How much power should I choose for an electric instantaneous water heater so I can shower without getting cold?
For a comfortable shower, 5.5 kW is only marginal: one reply says it is enough to avoid being cold, but it will not feel warm or comfortable [#12289616], while others say a 5.5 kW unit gives only a weak stream and that 18 kW three-phase is what provides full comfort and warm water [#12290559][#12290289] If you only have a single-phase supply, remember that the practical limit is about 5.7 kW, and a typical 16 A installation is around 3.5 kW, so a stronger heater may require converting to three-phase and checking the wiring and protections first [#12290427][#12294931] The exact required power depends on your water flow and the inlet water temperature, which can be as low as 5°C in winter [#12289998][#12294240] One practical way to estimate it is to measure how long it takes to fill a 10 L bucket with the shower flow and what the water temperature is, then calculate from that [#12289998] In short: 5.5 kW is the bare minimum, but for a truly comfortable shower the thread points to roughly 18 kW three-phase if your installation can support it [#12289616][#12290289]
Gives 2.9 l / min! does a colleague have any idea how many minutes it is? By reducing the temperature to 25 degrees C, 1.6 liters is enough for a quick bath, and how much money will be left! I already wrote what was the point of asking questions on the forum when the colleague does not read the answer.
quantor, I can see that you have an understanding of the subject, there is nothing to be nervous about, the question was short and it has developed that ho ho [as a reminder, it takes 3 hours to heat a 100l boiler to 50 degrees. ] I have checked the website you recommend and each liter taken causes cold water to be added to the boiler, which causes the temperature to drop and the heater turns on Some people praise flow-through boilers, I thought someone had a similar one installed in the shower and would practically tell me [without calculations] that 5.5 kW is not suitable
Kwantor, you have something with your head, have you ever seen a flow heater? and do not write nonsense, I have DAFI heaters from the beginning, as soon as they started to produce them and I do not complain about them, I will gladly invite you, an unbeliever (or a layman), you will find out, and do not write nonsense on the forum, someone who reads this nonsense may think that here idiots themselves ... and they are not (there are only a few of them)
Added after 2 [minutes]:
When it comes to filling the sink, I wash the dishes under running water ... it's cleaner
quantor, I can see that you have an understanding of the subject, there is nothing to be nervous about, the question was short and it has developed that ho ho [as a reminder, it takes 3 hours to heat a 100l boiler to 50 degrees. ] I have checked the website you recommend and each liter taken causes cold water to be added to the boiler, which causes the temperature to drop and the heater turns on Some people praise flow-through boilers, I thought someone had a similar one installed in the shower and would practically tell me [without calculations] that 5.5 kW is not suitable
But I don't trade boilers and I don't care if you install it. Warming up from 25-to 50 takes 1.5 hours for order. If the boiler is powered via the timer, heating only takes place when this is of interest to us. In your case, you can not install even a 5kW heater and that's the end of considerations.
Be careful of the advice of the wise one who encourages you. and invites you to take a bath. (he can't even wash the dishes) - greasy pans under running water, under running water, it rinses.
Water will be pouring, and quite warm, but with the method of shrinking to the center of the head - you already know the speed and temperature, it's not true, because someone there warms up from the ambient temperature to 40 degrees Celsius. What about winter?
If it comes to you, you will probably understand that pouring 3 liters in 60 seconds is unacceptable.
So I set 38 degrees and that's it, that's great, you can't save on power, and you have to pay for the convenience. Thanks for your help and I'm closing the topic
✨ The discussion revolves around selecting the appropriate power for an electric instantaneous water heater to ensure a comfortable shower experience. Users suggest that a 5.5 kW heater may not provide sufficient warmth, with some recommending at least 7.5 kW or even 10 kW for optimal performance. Concerns about electrical installations are raised, particularly regarding the limitations of single-phase systems, which typically support a maximum of 5.7 kW. Users share personal experiences, indicating that while 5.5 kW can deliver warm water, it may not be adequate for a satisfying shower. The conversation also touches on the advantages of electric boilers for those with limited power supply, as they can store heated water and provide a more consistent temperature. The importance of measuring water flow and temperature to determine the required heater power is emphasized. Generated by the language model.
