Optimizing Tank Heating Time with Termet Gold Plus 20kW: 140l vs 200l Tank and Heat Pump

I am thinking of a Termet Gold Plus 20kW set with a 140l tank. The house is new, well insulated (still in progress) and the average power demand for domestic hot water preparation is slightly over 4kW. I was thinking about Immergas 12kW, but here I am afraid that it would heat up the tank for too long and 2 adults and two children in the household. 2 bathrooms, one with a bathtub. Probably 120l will fly to the bathtub, so at this point the tank would be well cooled with the flowing water. The question is how would he cope with unscrewing the shower and let's say water in the kitchen. All faucets and shower heads are to have econo functions, but it's hard to say how it will behave. If you have to wait half an hour after pouring the bathtub at 12kW, then it is not available. Here is a fresh idea of the gold plus 20 set with a 200l tank and an air-water pump because I can see that the prices of such sets are quite affordable. What do you think about it?

How long the DHW tank will heat up does not depend on the power of the boiler, but on the efficiency of the DHW exchanger. So what if the boiler has a power of up to 50kW, as the DHW exchanger can only work with a capacity of 3, 5 or even 10kW.

Personally, I am a supporter of 2-function boilers, in which I always have an abundance of hot water and only when it is needed. In addition, there are 2-function condensing boilers that can heat hot water working in full condensation.

DHW tanks make sense only when at home we want to use 2 or 3 water intakes at the same time (e.g. 2 bathrooms + kitchen) at the same time. But then the DHW tank must have a larger capacity.
Another reason may be the large distance between the water consumption points and the boiler, but there are also such 2-function boilers that support the circulation of hot water - boilers with a small built-in hot water tank.

Added after 2 [minutes]:

PS
At home, due to the need to use 2 bathrooms at the same time, I have a 2-function ACV boiler with a power of 36kW for DHW heating and 30kW for central heating.
It can easily heat flow.

Added after 14 [minutes]:

Is it this DHW tank?
http://www.termet.com.pl/produkt/termet-sg-140/87

It seemed to me that the boiler was heating the water in the tank. The first thing I hear is honestly not. Will anyone else confirm this? Yes, that's exactly what the tray is all about.

yaro30 wrote:

It seemed to me that the boiler was heating the water in the tank. The first thing I hear is honestly not. Will anyone else confirm this? Yes, that's exactly what the tray is all about.

But the boiler heats the water. Only that there is a coil in the tank which has a limited power. This power depends on the active heat exchange surface, i.e. the diameter and length of the coil, as well as on the temperature difference of utility water and central heating water from the boiler.
Take a look at the specifications of this tray.
The manufacturer gives 43.5 kW. Only that this coil will obtain such power under certain conditions: 80/10/45 'C.
Or:
Central heating water temperature - 80'C
Temperature of cold utility water supplying the tank - 10'C
Temperature to which domestic hot water is heated - 45'C
These parameters are highly theoretical and very overstated.
In fact, the temperature differences are much lower, because the boiler starts up when the water temperature in the tank drops by a few degrees Celsius, and the heating temperature of the central heating water is not set to 80'C, but usually at around 70'C. In this case, the heating power of such a heater drops to several kW. Of course, when the water is cold, the exchanger will have a power of approx. 30kW, but the higher the water temperature in the tank, the lower the heated water will be.

Thanks for the clear explanation. I totally didn't take it into account. I assumed that the domestic hot water boiler would be set to max 50C. With this assumption, it all comes out poorly. So wouldn't the version with an air-to-water heat pump be a better option? Here, probably, both the pump and the boiler would contribute to the heating of the water in the tank and 250l is not so easy to drain?

