A = 2790 - 419 = 2371 kJ/kg ( q

To . a = 666 - 100 = 566 kcal/kg).

The amount of heat loss

Σ q i = 100 - ŋ k.a = 100 - 76.8 = 23.2%. Based on averages q 2 ,q 3 , q 4 given in § Heat balance of the boiler unit, we find q 2 = 12,5%, q 3 = 1%, q 4 = 6.25%. Consequently, the amount of losses to the environment q 5 = Σ q i- q 2 - q 3 - q 4 = 23,2 - 12,5 - 1 - 6,25 = 3,45%. ,

General equation heat balance boiler unit

The ratio connecting the heat input and consumption in a heat generator constitutes its heat balance. The goals of compiling a heat balance of a boiler unit are to determine all incoming and outgoing balance sheet items; calculation of the efficiency of the boiler unit, analysis of balance sheet expenditure items in order to establish the reasons for the deterioration of the boiler unit.

In a boiler unit, when fuel is burned, the chemical energy of the fuel is converted into thermal energy combustion products. The released heat from the fuel is used to generate useful heat contained in steam or hot water and to cover heat losses.

In accordance with the law of conservation of energy, there must be equality between the incoming and outgoing heat in the boiler unit, i.e.

For boiler installations, the heat balance is per 1 kg of solid or liquid fuel or 1m 3 of gas under normal conditions ( ). The items of income and consumption in the heat balance equation have dimensions MJ/m 3 for gaseous and MJ/kg for solid and liquid fuels.

The heat from fuel combustion entering the boiler unit is also called available heat, it is denoted by .In the general case entrance part The heat balance is written as:

where is the lowest calorific value of solid or liquid fuel per working mass, MJ/kg;

Lower calorific value of gaseous fuel per dry weight, MJ/m 3 ;

Physical heat of fuel;

Physical heat of air;

Heat introduced into the furnace of a boiler with steam.

Let us consider the components of the incoming part of the heat balance. In the calculations, the lowest working heat of combustion is accepted if the temperature of the combustion products leaving the boiler is higher than the condensation temperature of water vapor (usually tg = 110...120 0 C). When cooling combustion products to a temperature at which condensation of water vapor is possible on the heating surface, calculations should be performed taking into account the higher calorific value of fuel combustion

The physical heat of the fuel is equal to:

Where With T - specific heat fuel, for fuel oil and for gas;

t t – fuel temperature, 0 C.

Upon entering the boiler solid fuel has usually a low temperature approaching zero, so Q f.t. is small in importance and can be neglected.

To reduce viscosity and improve atomization, fuel oil (liquid fuel) enters the furnace heated to a temperature of 80...120 0 C, so its physical heat is taken into account when performing calculations. In this case, the heat capacity of fuel oil can be determined by the formula:

Accounting Q f.t. is carried out only when burning gaseous fuel with a low calorific value (for example, blast furnace gas) provided it is heated (up to 200...300 0 C). When burning gaseous fuels with a high calorific value (for example, natural gas), there is an increased ratio of air to gas mass (approximately 10 1). In this case, the fuel - gas is usually not heated.

Physical heat of air Q f.v. is taken into account only when it is heated outside the boiler due to an external source (for example, in a steam heater or in an autonomous heater when additional fuel is burned in it). In this case, the heat introduced by the air is equal to:

where is the ratio of the amount of air at the entrance to the boiler (air heater) to the theoretically necessary one;

The enthalpy of the theoretically required air heated before the air heater, :

here the temperature of the heated air in front of the air heater of the boiler unit is 0 C;

Enthalpy of theoretically necessary cold air, :

The heat introduced into the boiler furnace with steam during steam atomization of fuel oil is taken into account in the form of the formula:

Where G p – steam consumption, kg per 1 kg of fuel (for steam spraying of fuel oil G n = 0.3…0.35 kg/kg);

h n – steam enthalpy, MJ/kg;

2.51 is the approximate value of the enthalpy of water vapor in the combustion products leaving the boiler unit, MJ/kg.

In the absence of heating of fuel and air from external sources, the available heat will be equal to:

The consumption part of the heat balance includes usefully used heat Q floor in the boiler unit, i.e. heat expended to produce steam (or hot water), and various heat losses, i.e.

