Two-circuit gas boilers are the best way to heat private homes and prepare hot water. They work on the basis of transferring the energy generated by the combustion of the most affordable and popular type of fuel to the heat transfer medium. However, because of the wide range of equipment, it can be difficult to choose. Do you agree?
We will tell you how to decide on the most suitable model of a gas boiler. In the article we offer all the guidelines for choosing a unit with the highest possible efficiency, withstanding an intensive operational load. The leading models on the market and reliable manufacturers are listed.
- Design features of the unit
- What to consider when choosing?
- Site classification
- Floor type boilers
- Features of wall-mounted equipment
- Characteristics of parapet devices
- Differences of models according to their power
- Types of gas burners
- By types of ignition function
- Boiler draft versions
- Boiler with natural draft
- Force-operated Draft
- Distinguishing features of heat exchangers
- Benefits and disadvantages of gas systems
- Main advantages of the devices
- Disadvantages of dual circuit equipment
- Overview of popular manufacturers and models
- Conclusions and useful video on the subject
Construction features of the device
The household gas device consists of a body, two communication circuits, integrated burner, heat exchanger, expansion tank, combustion products outlet, gas valve and control unit.
The main circuit is connected to the common heating system in a closed circuit. When the unit is actively operating in heating mode, the heating medium circulates through the pipes of the first circuit and does not enter the hot water supply system (DHW) as a special valve blocks the way there.
When installing equipment with two circuits, it is mandatory to remember that the communication pipe length connecting the boiler to the farthest water intake point must not exceed 7 meters. Otherwise the mineral elements deposited as scale in the heat exchanger area will start to obstruct the flow of the working fluid and the water heater performance will be significantly reduced
When the user turns the hot tap in the kitchen or bathroom, the valve is activated, closes the heating pipes and directs the heating medium into the DHW circuit to heat the water in the heat exchanger.
From there the liquid flows into the tap and is used for its direct purpose. When hot water is no longer needed and the tap is closed, the valve is reversed and the heating medium is redirected back into the heating circuit.
What to consider when choosing?
All gas boilers of two circuits perform the same basic tasks but differ in such parameters as:
- power level;
- burner type;
- the ignition principle;
- the draft type;
- the heat exchanger material.
All the above criteria are of equal importance and require mandatory consideration when selecting and purchasing heating equipment.
Categorization by place of installation
Boilers serving two communication circuits can be floor standing, wall mounted and parapet mounted. Each variant has its own particular characteristics.
Based on these, the customer can choose the most suitable way of installation, in which the equipment will be conveniently located, will not \"eat up\" the useful space and will not cause problems during operation.
Floor type boilers
Floor units are high capacity units that can heat and provide hot water not only to a standard apartment or house, but also to a large industrial premises, a public building or a structure.
If a two-circuit boiler is planned to be used not only for heating and domestic hot water supply, but also for heating warm water floors, the basic unit is equipped with an additional circuit
Due to its large size and solid weight (up to 100 kg in some models) floor gas boilers are not placed in the kitchen but are placed in a separate room directly on the foundation or floor.
Features of wall-mounted equipment
The wall-mounted appliance is a progressive type of household heating equipment. Due to its compact size, the gas heater can be installed in the kitchen or other small rooms. It blends with any type of interior solution and blends seamlessly into the overall design.
Two-circuit hinged boiler can be located not only in the kitchen, but also in the pantry. It will take minimum space and will not obstruct the furniture or other appliances
Despite its small size, the wall mounted boiler has the same functionality as the floor standing boiler, but with less power. It consists of a burner, expansion tank, pressurized water pump, pressure gauge and automatic sensors which allow the best possible use of the fuel.
All communication elements are \"hidden\" under a nice, modern casing and do not spoil the look of the product.
The gas supply to the burner is controlled by a built-in safety system. In case of an unexpected interruption of the supply, the operation of the unit is stopped completely. When the fuel starts again, the automatics automatically activates the equipment and the boiler continues to operate in standard mode
Automatic control unit allows to set the appliance any operating parameters most suitable for the user. It is possible to set your own temperature regime for different times of the day, thus ensuring economical consumption of fuel.
Significance of the parapet units
The parapet boiler is a cross between a floor standing and a wall mounted unit. It has a closed combustion chamber and does not produce harmful emissions. It does not require an additional chimney. Flue gas is discharged through a coaxial chimney in the external wall.
