In the modern world, great importance, especially in recent years, has been given to the problems of heat and energy saving. This is connected both with issues of saving resources and with a reasonable attitude towards the environment. An effective way to combine such “green savings” was the use of waste heat recovery and utilization methods.

Just a couple of years ago, these methods were used only in large industries, but today environmentally friendly and economical devices are available to the average consumer. These issues are especially important in the field of individual heating. So scientists created gas condensing boilers.

What is the essence of this technology?

As you know, when natural gas is burned, steam is produced, which has a small amount of energy. So, this energy can be extracted. In conventional gas boilers, steam and exhaust gases simply heat the coolant and are discharged outside.

Condensing boilers are equipped with an additional circuit where additional selection of this “unnecessary” heat occurs. All combustion products are cooled to a temperature of about 55 degrees, at which the process of water condensation occurs.

During the condensation process, latent heat is released and transferred to the coolant. It turns out that such a gas condensing boiler will work both more efficiently and economically.

The main advantages of this unit are:

1. In terms of high efficiency, which is about 109%, no gas device can boast of such an indicator.
2. A condensing boiler consumes 20% less fuel (compared to a conventional appliance).
3. The device may have a lighter plastic chimney due to the fact that the gases leaving the boiler have a low temperature (40°C).

As for the disadvantages of this type of boiler. Condensing gas appliances require a condensate drainage system. Sometimes difficulties arise with this, especially when choosing a gas wall-mounted boiler. After all, it will be difficult to connect it to the sewer system to remove condensate.

And another drawback is the low temperature of the coolant. It will be necessary to calculate other heating elements that have greater power.

Condensing boilers - video review

Distinctive features of the technological device

In addition to all their advantages, condensing boilers also have design features. Their heat exchanger is made of reliable high-quality steel, and in the heat exchanger itself there is a spiral with small holes that allow heated gas to pass through.

Another “highlight” of this type of heating is the burner. It is here that the gas is enriched with oxygen, due to which the entire fuel volume is effectively burned. Such a burner was invented to remove vapors released by condensate and harmful substances that can cause corrosion of the heat exchanger.

Gas condensing models, like classic heating units, can be single- or double-circuit. That is, serve only to heat the house, or also perform the function of heating water. Condensing boilers also differ in the installation method - they can be wall-mounted or floor-mounted.

Wall-mounted heating boilers

Such models are popular as a boiler with a boiler, since most often these condensing boilers perform two functions at once - heating water and heating. This equipment will have a heat exchanger installed with a special high-performance rod.

Which manufacturers offer condensing wall-mounted and technological boilers?

Beretta heating boilers – Italian representatives of boilers from a well-known company. The price of the cheapest unit will be 570 USD. such a model will have a power of 11 kW, an automatic ignition system, temperature control and the ability to self-diagnosis.

Beretta gas boilers differ in several other features:

1. Equipped with cast iron parts, which are produced specifically for Italian boilers.
2. They are equipped with burners for operation on gas and gas-diesel fuel.
3. Equipped with the ability to adjust the temperature.

Lamborghini wall mounted boilers – these condensing gas appliances are highly powerful, and most of the devices are equipped with an aluminum heat exchanger. The price of Lamborghini boilers starts from 2100 USD. – this is how much a condensing unit with a power of 53 kW will cost.

The boilers also differ:

• The presence of a relay that controls the flow of gas.
• Electric ignition system.
• The presence of a thermostat that reacts to poor draft and turns off the device in case of danger of smoke.
• Availability of “winter/summer” operating modes.

Floor standing boilers

Such condensing models are designed for a large area and, as a rule, they have increased power (compared to wall-mounted models). Most often, floor-standing gas boilers are made in a single-circuit version - they serve only for space heating.

Due to the increased power, the price of floor-standing models is sometimes higher than that of dual-circuit models. This is due to the fact that the floor heating condensing boiler has taken root most of all in large houses - it works more efficiently and consumes less fuel than a classic appliance.

Floor-mounted powerful condensing boilers are available from several brands, but the most “strong” are models from Baxi and Viessmann.

Floor-standing boilers from Baxi and Viessmann are designed for heating a large house - their power is up to 65 kW, which is enough to heat a house of 650 square meters. Of course, the price of such a unit will be about 3000 USD.