Where Q u.g. – heat loss with exhaust gases;

Q h.n. , Q m.s. – heat loss from chemical and mechanical incomplete combustion of fuel;

Q But. – heat loss from external cooling of the external enclosures of the boiler;

Q f.sh. – loss of slag with physical heat;

Q acc. – consumption (sign “+”) and supply (sign “-”) of heat associated with the unsteady thermal operating conditions of the boiler. At steady thermal state Q acc. = 0.

So the general equation for the heat balance of a boiler unit at steady state thermal mode can be written as:

If both sides of the presented equation are divided by and multiplied by 100%, we get:

Where components of the expenditure part of the heat balance, %.

3.1 Heat loss from flue gases

Heat loss with flue gases occurs due to the fact that the physical heat (enthalpy) of gases leaving the boiler at a temperature t u.g. , exceeds the physical heat of the air entering the boiler α u.g. and fuel With T t t. The difference between the enthalpy of exhaust gases and the heat entering the boiler with air from environment α u.g. , represents the heat loss with exhaust gases, MJ/kg or (MJ/m 3):

Heat loss with flue gases usually occupies the main place among the heat losses of the boiler, amounting to 5...12% of the available heat of the fuel. These heat losses depend on the temperature, volume and composition of combustion products, which, in turn, depend on the ballast components of the fuel:

The ratio characterizing the quality of the fuel shows the relative yield of gaseous combustion products (at α = 1) per unit heat of combustion of the fuel and depends on the content of ballast components (moisture) in it W r and ash A r for solid and liquid fuels, nitrogen N 2, carbon dioxide CO 2 and oxygen ABOUT 2 for gaseous fuel). With an increase in the content of ballast components in the fuel, and, consequently, the loss of heat with exhaust gases increases accordingly.

One of the possible ways to reduce heat loss with flue gases is to reduce the coefficient of excess air in the flue gases α ug, which depends on the coefficient of air flow in the furnace and the ballast air sucked into the boiler flues, which are usually under vacuum:

Possibility of reduction α , depends on the type of fuel, the method of its combustion, the type of burners and the grinding device. At favorable conditions By mixing fuel and air, the excess air required for combustion can be reduced. When burning gaseous fuel, the excess air coefficient is taken to be 1.1, when burning fuel oil = 1.1...1.15.

Air suction through the gas path of the boiler can, in the limit, be reduced to zero. However, complete sealing of the places where pipes pass through the lining, sealing of hatches and peepholes is difficult and practically = 0.15..0.3.

Ballast air in combustion products in addition to increasing heat loss Q u.g. also leads to additional costs electricity for the smoke exhauster.

Another important factor influencing the value Q ug, is the temperature of the flue gases t u.g. . Its reduction is achieved by installing heat-using elements (economizer, air heater) in the tail part of the boiler. The lower the temperature of the flue gases and, accordingly, the smaller the temperature difference between the gases and the heated working fluid (for example, air), the big square heating surface is required to cool combustion products.

An increase in the temperature of the flue gases leads to an increase in losses from Q u.g. and, consequently, to additional fuel costs to produce the same amount of steam or hot water. Due to this optimal temperature t u.g. is determined on the basis of technical and economic calculations when comparing the finished capital costs for the construction of a heating surface and fuel costs (Fig. 3.).

In addition, when the boiler is operating, the heating surfaces may become contaminated with soot and fuel ash. This leads to a deterioration in the heat exchange of combustion products with the heating surface. At the same time, in order to maintain a given steam output, it is necessary to increase fuel consumption. The drift of heating surfaces also leads to an increase in the resistance of the gas path of the boiler. In this regard, to ensure normal operation of the unit, systematic cleaning of its heating surfaces is required.

3.2 Heat loss from chemical incomplete combustion

Heat loss from chemical incomplete combustion (chemical underburning) occurs when fuel is incompletely burned within the combustion chamber and flammable gaseous components appear in the combustion products - CO, H2, CH4, CmHn, etc. the afterburning of these combustible gases outside fireboxes are almost impossible due to their relatively low temperature.

