We compare the boiler and flow-through water heater | Which is better

Availability of hot water at home at any convenient time based on a long time ago has passed from the category of luxury to the category of simple necessity in everyday life. To satisfy your needs to the maximum, it is necessary to intelligently choose a quality water heater, and for this you need at least to know about the features of the most common devices. We’re talking, of course, about the boiler and flow-through heater models. Which option is better and what is the difference between them? Our experts have figured out the intricacies of the issue.

About the flow-through water heaters

flow-through water heater

The principle of operation of flow-through water heaters is very simple: when the liquid enters, pressure is created, triggering the relay. The latter, in turn, includes a heating element (the process takes place in a copper bulb). As a result, cold water, passing through a tube with a heat exchanger, is heated to a temperature of 45-60 s. The heating process takes seconds, so the water is immediately ready for use. There are also gas water heaters of the flow type (columns) on the market of water heating devices.

The devices under consideration are equipped with a special thermostat, which allows you to set the optimal temperature of water heating. Another important detail – protection: at critical heating of the heating element is an automatic interruption of power supply, which helps to prevent the breakdown of the device. Some models of flow-through water heaters are also equipped with a water pressure stabilizer.

For the effective operation of the flow-through water heater is extremely important for its proper installation. The latter is possible in the presence of two factors:

  1. Powerful water pressure – the lack of it is fraught with rapid failure of the heating element (it will simply burn out). In this case, the repair of the element under warranty will not be possible;

  2. Reliable wiring – if the wiring in the house is weak or thought-out to an insufficient extent, when the water heater can fail the entire power system, because the device consumes a significant amount of electricity.

Flow-through heaters differ in the type of installation: there are small pressurized and non-pressurized. The former are mounted directly in the riser pipe and are quite able to provide warm water to the whole apartment. Various faucets are suitable for these devices, and the power of the heater can reach 36 kW. That is why the pressurized water heater models are recommended for use in electrical networks with a voltage of 380 V.

But the non-pressurized can be used only for a single point of water consumption, and they are easy to install. Mostly equipped with their own shower head, faucet or shower set. The capacity of such water heaters does not exceed 8 kW.

NOTE.Adjusting the temperature in flow-through water heaters occurs without the need to turn on cold water: you only need to set the optimal power and pressure. Advanced models of heaters are equipped with electronic control, so they keep the selected temperature regardless of the initial temperature of water and its head.


  • Small size – will fit perfectly even in a room with a very modest area;

  • Fast water heating – almost in seconds;

  • Economy of electricity consumption (only in advanced models) – the heating element is turned on only at the moment when the water pressure appears.


  • Significant load on the power system – this can lead to its failure;

  • Insufficient heating of water – when there are significant surges in the power grid;

  • Not enough water pressure to take a shower;

  • Unsafe in the absence of special protection (short-circuit) – you can get an electric shock.

Features and types of boilers

water heater

Boiler, regardless of the heating element used, is considered a more convenient option for regular use of water. The principle of its work is very simple: the tank (its volume is usually 30-100 liters) is filled with cold water, which is built in the same heating element heats to the desired temperature.

On the front control panel is a thermostat with the ability to set the optimal water heating temperature. When it heats up its entire volume, the heating element is automatically switched off, which prevents the breakdown of the entire device.

As well as flow-through water heaters, boilers can be pressurized (closed) and unpressurized (open). The first are used in the system with several points of water intake. Tank in closed devices is made of metal and protected with special elements in case of high pressure. Expansion vessels, valves, pressure reducing valves etc. are used as such elements.

Open models are designed to serve no more than one water point. When installing will require a special faucet, which, incidentally, in most cases is not included. This faucet is also a kind of protection, because it stops water access to the boiler when the pressure rises above the allowable level.

NOTE.Do not bet on the non-pressurized boiler, based on its name, because, oddly enough, in the absence of pressure such a device can not be used. All because of the principle of its operation: if the tank will not receive cold water, the device simply will not let the already heated.


  • An unlimited supply of water (if sufficient and continuous pressure is available);

  • The possibility of heating liquids to high temperatures (about +800C);

  • The option of night heating in some models (relevant for homes with a loaded power grid);

  • Heating water at any head;

  • A wide range of additional functions of devices.


  • High load on the power grid and significant power consumption (relevant to electric boilers);

  • Long period of water heating (usually several hours);

  • Significant size (relevant to large models, for example, 100 liters).


Comparative performance

Traditionally, we summarize the comparison of two dramatically different, but united by a common function devices. Our experts compared the key characteristics of devices and this is what we got.

Flow-through water heater



Small size, the device takes up little space

Dimensions range from small to impressive (depending on the volume of the water tank – from 10 to 200 liters)

Power Consumption

The average is about 8 kW

The average performance is about 3 kW

Dependence on the water pressure

“Sensitive” to the head of water (so their use in apartments on the upper floors of multi-storey buildings is irrelevant)

Independent of head pressure

installation complexity

Many models are easy to install: professional skills are not required (except for gas and riser-mounted)

Requires the participation of a specialist (in most cases)

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