For a residential building where you will live all year round, it is better to buy a powerful but economical boiler with automatic control. If it is possible to connect gas, choose a gas boiler. Heating a house with electricity is much more expensive. But if the house is well insulated its heat loss is small, and connecting gas to your house is expensive, then an electric boiler will be a good solution.
I live in a country house. Our village has already had gas, but I didn't have time to connect my house. During construction, the fitters installed an electric boiler for me - this is a temporary solution.
My house is allocated 10 kW of electric power. If I boil water in 11 kettles of 1 kW each at once, the circuit breaker will trip and the whole house will be de-energized. That's why I chose a boiler with a power of 9 kW, and left 1 kW as a reserve for water pumps, a refrigerator, lighting, and the same kettle. Even if the boiler turns on at full power, the electricity will not be turned off.
The first winter was cold, and I had not yet managed to insulate the house. The boiler worked at full capacity at night and sometimes the switch tripped as if there was not enough electrical power. It turned out that the switch was defective - after replacing it with a more expensive one with the same parameters, everything worked like clockwork.
The boiler is single-circuit, but a boiler is connected to it. A boiler is a large tank in which water for water supply is heated and kept warm - it will flow from the hot water tap. There are two circuits: the first is heating, the second is a boiler.
The main mode of operation of the boiler is heating water for the first circuit - the heating system. The same water, passing through the indirect heating boiler, gives off some heat to the water inside the boiler, heating it. The boiler stores a supply of hot water in case it is needed in large quantities and at once.