The parapet type boiler is the best option of heating equipment for small rooms with a weak ventilation system. The appliance is designed so that during operation it does not release combustion products into the atmosphere of the room in which it is installed
The device is mainly used to provide hot water and full heating to small houses and apartments in multi-storey buildings where it is not possible to mount a classic vertical chimney. The basic output varies between 7 and 15 kW, but despite such low figures, the unit successfully copes with its tasks.
The main advantage of parapet equipment is the possibility to connect the heating and water pipes to the central gas system and pipelines from any convenient side.
Differences of models by power
Two circuit boilers are divided into one-stage and two-stage. Single-stage devices always operate at a constant output level and use the same amount of fuel throughout the year.
It is not efficient and leads to high gas consumption, as a house or apartment does not need high quality heating for more than 5 months a year. During the rest of the time it is not reasonable and economical to \"run\" the equipment at full capacity.
When installing equipment with basic capacity of 30 kW and more, you should know that these types of devices should not be located in living rooms but in separate rooms equipped with a quality ventilation system, individual exit to the street and a full flue
Functionality of two-stage devices is more wide.
- control the gas flow and rationalize the fuel consumption;
- reduce the number of switching on/off, thus reducing the wear of the equipment and prolong its lifetime;
- reduce to the minimum the harmful emissions into the air.
In addition, the device is equipped with a soft-switching module that reduces energy consumption and allows the simultaneous operation of a boiler and a boiler of any capacity, installed separately.
Types of operating gas burners
The gas burner is either atmospheric or supercharged. The first type has an elementary design and makes no noise in operation. It costs cheap and is usually included in the basic boiler package.
In spite of its simplicity, the atmospheric burner is very reliable and works well for a long time. It can be used both on budget appliances and on expensive, \"high-end\" luxury products
The operating principle of the atmospheric type burner resembles that of the industrial heated models. The fuel resource is fed through an ejector and by means of the draft it draws air from the surrounding atmosphere. Through a special hole the mixture enters the combustion chamber and is immediately ignited.
As a result above the outlets there are fiery flames with a very low actual temperature, whose task is to heat the heat carrier to the required level.
Hanging (hinged) burners show a high level of efficiency, in constant mode maintain a set temperature both in the heat carrier and in the hot water supply, but cost significantly more than their atmospheric analogues.
But these costs are justified, as the modules have an extended functionality and allow to use the fuel resource in the most reasonable way without reducing the comfort level of the house.
The blower (hinged) type is not included in the basic package of the two-circuit gas boiler. It is purchased separately and then installed on the heating equipment
In full operation in the supercharged burners the air supply is forced and its volume is very clearly controlled by the internal automatics. The module is placed in appliances equipped with a closed combustion chamber operating with a supercharger.
Fuel and air are not mixed inside the system, but at the outlet. The process of operation is almost fully automatic and does not require any human control.
Atmospheric burners are placed in double-circuit heating appliances up to 80 kW. Overhead units are used in big units with capacities up to several thousand.
Variants of the ignition function
The domestic split circuit boiler can be started manually (with matches or lighter) or with built-in elements (electric ignition or piezo ignition). The first method is the easiest and most accessible. The second one makes it possible to save the blue fuel, without leaving the wick in the igniter burning all the time.
The only disadvantage of this variant is the dependence on the electricity in the network. If the power fails for some reason, the equipment switches off immediately and automatically reactivates when the power returns.
Piezo ignition is absolutely safe and allows the boiler to be switched on by pressing just one button. It does not depend on power supply and you can use the appliance even in absence of electricity.
Equipment draught options
The fuel burns and smoke gases are produced during the operation of the unit. To remove them from the living space, a natural or forced draught is necessary. It ensures that all combustion gases and harmful substances are removed from the apartment or house in a timely manner.
Natural draught units
Natural draught boilers are designed in a simple way and extract the air necessary for proper combustion from the room in which they are installed. During intensive operation they emit a certain amount of steam and various chemicals. Emissions are extracted through a vertical chimney.
The main advantages of units with natural draught are reasonable cost, energy independence and no noise effects during operation
In general natural draught appliances are convenient and good, however, when the pressure in the gas line drops the quality of operation is significantly reduced. In parallel, the risk of quick burnout of the burner increases, as the flame dies out or escapes inside the burner when the pressure level drops.
Even pressure in the mains causes serious fuel overshoot, resulting in higher utility bills.
Forced draft appliances
Forced draft boilers are sometimes called blower or fan type. They do not take air from the room where they are located, but from the street. The modules have closed combustion chambers and the exhaust is carried out through a coaxial horizontal outlet with a powerful fan built into the system.