But this is not the only reason for this price; in addition, Baxi and Viessmann gas condensing boilers are equipped with:

1. Steel heat exchanger.
2. Electronic pressure gauge.
3. Antifreeze system.
4. Touch control panel.

How to choose a condensing device?

Firstly, it is worth saying that a gas condensation heating boiler, although more expensive than other appliances, will pay for itself in fuel savings in a couple of years. In addition, a condensing boiler will consume gas much more economically and heat a large house more efficiently.

It is worth choosing the optimal model based on general parameters - installation method, power and the presence of automatic and protective systems.

• A boiler with a power of 25 kW will cope with heating a house of 150-180 square meters.
• A medium-power device can heat water up to 60 degrees.
• The average water heating rate of a heating boiler is 10 liters of water will heat up to a temperature of +25 °C in one minute.
• The optimal gas consumption for a home is 100-160 sq. meters is 2.7 cubic meters/hour.

Owners of private housing construction are interested in cheap ways to heat their homes in winter. Condensing gas boilers that have recently appeared on the market have the highest efficiency among analogues. In addition, with their help, they save from 10 to 35% of energy, which has a positive effect on the consumer’s budget.

Principle of operation

This unit is designed on the basis of a conventional (convection) heat generator. The energy source for both types of boilers is natural or liquefied gas.

The operating principle of a convection boiler is extremely simple. When fuel burns, it transfers energy to the coolant (most often ordinary water) through a heat exchanger. The heated water circulates through the heating system, warming the home.

Combustion products at a temperature of 140–150°C, consisting of carbon dioxide and water vapor, are removed through the chimney. As a result, the efficiency of this heat generator ranges from 90 to 93%, the remaining 7–10% of unused energy evaporates into the atmosphere.

It is important! When the flue gas temperature is below 140°C, condensation forms on the walls of the chimney, which, when it enters the boiler, negatively affects metal components, reducing the durability of the unit itself.

Differences in the operation of conventional and condensing boilers

In a condensing boiler, the combustion products, having passed through the main heat exchanger, enter the after-cooling chamber with a secondary (condensation) heat exchanger, through which cooled water (return) moves. Passing through this heat exchanger, the gases cool down. At temperatures below 56°C (dew point - vapor condensation temperature), water vapor is converted into condensate. The thermal energy released in this case is used to preheat the “return”. The temperature of the gases entering the atmosphere through the chimney is reduced to 40–60°C.

Thus, slightly heated water enters the main heat exchanger. As a result, the boiler needs to spend less fuel to heat the coolant to the required value.

Manufacturers claim that the efficiency of these units reaches 104–108%. From a physics point of view, this is impossible. This meaning is conditional and is a marketing gimmick. In this case, 100% efficiency is taken to be the energy released during fuel combustion.

Scheme of formation of efficiency in gas boilers.

Wall-mounted boilers are used to heat small detached buildings.

Floor-standing

The power of floor-standing units reaches 1000 kW. They have large dimensions and weight. Space is required to install additional equipment and place the harness. A separate room is usually allocated for them.

They are characterized by simplicity of design and complexity of installation. Used for heating industrial and commercial buildings with large areas.

Floor-standing boilers are installed in large rooms

According to their purpose, condensing boilers are divided into double-circuit and single-circuit.

Dual-circuit

In addition to heating the room, a hot water supply system (DHW) is supplied with water. For this purpose, the boiler is equipped with an additional heat exchanger. In addition, a three-way valve is installed in the boiler, which regulates the flow of water into only one of the systems. When using hot water for domestic purposes, the valve automatically stops the supply of coolant to the heating system, as it is set to DHW priority.

The performance of the DHW circuit is relatively low. Turning on hot water at several points simultaneously quickly leads to a decrease in its temperature.

The use of double-circuit boilers is advisable when hot water is consumed infrequently and in small volumes.

Single-circuit

Intended for room heating only. However, many models provide the ability to connect an indirect heating boiler to the boiler - a storage tank that automatically maintains the required temperature. Its volume is selected depending on the owner’s needs for hot water. This allows you to use hot water for your own needs without restrictions, without turning off the heating system. It is convenient to install a single-circuit boiler in a house with three or more residents.