The causes of chemical incomplete combustion may be:

general lack of air;

· poor mixture formation, especially in the initial stages of fuel combustion;

· low temperature in the combustion chamber, especially in the area of fuel afterburning;

· insufficient residence time of fuel within the combustion chamber, during which chemical reaction combustion cannot be completed completely.

If there is a sufficient amount of air for complete combustion of the fuel and good mixture formation, the losses depend on the volumetric density of heat release in the furnace, MW/m3:

Where IN– fuel consumption, kg/s;

V t – volume of the firebox, m3.

Rice. 14.9 Dependence of heat loss on chemical incompleteness of combustion q x.n, %, from the volumetric density of heat release in the furnace q v, MW/m 3 .

The nature of the dependence is presented in Fig. 4. . In the area of low values (left side of the curve), i.e. at low fuel consumption B, losses increase due to a decrease in the temperature level in the combustion chamber. An increase in the volumetric density of heat release (with an increase in fuel consumption) leads to an increase in the temperature level in the furnace and a decrease

However, upon reaching a certain level with a further increase in fuel consumption (the right side of the curve), losses begin to increase again, which is associated with a decrease in the residence time of gases in the furnace volume and, therefore, the impossibility of completing the combustion reaction.

The optimal value at which losses are minimal depends on the type of fuel, the method of its combustion and the design of the furnace. For modern combustion devices, heat loss from chemical incomplete combustion is 0...2% at .when burning solid and liquid fuels:

when burning gaseous fuel:

When developing measures to reduce the value, it should be borne in mind that if conditions exist for the appearance of products incomplete combustion First of all, CO is formed as the most difficult to burn component, and then H 2 and other gases. It follows from this that if there is no CO in the combustion products, then there is no H 2 in them.

Boiler unit efficiency

Efficiency factor boiler unit is the ratio of useful heat consumed to produce steam (or hot water) to the available heat of the boiler unit. However, not all the useful heat generated by the boiler unit is sent to consumers; part of the heat is spent on its own needs. Taking this into account, the efficiency of a boiler unit is distinguished by the heat generated (efficiency - gross) and by the heat released (efficiency - net).

So, gross efficiency of a boiler unit characterizes the degree of its technical perfection, and net efficiency characterizes commercial profitability.

Efficiency - gross boiler unit can be determined either by the direct balance equation or by the reverse balance equation.

According to the direct balance equation:

For example, in the production of water vapor, the useful heat used is ( see question 2) :

Then

From the presented expression, you can obtain a formula for determining the required fuel consumption, kg/s (m 3 /s):

According to the reverse balance equation:

The determination of gross efficiency using the direct balance equation is carried out mainly when reporting for a separate period (ten-day, month), and according to the reverse balance equation - when testing boiler units. Calculating efficiency using reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption.

Net efficiency is determined by the expression:

where is the energy consumption for own needs, %.

Thus, to improve the efficiency of boiler units, it is not enough to strive to reduce heat losses; It is also necessary to completely reduce the consumption of thermal and electrical energy for own needs, which amount on average to 3...5% of the heat available in the boiler unit. The efficiency of the boiler unit depends on its load. To build the dependence, you need to subtract sequentially from 100% all losses of the boiler unit, which depend on the load, i.e.

The coefficient of performance (efficiency) of a boiler unit is defined as the ratio of the useful heat used to produce steam (or hot water) to the available heat (heat entered into the boiler unit). In practice, not all useful heat selected by the boiler unit is sent to consumers. Part of the heat is spent for its own needs. Depending on this, the efficiency of the unit is distinguished by the heat supplied to the consumer ( Net efficiency).

The difference between the generated and released heat represents the consumption for the boiler house’s own needs. Not only heat is consumed for own needs, but also electrical energy (for example, to drive a smoke exhauster, fan, feed pumps, fuel supply and dust preparation mechanisms, etc.), therefore, consumption for own needs includes the consumption of all types of energy spent on production of steam or hot water.

The gross efficiency of a boiler unit characterizes the degree of its technical perfection, and the net efficiency characterizes its commercial efficiency.

