A double-circuit boiler gives a certain independence from central heating and allows you to always have hot water in the house. Although in general, double-circuit models are somewhat more expensive than single-circuit ones, their purchase can be more profitable, since it also allows you to replace the boiler. Which is the best wall-mounted double-circuit gas boiler to buy for your home? We will tell you what important criteria you should pay attention to when choosing and give a rating of double-circuit wall-mounted gas boilers in 2022.
What to look for when choosing?
Before purchasing a dual-circuit model, you should pay attention to five important indicators:
Combustion chamber type
There are devices with an open and closed combustion chamber. Appliances with an open chamber take air from the room, and combustion products are discharged through the chimney. For safety reasons, such a chimney must be at least 4 m in height. Since this consumes oxygen from the room, ventilation in such a house must be well organized.
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With closed combustion, air is taken from the street, and combustion products are discharged outside at this moment. Thus, the oxygen in the room does not burn and the overall atmosphere is much more favorable. Models with a closed chamber are suitable for those who have poor ventilation in their home. They can also be installed in the kitchen or bathroom. Devices with a closed combustion chamber are the only possible option for apartment buildings.
Boiler type
There are classic (convection) and condensation devices.
Classic wall-mounted gas boilers with two circuits, the 2022 rating of which will be given below, generate heat only by burning gas. On average, their efficiency ranges from 85 to 95%.
Condensing appliances generate additional heat by condensing water vapor that is produced naturally during the combustion process. Thanks to this, the boiler efficiency increases and can range from 100 to 110%. Taking this into account, the condensing model can reduce gas consumption by 10 - 15%. This savings will be especially noticeable when using heated floors. If you really want to save on heating and water heating, then take a condensing model. Such models will definitely be included in our rating of wall-mounted double-circuit gas boilers in terms of reliability.
Heat exchanger material
The heat exchanger of the device can be made of the following materials:
- Cast iron . Used in the cheapest models. It generates heat quite well, but the efficiency usually does not exceed 90%. Boilers with cast iron heat exchangers are heavier and bulkier, which complicates their installation.
- Stainless steel . Suitable for budget and middle class. Stainless steel is quite durable and can be easily repaired if necessary. However, heat transfer is less than that of copper.
- Copper . Copper heat exchangers are installed in mid- and expensive-class models. They are durable and dissipate heat well.
If you want to take a classic model and are going to install it yourself, take it with a stainless heat exchanger. For underfloor heating and hot water supply, we recommend choosing a condensing type device with a copper heat exchanger.
Boiler power
On average, 1 kW of device power can heat about 8 m2 of area. Divide the total area you need to heat by 8 and get the required power. Add 1 kW for water heating. If you want to more accurately calculate the power of the device, use the formula that we provided for single-circuit boilers.
Availability of built-in boiler
A separate type of double-circuit boilers can be additionally equipped with a boiler for heating and, most importantly, storing water. Sometimes it is very convenient to have such a boiler, since if there is a strong drop in pressure in the pipeline, the boiler may simply not heat the water, but the water in the boiler will always be hot. Purchasing a model with a built-in boiler makes sense only in cases where there is a frequent drop in pressure in the city water supply. Otherwise, it's a waste of money.
Automatic power simulation
The purpose of using automation is to ensure the supply of the right amount of fuel and air, which will lead to optimal compliance with the thermal conditions of the users. As a result, the solution leads to lower heating costs.
Automation allows for optimal performance. This is especially important given the need to select a boiler in such a way that it can operate in difficult weather conditions, especially in spring and autumn.
Constantly turning the boiler on and off manually over time leads to inefficient operation and at the same time can lead to more wear and tear. The goal of this solution is to provide the optimal amount of heat, neither too little nor too much.
Top best convection wall-mounted double-circuit gas boilers
Vaillant Turbo Fit VUW
A good double-circuit boiler of Turkish assembly, but from a German manufacturer. The Fit model in this line has been in production for two years now and most users have not had any problems with it during this time. A 24 kW boiler is capable of heating up to 192 m2 of area. The maximum temperature of the coolant in the heating system is 80° C, and the water in the hot water supply is 64° C. A high-quality primary copper heat exchanger is installed here, which contributes to the delivery of up to 93.5% efficiency. The secondary heat exchanger is made of stainless steel. An expansion tank of 7 liters is installed for the primary circuit.
One of the main advantages of the boiler is the presence of a closed combustion chamber. Due to the fact that air is taken from the street, and not from the room, a comfortable atmosphere is maintained in the room. The maximum natural gas consumption is 2.66 m3/h (at a maximum power of 24 kW). All boiler control is carried out using several buttons on the body and a mechanical power regulator. Please note that the device must be grounded. If this does not happen, the accumulated static electricity can trigger an EA error (the flame sensor does not see the flame).
