Instantaneous water heaters are compact, easy to operate and maintain, and they do not run out of water. Here are just mistakes in the selection, connection and operation of the flow heater can easily negate all the advantages.
Power errors are the most common when choosing instantaneous water heaters. A person buys a flow heater, installs it, and suddenly it turns out that at an acceptable temperature, water flows only in a tiny trickle. And if you open the tap harder, then the water is cold. This means that the heater lacks power. In order to properly wash in the shower, you need a water flow of 7 l / min. In this case, the water heater must heat 7 liters of water from 10 ° C to 36 per minute. What power is needed for this? Let's remember physics for the 8th grade.
W is the power of the water heater (W), c is the heat capacity of the heated material (J / kg * K, water - 4183), m is the mass of heated water (kg), t 1 is the initial temperature (° C), t 2 is the required temperature ( ° C), t - heating time (sec). So, for the above example, we get:
12.5 kW - no household wiring can withstand this. A 3.5 kW heater will only be able to provide 2 l / min with a temperature of 36 ° C. It will be enough to wash and wash the dishes, but taking a shower will already be uncomfortable. Well, and, of course, the consumption from only one tap.
But this does not mean that a low-power instantaneous water heater is completely useless. You just need to clearly understand its capabilities. He will not be able to fully provide an apartment or a private house with hot water. It will be enough to wash your hands or dishes. And during summer shutdowns, it may well be useful for a shower - you need to heat less in summer: cold water warms up more, and you can make the water cooler in the shower.
The fact that there are instantaneous heaters with a capacity of up to 27 kW on sale does not mean that they can be connected to a regular outlet. The maximum permissible total power of consumers for apartments is 7 kW - and this is only for modern houses with electric stoves. In houses with gas stoves, the maximum is 4.5 kW, and in some older houses - generally 1.5 kW! If you install a heater with a power higher than the permissible, then in the best case, it will knock out the machines, and in the worst case, there will be a fire due to overheating of wires or sockets.
Even if the capacity of your water heater does not exceed the maximum allowable, do not rush to plug it into the first outlet that comes across. The thicknesses of electrical wires around an apartment or house may be different and, accordingly, designed for different currents. The minimum wire cross-section depending on the power can be found in the table:
If you are not sure that the wire is designed for such a load, lay a new line to the input machine. At the same time, it will be possible to install an RCD (if it is not there) and make sure that the grounding is not "lost" somewhere along the way.
Compared to storage water heaters, the heating element in a flow-through water heater is not so heavily overgrown with scale and corrodes more slowly, so the risk of electricity entering the heated water is lower. But he still exists. To avoid the consequences of electric shock, it is highly recommended to install an RCD (if not installed) and make sure that there is a ground connection.
If the water heater is grounded, then the breakdown of the heating element will most likely lead to the shutdown of the machine on the power line. But in the absence of grounding, the water heater will turn into a stun gun, which will work as soon as you touch the tap or the stream flowing from it with your hands. Yes, the RCD will turn off the current faster than the water heater will kill you, but if there is no RCD? And if there is, you hardly want to check its serviceability in this way.
The maximum operating pressure of instantaneous water heaters can be from 4 bar. In country houses, the pressure in the water supply system is usually higher and does not rise, but not in city apartments. In the city, normal pressure can reach 6 bar, and due to water hammer during repairs or maintenance work - up to 8-10 bar. A water heater with a maximum allowable pressure of 4–6 bar may not withstand this - this will lead to its breakdown. And water that has broken through the heat exchanger can get on the heating element and create a danger of electric shock. Therefore, select a water heater in accordance with the cold water pressure or install a pressure reducer at its inlet .
A flow-through heater usually has a well-defined operating position. If you install it incorrectly, or it tilts due to a weak attachment, then part of the heating element may not be immersed in water. The heating elements of flowing heaters are powerful, and without contact with water they heat up in a matter of seconds. Some water heaters are protected against overheating and against running "dry", but if partially filled, the protection may not work.
An instantaneous water heater is called so because it heats the flow of water. If the water heater is not designed to be built into the DHW system and has a free outlet, but for some reason the water does not flow out, it quickly heats up to a boil. And this is even more dangerous than working "dry", because it is fraught with rupture of the case. Some of these water heaters are equipped with flow control and turn off when it decreases, but not all.
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