Gross efficiency of the boiler unit ŋ br, %, can be determined using the direct balance equation

ŋ br = 100(Q floor /Q r r)

or according to the reverse balance equation

ŋ br = 100-(q u.g +q h.n +q m.n +q n.o +q f.sh),

Where Q floor useful heat expended to generate steam (or hot water); Q r r- heat available from the boiler unit; q u.g +q h.n +q m.n +q n.o +q f.sh- relative heat losses by heat consumption items.

Net efficiency according to the reverse balance equation is determined as the difference

ŋ net = ŋ br -q s.n,

Where q s.n.- relative energy consumption for own needs, %.

The efficiency according to the direct balance equation is used mainly when preparing reports for a separate period (decade, month), and the efficiency according to the reverse balance equation is used when testing boiler units. Determining efficiency by reverse balance is much more accurate, since the errors in measuring heat losses are smaller than in determining fuel consumption, especially when burning solid fuels.

Thus, to improve the efficiency of boiler units, it is not enough to strive to reduce heat losses; It is also necessary to reduce in every possible way the consumption of thermal and electrical energy for our own needs. Therefore, a comparison of the operating efficiency of various boiler units should ultimately be carried out based on their net efficiency.

In general, the efficiency of a boiler unit varies depending on its load. To construct this relationship, you need to subtract sequentially all losses of the boiler unit from 100%. Sq sweat = q u.g +q x.n +q m.n +q n.o, which depend on the load.

As can be seen from Figure 1.14, the efficiency of the boiler unit at a certain load has a maximum value, i.e., operation of the boiler at this load is the most economical.

Figure 1.14 - Dependence of boiler efficiency on its load: q u.g, q x.n, q m.n., q n.o.,S q sweat- heat losses with exhaust gases, from chemical incomplete combustion, from mechanical incomplete combustion, from external cooling and total losses

Reading time: 4 min

A properly selected heating system will not only bring warmth and comfort to every home, but will also eliminate unpleasant consequences and extra costs for repairs. hot water boiler - basis heating system Houses.

Before choosing and purchasing, it is worth making a correct calculation of the efficiency of the boiler and clarifying all its parameters and factors that will affect its operation and the amount of heat generated.

What is boiler efficiency

The efficiency of steam and hot water boilers is determined by the efficiency factor - their thermal efficiency. That is, this is the volume of heat generated to produce a nominal volume of hot water in relation to the nominal volume of burned fuel.

Manufacturers indicate the initial capabilities of the equipment, where the efficiency of a hot water boiler can reach 110%, but more often their value adheres to the parameters of 95-98%. During further operation, the consumer can use technical upgrades and thermal insulation increase these indicators.

Independent calculation of the boiler efficiency is carried out at the installation site and depends on many factors, including a well-built smoke removal system, eliminating defects during installation, etc. All resources expended for the operation of the coolant (fuel, electricity) are compared with the volume of heat generated by it.

How to calculate efficiency

The gross efficiency of the boiler characterizes the degree of technical equipment, the net efficiency - the efficiency of fuel consumption.

To identify boiler efficiency indicators, the formula is used:

Boiler efficiency = (Q1/ Q_total)x100%, where Q1 is the accumulated heat used for heating, and Q_total is the total amount of thermal energy released during fuel combustion.

The calculations do not cover many points, so their results are averaged. Any failures or deviations in the operation of equipment or external factors, affecting heat loss, will distort the result obtained from this formula.
In order to exclude larger number distorting factors, the result is corrected to clarify the thermal efficiency. Depending on the features specific system heating.

Boiler efficiency=100-(Q2+Q3+Q4+Q5+Q6)

Where Q2 is heat loss in the form of smoke released through the ventilation system,
Q3 – insufficient combustion of the gas mixture with incorrectly used volumes gas-air mixture,
Q4 – thermal heat loss due to contamination of the heat exchanger, as well as if the gas burners are dirty,
Q5 – heat loss due to external cold air (affects the performance of the boiler installation),
Q 6 – heat loss during cleaning of the combustion chamber.
The main factor influencing body efficiency is the exhaust waste combustion products; by reducing their heating within 10-12°C, the overall efficiency of a gas heating boiler can be increased by several percent.