BAXI ECO-4s 18F
The 18-kilowatt unit does an excellent job of heating 144 m2 of area and heating hot water. This single-phase convection type boiler produces an efficiency of up to 92.5%. At the same time, like the Vaillant Turbo Fit, it has a primary copper heat exchanger and a secondary stainless steel one (for hot water supply). There is a turbocharged (closed) combustion chamber, so the boiler can be easily installed in small rooms, such as a bathroom or kitchen, or rooms with poor ventilation. The model has a so-called summer operating mode. When this mode is started, the circuit that goes for heating stops functioning, and the boiler only works to heat water. In addition, the unit can be connected to a “warm floor” system.
The device is equipped with protection systems against gas pressure drop and flame extinction. In both cases, the gas supply stops and the gas valve is completely closed. To resume operation, you will have to turn it on manually. The thermostat can be programmed not only by hour, but also by day of the week, defining the operation of the boiler individually for each day. When the coolant in the heating system cools below 5° C, the sensor starts the burner, preventing the water from freezing. Please also note that the manufacturer also included a water filter in the kit (for most models you have to buy it separately).
Ariston ALTEAS X 24 FF NG
This model can be safely called smart, as it can be controlled from a smartphone or tablet. For example, you can program the unit to turn on and off by day and even by hour. You can also monitor the temperature of the coolant in heating and hot water supply pipes. The boiler can be integrated into the Ariston NET smart home system. The power of the device is 24 kW, which allows it to efficiently heat up to 192 m2. The device is equipped with a “hot start” function, which speeds up the heating of water for the hot water supply system and ensures a constant outlet water temperature.
As in the two previous units, there is a closed combustion chamber and a forced smoke removal system, in which the main working element is a centrifugal fan. This allows you to install it directly in residential premises. The frost protection system will start the boiler if the water temperature in the pipes drops below 5° C. Users note that the unit is quite quiet in operation and easy to install. However, such high quality workmanship and the “smartness” of the boiler affected its rather hefty price.
Advantages and disadvantages
Advantages:
- ease of installation;
- aesthetic appearance;
- ease of use;
- silent operation;
- the ability to set the required temperature;
- fire safety;
- no exhaust gases emitted.
Flaws:
- inappropriate use for large rooms due to high energy consumption;
- reduction in the efficiency of the device due to constant power outages or power outages;
- the need to change the wiring, because old wires may not withstand heavy loads.
The best condensing dual-circuit models 2022
Protherm Lynx 25/30 MKV
The Slovak-made condensing model is capable of heating up to 212 m2 and produces approximately 14.2 liters of hot water per minute. This performance is quite enough to provide two water points - for example, a kitchen and a bathroom. There is a turbocharged closed combustion chamber here, so there will always be enough oxygen in the house (more precisely, the boiler will not burn it). Like the Ariston model, Lynx is equipped with a “hot start” function, which speeds up the heating of water in the water supply system. There is also a sensor installed here that switches the device to summer mode during the warm season. In this mode, the unit only works to heat water.
The efficiency of the device, thanks to the receipt of thermal energy from steam, is 104%, which is approximately 9% more than that of conventional convection models. The manufacturer has equipped the model with protection systems against freezing and water overheating. The first controls the temperature of the water in the heating pipes and, when it drops below 5° C, starts the boiler to avoid the formation of ice. The second turns off the device when the critical water temperature is reached. Overall, this is an excellent boiler for the money, which works one hundred percent.
BAXI Duo-Tec Compact 28
This unit is designed for a large house up to 224 m2. Its efficiency is slightly higher than the previous one and is 105.8%, which, compared to conventional convection ones, gives about 11% savings on gas. The second circuit is capable of heating up to 16.1 l/min of water, which is enough to operate a shower stall, washbasin and sink. A turbocharged combustion chamber and a forced smoke exhaust system will help maintain a comfortable atmosphere in the apartment. Both heat exchangers are made of stainless steel. Please note that the boiler design is equipped with an outside temperature sensor. It monitors the temperature outside the window and, in accordance with it, reduces or increases the power of the unit.
You can safely connect a heated floor to the device, since there is a powerful circulation pump. It allows you to effectively pump water through a circuit with high resistance. If the water circulation is disrupted, the device turns off the gas supply to the burner, as well as the pump itself, to avoid damage to these components. There are also systems installed here to protect against freezing and overheating of water in the pipes.
Bosch Condens GC7000iW
This model in the Bosch line of condensing boilers is one of the most economical. It can operate on both natural and liquefied gas. Its efficiency is as much as 108% - this is 13 - 15% better than convection devices. When you connect the Easy Control control panel, you can control the device via the Internet. This is very convenient, since you can receive a report on the operation of the boiler or generated errors even while at work. The unit can work with both water and antifreeze specified in the passport documentation for the device.
The design of the device is equipped with a 5th generation aluminosilicate heat exchanger with a matrix burner. There is also a 12 liter expansion tank. The maximum productivity of hot water at a temperature of 30 ° C is about 12 l/min - this is enough for two water points. A pressure gauge is installed on the front panel to visually determine the operating pressure. This is a high-quality, durable German-made boiler for heating and hot water supply. But as you know, you have to pay for quality, and this truth is confirmed by the rather high price of this unit.
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