Advantages and disadvantages of a condensing gas boiler

Due to the large number of advantages compared to conventional boilers, condensing heat generators are increasingly popular among the population. But these units also have disadvantages that must be taken into account.

pros	Minuses
Small dimensions and weight (wall-mounted)	High purchase price
High efficiency	Efficiency and feasibility of operation only in low-temperature heating systems
Flexible modulation according to the required parameters	The need for disposal or neutralization of condensate
Energy savings up to 35%	High sensitivity to supply air quality
High environmental friendliness
Low noise and vibration levels
Low exhaust gas temperature
Ease of installation (wall-mounted)
Saving on chimney installation

Popular brands

Having decided to purchase this type of heat generator, it is better to pay attention to modern, reliable models from well-known manufacturers.

"Buderus Logamax Plus GB172i" (Germany)

Wall-mounted condensing boilers of a new generation with a power from 20 to 42 kW, embodying the latest developments in the world of heating engineering. They have excellent performance characteristics and modern design:

• Standard efficiency - 109%;
• Impact-resistant Titanium glass is used to make the front panel;
• Highly efficient long-lasting heat exchangers WB5 and WB6 made of ALU plus aluminum alloy;
• Built-in pump with class A energy efficiency;
• Burner with increased efficiency, modulation range - 1:8;
• Automation "Buderus Logamatic BC 25" with the ability to integrate additional automation to expand functionality;
• Availability of weather-dependent mode (burner operation relative to external or internal temperature);
• Work on antifreeze;
• Branch pipe for coaxial chimney 80/125;
• Possibility of adding automation “Buderus Logamatic TC100” or “Logamatic web KM200” to control the operation of the boiler via the Internet;
• Energy efficiency class - A.

Buderus boiler models

There are double-circuit and single-circuit models. An indirect heating boiler can be connected to the latter.

Price – from 88,000 rubles.

"Viessmann Vitodens 100-W" (Germany, Türkiye)

Models in this line are a good combination of high efficiency, reliability and price.

Available in power ratings from 19 to 35 kW.

Viessmann Vitodens 100-W boilers, operating on liquefied and main gas, are ideal for heating private homes and office premises:

The price of models running on liquefied gas is from 76,000 rubles.

The price of models operating on main gas is from 96,500 rubles.

Vaillant ecoTEC plus VU OE (Germany)

This range of single-circuit boilers is environmentally friendly and economical. The power of manufactured units is 30–65 kW.

Ideal for low temperature heating systems:

• Nominal efficiency - 108%;
• Simulated burner with a wide range of 28–100%;
• The primary and condensing heat exchangers are made of stainless steel with increased corrosion resistance;
• Environmental friendliness;
• Automatic air vent;
• Two-stage circulation pump with automatic switching;
• Fan with adjustable speed;
• Integrated expansion tank;
• Siphon for condensate drainage;
• System for increasing the efficiency of the condensing heat exchanger “Agua-Kondens”;
• Electronic ignition;
• Flame control system;
• Built-in switching module for interface;
• Smoke exhaust pipe 60/100 mm.

For the DHW system, an indirect heating boiler is connected.

All Vaillant models have a degree of protection IPX4D.

Price - from 91,500 rubles.

"Baxi Duo-Tec Compact" (Italy)

The line is represented by a single-circuit boiler with a power of 24 kW and two double-circuit boilers with a power of 24 and 28 kW.

They are distinguished by the implemented advanced technologies, ease of installation, operation and maintenance at a low price:

• Nominal efficiency - 109%;
• Conversion to liquefied gas;
• Primary and secondary (double-circuit) heat exchangers are made of AISI 316L stainless steel;
• Steel burner with modulating ratio 1:7;
• Flame control system with ionizer;
• High energy saving circulation pump;
• Built-in automatic air vent;
• Electric three-way valve (all models);
• Operating mode relative to built-in weather-compensating automation;
• Control of separate different temperature zones;
• Protection systems against overheating, freezing, blocking;
• NTC sensor that monitors the level of pollution in exhaust gases;
• Self-diagnostic electronics.

If necessary, an indirect heating boiler is connected to the single-circuit model.