The coaxial outlet consists of two pipe elements of different diameters, inserted one into the other. Through the smaller pipe combustion products leave the room, and through the space between the small and large pipes fresh air, necessary for the full functioning of the boiler, enters the room from the street
Products with forced draft are easy to install, have no claims to the location, do not \"eat up\" oxygen in living rooms, work stably and clearly even at a reduced gas pressure in the central mains and do not need the arrangement of additional vertical chimney.
The devices are reproached by the noisy operation of fan elements, higher cost and dependence on electricity supply.
Defining features of heat exchangers
The heat exchange unit of the heating device is made of cast iron, steel or copper. The cast-iron version retains heat for a long time, is almost unaffected by corrosion due to the high wall thickness and shows resistance to aggressive heat transfer fluids. It has a high weight and therefore is mainly integrated into floor standing boilers.
Must be assembled with great care since any impact damages the structural integrity of the material and leads to the formation of micro cracks.
Steel construction has a low weight, not afraid of mechanical impact, easily tolerates temperature variations of the coolant, easy to transport and assemble. Has some tendency to corrode. To avoid it helps control the boiler system that does not allow the temperature of the coolant to drop below a critical point.
Copper elements are much more expensive than cast iron and steel counterparts, but offset the solid cost of a large number of advantages. Inside the copper heat exchanger, sludge and scale are formed to a minimum and do not interfere with normal circulation of the working fluid. The walls of the device heat evenly and do not cause local overheating of the coolant.
Benefits and drawbacks of gas systems
In places where central gas communications are laid, two-circuit boilers are very popular. They are purchased for heating and uninterrupted hot water supply in apartments, houses and country cottages.
Main advantages of devices
The gas system shows high efficiency level, gives away several times more energy than it consumes, serves long and works uninterruptedly. It does not need constant human supervision.
Two-circuit boiler looks neat and modern. Unlike solid or liquid fuel units, it emits almost no unpleasant odors during operation and produces a minimum of soot and soot
Fuel resource is fed to the unit continuously and the built-in controller independently monitors the presence of fire on the burner. If the flame goes out, the sensor sends a signal to the ignition unit and automatic sparking instantly restores the fire. The boiler control is elementary and presents no difficulty.
Disadvantages of two-circuit equipment
The main disadvantages are not so much related to the device itself, as to the process of its legalization and installation. You can not just buy a boiler, bring it home and install it with your own hands according to the connection diagram. First, you must observe a large number of technical details, complete the documentation and agree on all the arrangements with the local gas supply company.
There you must provide:
- the draft installation of the equipment, drawn up in accordance with the standards established by law;
- the contract for installation with a specialized organization;
- a copy of the license of the specialized organization, confirming the right to carry out works.
In addition, you will need to arrange for the exhaust of the gas from the accommodation, install an additional chimney or use an old one and install additional equipment for monitoring any possible gas leakage.
If the boiler smokes, the pressure in the system may have dropped or the existing burner may have worn out and begun to burn. A properly experienced specialist
The main installation activities can be started only when the project documentation for the gas heating organization has passed all approval stages and the client has received a sealed permit for installation.
Review of popular brands and models
The modern gas equipment market offers customers a large number of quality appliances designed for heating living spaces and hot water supply. They have extended functionality and serve reliably for many years. They meet the strictest European standards (confirmed by CSQ and UNI EN ISO 9001 certification) in terms of all parameters and physical characteristics.
Boiler with a basic output of 7 to 12 kW is suitable for small rooms (up to 50 sqm). If the area of the property is larger (for example 150-200 sq.m.) it is better to buy a 23-25 kW unit
Weak units simply cannot provide the apartment or house of large dimensions with full heating.
Buy floor gas boilers and wall mounted models only in company stores or official representative offices of manufacturing companies. There the customer will be told in detail about the principles of operation of this or that unit and will help to make the best right choice.
Conclusions and useful video on the topic
A simple and clear description of the basic principles of operation of domestic two-circuit gas boilers. Overview of the \"quick start\" and \"pump run out\" functions:
Expert opinion and some interesting things to look out for when choosing a boiler:
How wall hung boilers are constructed and how they work:
The targeted selection of a domestic dual circuit gas boiler for heating and domestic hot water is an important, responsible moment. Haste here is not necessary. It is better to think everything over in advance, decide on the brand and type of equipment, calculate the flow costs.
Consider the costs of purchase and installation activities, and then make a purchase in a specialized store. The manager will draw up the warranty papers and at the same time will consult the customer in detail about the operation of the device and the rules of safe operation.
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