The air heat pump costs a lot of 5-8 thousand. zł.
The cost of heating water is slightly lower than gas if you have a single-tariff electricity. For double-tariff electricity, the cost will be lower, but in my opinion, for 4 people, the savings will be small, because with double-tariff electricity, the first tariff is more expensive than for single-tariff electricity. What you save by heating the DHW tank will be given away by powering lighting and other household appliances. If you had a large family and a high demand for hot water, it would make sense.
I think it is better to buy a larger container, e.g. 200-300 liters, necessarily vertical, standing, because in such a container cold water mixes less with warm water, and the heater efficiency is higher. Or a 2-function boiler with a minimum power of 25kW and learn how to use hot water.
I myself have a DHW tank of 160 or 180 liters, which is heated either with a coal-fired boiler or a gas boiler. However, in my case, it is much more convenient to use a 2-function boiler.
I have an ACV boiler with a capacity of 30kW for CO, which heats DHW with a power of up to 36kW. I can use 2 bathrooms at the same time and I no longer have the same problem as with the DHW tank, that at some point cold water started to flow and it was necessary to wait a few minutes in the bathtub for another portion of water to heat up to be able to rinse myself. Now I have as much water as I want and the water is heated by flow as much as it needs and only when it is needed.
I would like to mention that my gas boiler can heat water through flow as a 2-function boiler, but you only need to change one parameter in the boiler settings to start heating the DHW tank. All you need to do is add to the boiler the valve that switches the circuit from CH to DHW and the DHW tank temperature sensor. The boiler can also be configured in such a way that you can heat the DHW tank with solar or a coal boiler, and the gas boiler is activated only when the water from this tank still needs to be heated. That is, when the water from the reservoir is too cool. In addition, the boiler can hold a portion of hot water in the internal exchanger for the so-called first blow, thanks to which you do not wait for hot water as in other combi boilers, but it is available immediately. What is more interesting, the boiler controller learns the behavior of the household members by itself and heats the water in the tank only during those periods when the household members are at home and use hot water.

This is an interesting solution. Probably not every installer can plan this way. I was persuaded to use 1-function all the time due to the fact that there is a floor heating throughout the house. The 1-function was to be the most economical with such a system. In addition, everywhere on the Internet, that the house is only 1-function, because two-function is a relic, and at most for small apartments . The plumber who did the installation and floor heating for me also offered a 2-function. The distance between the boiler and the bathrooms will be 5 and 10m. The kitchen is also around 5. So I assumed circulation with a sensor on the return to the tank.

As a colleague writes, the speed of heating the tank depends on the power of the coil in the tank, but in the case of Termet tanks there is no problem because the coil in 140 has a power of 35 kW (most tanks have a power of up to 20 kW). That is why I recommend Gold 25 kW and not 20 because it will heat up the tank faster.My experience shows that (Gold 25+ and 100 lt) when starting the boiler for the first time and starting heating the tank and at the temperature in the tank about 10 degrees and heating up to 45 degrees it takes 9-10 minutes. I consider this a very good result. The difference between the purchase of 20 and 25 is PLN 100, I think it's worth it.

yaro30 wrote:

This is an interesting solution. Probably not every installer can plan this way. I was persuaded to use 1-function all the time due to the fact that there is a floor heating throughout the house. The 1-function was to be the most economical with such a system. In addition, everywhere on the Internet, that the house is only 1-function, because two-function is a relic, and at most for small apartments . The plumber who did the installation and floor heating for me also offered a 2-function. The distance between the boiler and the bathrooms will be 5 and 10m. The kitchen is also around 5. So I assumed circulation with a sensor on the return to the tank.

So what if there is a floor heating?
After all, it has absolutely no meaning for a combi boiler.
When it comes to heating hot water, when heating the tank, the boiler quickly stops condensing. In the case of good quality 2-function boilers, they can heat hot water in better condensation than heating central heating.

Some 2-function boilers have the option of circulating hot water.

Added after 10 [minutes]:

serwo66 wrote:

My experience shows that (Gold 25+ and 100 lt) when the boiler is started for the first time and when the tank is heated, and at the temperature in the tank of approx. 10 degrees and heating up to 45 degrees, it takes 9-10 minutes. I consider this a very good result. The difference between the purchase of 20 and 25 is PLN 100, I think it's worth it.

So the average heat output is 24.5 - 27.2 kW.
Pretty good result. Therefore, this reservoir must have a really long coil.

One has to distinguish between single-function and dual-function boilers. single-function is a central heating boiler, but it can also heat the water in the tank (and only in the tank). On the other hand, a dual-function boiler is one that can function as a central heating boiler and as a bathroom stove (Junkers), i.e. when hot water is consumed, it functions at a given moment as Junkers (at the expense of heating - unless it has very high power), and when it is not draws hot water - heats the house (apartment, shop ...). A combi boiler certainly has some advantages, such as the fact that you do not need a container, which usually has quite large dimensions (takes up space) and weight (e.g. due to the weight of water).