Gas boiler "Baxi Duo-Tec Compact"

Price - from 50,500 rubles.

The described models have gained popularity due to their efficiency, impeccability, and reliability of operation.

Vaillant ecoCOMPACT VSC INT

Gas condensing boilers are the latest technology in the heating technology category. Their main advantage over traditional appliances is their high efficiency, which is 15–20% higher than that of conventional boilers. But high efficiency is observed only at low-temperature operating conditions of the heating system.

And that is not all.

Features of condensing boilers

Such units can provide heat to additional branches, for example, a “warm floor” system. Plus, their service life is 2 times longer than that of traditional models, and the range of power and configuration is wider. Such mounted boilers can have a power of up to 100 kilowatts, while conventional boilers can have a power of up to 35 kW.

Why do conventional boilers have low efficiency? To understand this, you need to understand the design of the device. In such units, thermal energy is collected in fairly large quantities, but not all of it is used to heat the coolant, since there are losses. In addition, under certain conditions, condensation forms on the heat exchanger. This leads to corrosion of the metal from which the heat exchanger is made. So the service life of such a boiler is several times shorter.

Why does condensation appear? It's all about the temperature inside the heat exchanger. It should not fall below a certain indicator. If this happens, the draft in the chimney weakens, and wet vapors begin to deposit on the metal parts of the boiler. With sufficient draft, wet vapors are promptly removed from the combustion chamber. This is the whole problem with conventional gas boilers.

In condensing boilers, a recovery process operates when latent thermal energy is extracted from condensing wet vapors generated during the combustion of natural gas. And this is a distinctive feature of such boilers.

If we consider the individual components of any boiler, its main element is the heat exchanger. In ordinary boilers there is one, but in condensing boilers there are two. Moreover, they can be separate or combined - two-stage. The primary heat exchanger in condensing boilers works the same as in conventional ones. That is, the heat from the combustion of fuel passes through it, heating its surface, and therefore the coolant that moves through the internal cavities. By the way, the primary coolant never cools down to the dew point temperature. The second heat exchanger is heated by the same gases, but coolant from the return line flows through it.

Boiler structure

Now notice that the water in the return line is much lower than in the supply line. This means that wet vapor will certainly condense on the surfaces of the heat exchanger. But at the same time, latent thermal energy from the condensation process will be added here. That is, when a substance transitions from a vapor state to a liquid state, heat is always released. This is a law of physics. This is why the efficiency of condensing boilers is several percent higher than that of conventional boilers.

But here one very important question arises - how to cope with the negative effects of moisture that will form on the walls of the secondary heat exchanger? Experts offer two options:

1. Make a heat exchanger from stainless steel.
2. Coat a cast iron or steel device with silumin, an alloy of aluminum and silicon.

Where does the condensate go?

This question is often asked by consumers who have decided to purchase a condensing boiler. The design of the heating device has a small reservoir where condensate is collected. From there it is discharged into the sewer. By the way, in Europe it is prohibited to pour such water into the sewer. Each consumer must dispose of condensation waste at his own expense. These are the strict requirements.

Vaillant ecoCOMPACT

How much condensate is formed, for example, per day? If you take a 30-kilowatt floor-mounted condensing gas boiler, it will produce about 30 liters of condensate per day. The volume is considerable, which is why Europeans do not give permission to drain all this into the general sewer system. True, today models have appeared on the market with a neutralizer built into their design. This is a new tank filled with magnesium and potassium granules, which are alkali metals. The acidic condensate passes through an alkaline environment, causing a chemical reaction. As a result, the final products are formed - carbon dioxide and water. This water can now be poured into the sewer.

And now a few words about the maximum efficiency of the condensing unit. If you purchase this model, but leave the old heating system, where there is no radial piping, do not complain that there will be no savings. After all, such a boiler will work effectively only during the warm-up period, and then everything will go according to the old scheme. Therefore, my advice is to immediately change the wiring diagram. This is the first.

Secondly, the temperature difference at the boiler outlet and inlet must be at least 55 degrees. In this case, the optimal temperature of the coolant at the outlet should be +82C. And this is with natural circulation of hot water inside the heating system.