For the same reason, condensing boilers have the highest efficiency index, i.e. the lower the temperature heating equipment, the higher this value. It has the lowest indicator due to minimal functionality and simple device.
The two options used in determining the efficiency of gas heating boilers are: reporting over a specific period of time and during initial installation tests. In the latter version, the calculation result will be more accurate, thanks to the clarity in calculating heat loss.

How to increase the efficiency of a gas boiler

Create suitable conditions To increase efficiency, you can optimize processes yourself or with the involvement of a specialist. Initially, all parameters are included in the design of the electric boiler; the effectiveness of measures taken to increase the efficiency of the equipment will depend on these data.

To begin with, modernization is carried out without changing the structure of solid fuel boilers:

Room thermostats. They control the temperature in living spaces without affecting the operation of the coolant.
Installing a circular pump, this way you can stabilize the uniformity and speed of heating.
Replacement gas burner, will increase the efficiency of a solid fuel boiler by 5-7%. A modulating burner will allow you to consume the gas-air mixture in the correct proportions, which will eliminate incomplete combustion.
Placing the burners near the water circuit will add to total number Efficiency is several percent. Such a partial modification will have a positive effect on fuel consumption and increase the thermal balance of the entire system.

Carrying out regular maintenance and cleaning equipment will increase its efficiency. Scale in the pipes of the heating system and soot on the outer walls of the chimney, formed during operation, can take up to 5%. Plastic pipes They require less maintenance, but they need to be purged periodically.

A clogged chimney narrows the passage of the smoke exhaust pipe, this leads to a decrease in draft, and this is not only a loss of heat, but also a threat to the health of people in residential premises.

Also, a heat exchanger with visible signs of contamination, which are salt deposits of metals, provokes a high consumption of all types of energy spent on work, which reduces thermal conductivity and can damage the boiler. Cleaning the combustion chamber is mandatory and is carried out several times a year.

As an option to reduce chemical heat losses, a highly qualified equipment system is configured for this. It is better to refrain from setting it up yourself and entrust the matter to a specialist.
The fight against food shortages can be solved by increasing the rate of delivery liquefied gas into the burner, so the combustion process occurs more actively, and the efficiency, accordingly, increases.

Although an increase in efficiency has practically no effect on the thermal efficiency of the boiler unit. Today natural gas remains the most economical, equipment using this fuel is more common and economically justified than boilers using traditional solid wood fuel or coal.

Gas boilers with the highest efficiency

The best quality boilers, which also have high efficiency rates, are of foreign origin. Energy-saving technologies that meet EU requirements are decisive in the production of such equipment.

Provides high performance modern instruments modernization, for example, like modulating burner.

Automatic and economical, it has a wide range that allows you to adapt to the individual parameters of a particular boiler and heating system. Its combustion is carried out in a constant mode.
Also, the main advantage is their maximum heat transfer. Most optimal value heating the coolant, provided by a foreign manufacturer, to 70°C. Combustion products heat up to no more than 110°C.
They make a heat exchanger for boilers with the highest efficiency indicators from of stainless steel. Additionally, they are equipped with a block for extracting heat from condensate. Disadvantages that are typical at low temperature heating: the traction force develops with insufficient force and the formation of excessive condensation.

The supply of already heated gas and gas-air mixture to the burner, as well as air entering the chamber through a double-cavity pipe into the firebox, ensures a reduction in the total heat input for boilers closed type by 1-2%.

Good option modernization of the boiler unit consists of installing exhaust gas recirculation. With this option, the combustion products enter the burner device after passing through the chimney channel with strong kinks, while being enriched with oxygen from external environment. Maximum efficiency is achieved at a temperature at which condensation forms (dew point).

Condensing boilers, operating under heating conditions at low temperatures characterized by relatively low gas consumption. This determines their thermal efficiency, especially when connected to gas cylinder installations. This also makes such a boiler economical.
List of condensing boilers known and honored European manufacturers With best quality assembly and high level Efficiency:

Baxi.
Buderus.
De Dietrich.
Vaillant.
Viessmann.

As stated by their manufacturers in the accompanying documentation, the efficiency of these boiler units, when connected to low temperature systems, corresponds to 107-110%.