Water heaters

How to choose an instantaneous electric water heater?

In one of the previous publications, we have already considered the pros and cons of electric storage and flow type water heaters.

As you now know, DHW cylinders require quite a lot of space for their installation. After all, the minimum recommended volume of such a heater for a family of three with a small child is at least 80 liters.

Flowing water heaters, unlike their capacitive counterparts, are very small in size and the availability of free space for them is not critical at all.

In this article, let's look at what instantaneous electric water heaters are, what is their power, principle of operation, and analyze the main recommendations for choosing a flow-type heater.

Pros and cons of instantaneous electric water heaters

The undoubted advantages of instantaneous water heaters include:

compactness;
placement in close proximity to the tapping point, which reduces the heat loss of hot water;
Unlike a capacitive heater, in a flow heater, electricity is consumed only directly at the moment of water draw-off. In a storage type heater, electricity is also consumed to maintain the temperature of hot water in the tank;
the amount of hot water is not limited by the volume of the tank, as with a storage heater;
more aesthetic appearance;
the presence of heating control systems depending on the water flow, as well as protection against pressure surges and water boiling when the flow decreases.

As you can see, the advantages are quite significant. So, living in a small apartment, where every square centimeter is worth its weight in gold, it is not so easy to choose a place to install a 100-liter barrel, which is a capacitive heater.

And fixing a small box of flow heater next to the kitchen sink or in the bathroom will not be a problem.

A noticeable disadvantage of instantaneous water heaters can be considered the consumption of a very large electric power, which actually allows you to heat water on the fly. Due to the high electrical load, the instantaneous water heater must be connected with a special cable from the electrical panel on the landing. Such a heater cannot simply be plugged into any outlet.

It is this minus that most often deters many buyers who prefer to sacrifice living space in their apartment to install a storage-type heater.

Instantaneous water heater device

A tankless water heater consists of a housing, heating elements, usually consisting of several stages, a temperature controller, a flow sensor and safety automation.

The instantaneous water heater circuit is shown in the figure below:

The numbers in the figure indicate:
1 - cold water supply; 2 - hot water outlet; 3 – electronic control unit; 4 - heating elements; 5 - remote control (optional).

Water, getting from the water supply to the water heater, first passes through the control unit, which, depending on the water flow, turns on the required number of heating elements or turns them off completely if there is no water in the heater.

Using the control knobs (or the remote control for more advanced models), you can set the desired water temperature at the outlet of the water heater.

Characteristics of instantaneous water heaters

All water heaters of the flow type can be divided into two large groups - pressure, working under pressure, and non-pressure.

Pressure heaters can serve several points of water intake at the same time, the main thing is that the necessary pressure is provided for this.

Non-pressure heaters, as a rule, are installed directly on the tap or have their own watering can in the kit. Such a heater will be able to provide hot water to only one draw-off point.

According to the type of heater operation control, all devices are divided into heaters with hydraulic and electronic control.

Hydraulically controlled heaters have a simpler design and the heating element either does not have power control or has the possibility of step switching.

The electronic control controls the heating much more flexibly depending on the amount of water flowing through the heater and the set temperature.

How to choose the performance of an instantaneous water heater?

To choose a flowing water heater, you will need to determine its optimal performance, which is expressed in liters per minute and is determined by the formula:

V = 14.3 W / (t2 - t1),

where V is the volume of heated water, l/min;
W – water heater power, kW;
t2 – water temperature at the outlet of the heater, °С;
t1 is the water temperature at the heater inlet, °C.

The temperature in winter can be as low as 5°C, and in summer it can reach up to 10-15°C.
For showering, a comfortable temperature is approximately 40°C, for washing dishes - 45°C.

Showering requires a flow rate of approximately 4 l/min. Then in the winter, a heater will be needed to ensure water heating up to 40 degrees.

4 \u003d 14.3 W / (45 - 5)

That is, W will be approximately 11 kW.

Below is a table that allows you to roughly calculate the required parameters of hot water supply for various purposes:

Purpose of expense	Required water temperature, ºС	Required water flow, l/min
hand washing
Kitchen sink

You can also use a simpler calculation of the power of an instantaneous electric water heater. To do this, it is enough to multiply the required flow rate in l / min by 2.

What is the best instantaneous water heater?

When choosing an instantaneous water heater for your apartment, you should proceed not only from the values of the provided flow rate and heating temperature, but also pay attention to the ease of use and safety of the device.

Other things being equal, it is better to choose a heater that will have overheating protection, on and heating indication, a water filter, as well as a good package that includes the necessary fittings, an electric wire with a plug, a shower head or a regular spout.

Below are summary tables of models of instantaneous water heaters, which are quite suitable for hot water supply for the period of hot water shutdown in the house.