History of devices

Boiler room in the house

These boilers appeared back in the 50s of the last century. The first models were unreliable because they quickly failed under the influence of acid condensate. In addition, in different European countries there was no uniform standard for gas mixtures used to heat the coolant. That is, there was a problem on top of a problem. Everything changed in the 70s, when stainless steel began to be used for the production of secondary heat exchangers.

Today, in almost all European countries the state supports the installation of condensing boilers. For example, banks issue loans with the lowest interest rates for its purchase.

Alternative point of view

One hundred percent efficiency is a bluff of advertisers. But manufacturers of heating equipment, including gas boilers, are trying to achieve maximum efficiency. It should be remembered that this indicator depends on many factors:

• From the age of the heating unit.
• The relationship between the power of the boiler and the volume of the room it heats.
• Using a modern type of ignition or old options.

Currently, manufacturers offer two types of condensing boilers - with wet and dry heat transfer. Units with dry heat transfer are boilers that are used in residential premises, that is, they are ordinary condensing devices. Units with wet heat transfer are used mainly in commercial boiler houses and are still under development. They are more effective, but much more expensive.

Benefits from condensation

Schematic diagram

All boilers that are installed in small private houses have the ability to change power by regulating the gas supply to the burner. In this regard, condensing boilers are in no way inferior to their conventional counterparts, but their maximum operating efficiency is observed at lower temperatures. That's the whole difference. But not only.

What is the relationship between boiler power and coolant temperature? The more powerful the boiler, the more fuel it consumes, and the higher the coolant temperature. And vice versa. Most often, the efficiency, and therefore the operating efficiency of the heating unit, depends on the fuel supply. The more of it, the better.

In condensing boilers everything is different. Their maximum efficiency is observed when the boiler is loaded at only 30%. In this case, there is no point in choosing from a low-power or more powerful unit, since this indicator does not matter.

By the way, experts believe that a “warm floor” system works well with a condensing boiler:

• The temperature of the coolant in both the supply and return of the heated floor is always below the condensation level of wet vapors. This barrier is +56C.
• The underfloor heating system contains a fairly large volume of water, which has to be heated for a long time. That is, the burner operating cycle at low temperatures with minimum power increases. This means that more time is spent on the condensation process.

If we compare it with a simple boiler, the coolant quickly heats up, the burner turns off, and vapor condensation does not occur. The decrease in efficiency is obvious.

Chimney for boiler

Baxi Coaxial

It is clear that condensing boilers release combustion products at a low temperature, which means that the draft in the chimney will be weak. Combustion products cannot rise up the chimney naturally, so in such models the combustion chamber is closed, and fans are installed on the chimney. By the way, it is for such boilers that a coaxial chimney is installed - a pipe in a pipe. The internal fan removes fuel combustion products, and the external fan draws air from outside into the combustion chamber.

Please note that condensation will certainly form in the chimney itself, whether you like it or not. Therefore, it is made of acid-resistant steel. And if the house has a brick chimney, then its internal walls must be lined with the same steel. This is a prerequisite for the correct operation of condensing boilers.

Advantages and disadvantages

The advantages of such units include the fact that during a long winter, when the average temperature is -20C, they work much more efficiently than their conventional counterparts. In addition, with proper operation, natural gas savings occur by at least 15%. And if you compare it with old models, then by 30%. In addition, these models are the least harmful to the environment because they emit a minimum of CO and other gases.

Buderus Logano plus SB615

But they have only one drawback - their high price. And if we compare again, the difference with conventional units will be no less than 2 times. If we consider the situation from an economic point of view, then such heating units will pay for themselves faster where the need for heat is greatest. Therefore, the deficiency can be transferred to another category. We will assume that this is direct investment, because the increase in gas prices is obvious. And no one knows what its price will be in 5 or 6 years. And savings are constant, so there is no need to skimp when choosing the latest technologies.

Conclusion on the topic

New heating technologies are gradually entering our lives. And it is clear that the manufacturer who supplies the market with highly efficient units at an affordable price will win. We will not say yet that gas condensing boilers have an acceptable price, but this is just the beginning. Just a few years ago, few people knew about these boilers, but now they are quite popular. And most importantly, consumers are looking less and less at price, realizing that savings of even 15% are a good indicator.