How to choose a gas boiler and do not make a mistake? The easiest way to contact a consultant in a store or firm that installs heating equipment. The specialist will ask a few questions and recommend a particular model. However, it is difficult for an untrained person to understand how exactly the seller makes the choice. Suddenly, he did not consider something or advises not the best option? To be fully armed and learn to speak the same language as the experts, let’s understand the subtleties of choice.
One-and two-circuit boilers – what are they?
Two-circuit boiler or, as it is also called, combined is able to work not only for the heating system, but also to provide the user with hot water without installing additional equipment. This is a very convenient and compact solution, but it is necessary to take into account some details.
In the absence of water intake taps are closed , the boiler constantly heats water in the heating circuit, and when someone opens the tap, a special three-way valve switches the coolant flow to an additional heat exchanger of DHW. That is, during the use of the sink or shower heating of the coolant for the heating system stops. Such feature in a mode of work is caused by a design of two-circuit boilers and is called a priority on hot water.
If the house is big and hot water is actively used, then the boiler most of the time will be in the DHW mode, and the heating system will start to cool. Therefore, combined two-circuit boilers are recommended to install, for example, in cottages for a small family or in houses for periodic residence.
Another feature is the waiting time for hot water after opening a tap. Since the DHW system with a two-circuit boiler does not circulate, the water in it gradually cools. So it has to be drained every time, waiting until the hot water starts flowing.
This problem is solved in the wall mounted condensing boilers Viessmann Vitodens 100-W model B1KC . Their design includes the “combi-comfort” system, that constantly heats the DHW heat exchanger, which can significantly reduce the time of reaching the set level of hot water temperature.
Single-circuit boiler heats water only for the heating circuit. To be able to cook hot water, the boiler must be connected to an external boiler storage water heater . This equipment also has a priority on hot water, but unlike combined boilers, preparation is not instantaneous and limited by the area of the additional heat exchanger volume, but in a tank water heater in advance. This is more convenient, because there is a prepared necessary volume of hot water, maintained at a given temperature. The boiler capacity must be selected depending on the hot water requirement more on this later .
Two in one
A separate class of devices – boilers with a built-in boiler, for example, Viessmann Vitodens 111-W. Its capacity 46 liters is large enough to provide the need for hot water for a family of two or three people without stopping the heating fluid for the heating system. This is almost ideal for a cottage of up to 100-150 m2. However, this volume is not sufficient to supply hot water to a large house with several outlets, e.g. several bathrooms, a swimming pool, a whirlpool or a utility.
Do I have enough water??
So, with the types of boilers and the fundamental difference between them we have understood. The second important point – the demand for hot water. If it is not calculated correctly, it will not be very comfortable to live in the house.
In order not to miss the mark, you need to assume that at some point, all points of water can be used at the same time. On average a washbasin with a mixer tap or kitchen sink consumes 5-6 liters of hot water per minute, and a shower from 10 liters per minute. Two-circuit boiler Vitodens 100-W can cook from 12 to 16 liters of hot water per minute, and therefore can handle this volume. But,
e.g. three simultaneous open tap water points shower or bath + washbasin + kitchen sink can no longer be supplied by the boiler.
If we are talking about a country house, then you can put up with this small inconvenience, not using all the “amenities” at the same time. As for the house for permanent residence, it will be more appropriate to use the Vitodens 111-W, capable of serving from 16 to 20 liters of hot water per minute.
When the demand is greater, it is worth considering a single boiler with an external boiler. For example, the Vitodens 100-W B1HC allows you to connect water heaters with a capacity of 100, 120 and 150 liters, which simultaneously provide hot water for the shower and 2-3 sinks.
In addition, the scheme with an external boiler can be organized by recirculating water in the DHW system, that is, to solve the problem of waiting for hot water from the tap on the scale of a fairly large house, making it as comfortable to use as in a conventional city apartment. For the convenience of arrangement, there are different types of water heaters, such as stack boilers for placement directly under the wall-mounted boiler or separately standing vertical and horizontal.
And what should be the power of the boiler?
This is the third important point to consider when making your choice. Any including compact wall hung boilers with small capacity, such as Vitodens 100-W and 111-W, are available in several versions: their maximum capacity can reach 19, 26 and 35 kW. Is it a lot or not?
It all depends on the need for heat and hot water. First of all you need to take into account the thermal capacity of the heating system. That is why a boiler is never selected before the capacity is known. In an ideal case specialists make thermal and projection calculations of the system, which results in the required boiler output.
On average, to meet the heating and hot water needs of a cottage of 150 m2 for a family of three people requires 15-25 kW of thermal capacity, and for a house of 200-250 m2 – 25-35 kW. However, these data are approximate, so in practice it is better to make a more accurate calculation.
What kind of boiler is energy efficient?
It is of great importance how economically the boiler spends fuel, because the cost of it is the main item of household utility bills in an individual household. Here much depends on the type of burner.
Boilers with single-stage burners always operate at a constant output, so the automation frequently switches them on and off. From the standpoint of fuel economy this is the least preferable option, in addition, the equipment, which is constantly “tacting” on/off , needs more frequent maintenance and wears out faster.
Boilers with two-stage burners are slightly more efficient, but the differences are not fundamental. Most often the first stage gives about 60% of the capacity, the second – full. Sometimes the transition from the first to the second stage is smooth, which slightly optimizes the work.
Used in Viessmann boilers modulated cylindrical burners MatriX with electronic control allows smoothly regulate the capacity in the range from 1-2 kW to the maximum power. This reduces fuel consumption and significantly increases the accuracy of temperature control in the rooms, increasing the level of comfort. The burner also has a built-in system for regulating combustion and for optimizing the combustion process, Lambda Pro Control Plus, which, depending on the type of gas used natural gas or LPG , automatically mixes the fuel-air mixture in the ideal ratio to increase the efficiency of the burner and reduce fuel consumption and pollutants in the flue gases.
The choice in favor of the condensing boiler will also lead to an additional 15-17% savings in fuel consumption. The combustion of gas produces water vapor, which in conventional boilers, along with other products of combustion is evacuated through the chimney. In condensing boilers, steam condenses on the walls of a special stainless steel heat exchanger, giving off its heat. This increases efficiency, and consequently lowers fuel costs.
When choosing a gas boiler is important to understand how the heating system and DHW, which heat output it needs for normal operation, how many points of water withdrawal in the house, and in what mode they will be used. This will determine the optimal type of equipment and the required technical parameters. Also you need to pay attention to more effective solutions, like condensing boilers. Even despite the higher initial cost, such equipment will pay for itself faster than equipment of an outdated and more primitive design.
Could you please provide more information about the technical details of boilers and recommend the best variant for someone who is not knowledgeable about this subject?