Why it matters: Right-sizing prevents cold dribble and blown fuses.
Quick Facts
• Comfortable shower flow: 8–12 L/min at 38–40 °C [Energy Saving Trust, 2021].
• 5.5 kW heater: approx. 2.5–3 L/min at 40 °C rise [Dafi datasheet].
• 15 kW three-phase user report: stable 38 °C shower, satisfied [Elektroda, karopik, post #12390360]
• Single-phase limit: 5.7 kW ≈ 25 A; wiring ≥2.5 mm² Cu [Elektroda, Zbigniew Rusek, post #12294931]
• Heaters ≥12 kW require 3×400 V supply per EN 60335 [Manufacturer, 2022].
1. How much power do I need for a comfortable shower?
You need enough power to raise cold water (≈10 °C) to 38-40 °C at 8 L/min. That requires about 18–24 kW. A 23 kW unit delivers 11 L/min at 40 °C rise ["Budujemy Dom"]. Many users choose 15 kW and rate comfort as high [Elektroda, karopik, post #12390360]
2. Will a 5.5 kW single-phase heater work in the shower?
It works, but flow is only 2.5–3 L/min at 40 °C rise [Dafi datasheet]. Forum testers call the stream “a medical syringe” [Elektroda, kwantor, post #12290559] Suitable for hand-washing, not full showers.
3. What flow rates correspond to popular heater powers?
Enter flow and temperature rise into an online calculator; pick the next higher power.
5. Do I need to upgrade to three-phase?
Yes, if you want ≥6 L/min hot water. Single-phase circuits cap at ~5.7 kW under 25 A service [Elektroda, omen600606, post #12290427] Three-phase 400 V lets you install 9–27 kW heaters with balanced loads.
6. What wiring and protection are required?
25 A single-phase needs 2.5 mm² copper conductors and matching breakers [Elektroda, Zbigniew Rusek, post #12294931] Three-phase 18 kW draws 26 A per phase; wire 4 mm² Cu and 32 A breakers per IEC 60364 [Manufacturer, 2022].
7. Are storage boilers cheaper to run than flow heaters?
Storage tanks can heat at night tariffs (≈30 % lower) and spread demand across hours, using small 2–4 kW elements [Elektroda, kwantor, post #12296306] Flow units draw peak power instantly; cost per kWh is identical, but high contracted power may raise fixed fees.
8. How does inlet water temperature affect performance?
Every 5 °C drop in inlet temperature cuts possible flow by roughly 15 %. Winter inlet can hit 5 °C in Poland [Elektroda, William Bonawentura, post #12294240] Size for the coldest season to avoid surprises.
9. What does a power overload look like?
If total load exceeds the service limit, the pre-meter fuse may blow mid-shower, leaving you cold and wet [Elektroda, omen600606, post #12290427] Avoid running ovens or kettles simultaneously.
10. Can I run a two-phase 7.5 kW heater?
Yes, splitting across two phases halves current per conductor. A user runs 7.5 kW over two phases plus 5.5 kW on the third for the kitchen [Elektroda, Zybio, post #12296448] Ensure neutral sizing and phase balance.
11. What statistic shows efficiency limits?
Heating 0.5 L of water by 30 °C in one second needs 24 kW [Elektroda, kwantor, post #12296306] This physics ceiling explains why small units cannot deliver strong hot streams.
12. What maintenance do instantaneous heaters need?
Descale annually if hardness >17 °dH.
Check inlet filter monthly.
Test safety valve during inspection. Following these steps keeps efficiency high and prevents element burn-out [Manufacturer, 2022].
