[Solved] Optimal Temperature for VICTRIX ZEUS 26 2 ErP Condensing Furnace at 5°C Outside & 20°C Inside

Hello.

I would like to know what temperature I have to set on the condensing furnace at an outside temperature of + 5C, the design temperature I want to have in the rooms is + 20C. Condensing furnace (VICTRIX ZEUS 26 2 ErP) in a house with a usable area of ~ 120m2 (ground floor + first floor).
Currently, I have 50C set on the stove. There is no controller for the furnace.

Please advise or explain how I should choose the temperature on the stove (I know there are heating curves)

KoJaK1990 wrote:

Please advise or explain how I should choose the temperature on the stove

Such that the boiler flue gas temperature is below the dew point. If the flue gas is too hot, the condensation threads will work like a regular gas boiler - the fuel combustion efficiency will be lower.

+ 5 degrees is relatively warm (average for the heating season) and 50 degrees on the radiators will cause heat inside unless the radiators are very small. In general, only the return temperature counts for condensation, not the supply temperature, so you have to try to ensure that the return water temperature does not exceed 50 degrees as possible (which means that the supply can be clearly more, even in the order of 70 degrees, e.g. at 20 degrees frost, and such temperatures are rare, usually 1-2 nights for the entire season or may not occur at all in a given heating season).

KoJaK1990 wrote:

I would like to know what temperature I need to set on the condensing furnace at an outside temperature of + 5C, the design temperature I want to have in the rooms is + 20C

There is no one simple answer to this, because you have to figure it out for yourself by trial and error.
Start at around 40 degrees. If you feel discomfort after the whole day, you raise the temperature.
The heating curve is based on the fact that by selecting the appropriate curve, the boiler automatically raises or lowers the heating water temperature depending on the outside temperature.
If you do not have a weatherman, you have to manually modify the temperature on the boiler depending on external conditions, so that your heaters give the right amount of heat.

If you hypothetically need approx. 500W of thermal power, this power will be provided by:
- type 22 radiator with dimensions of 600x1200 at a boiler water temperature of 40/35 (delta t = 5 degrees)
- type 22 radiator with dimensions of 600x1400 at a water temperature of 40/30 (delta t = 10 degrees)
- type 22 radiator with dimensions of 600x2000 at a water temperature of 40/25 (delta t = 15)

As you can see, for the same power and the same supply temperature but different return temperatures, different radiators are needed.
Generally, the smaller the radiator, the higher water temperature it needs, and the larger the heater, the lower the supply temperature can be to obtain the same heating power. The obtained delta t is also important, i.e. the difference between the boiler water supply and return, the smaller the temperature difference, the power increases a little, but also the required heating water flow rate in the system increases.

Summarizing the supply temperature or the heating curve is selected to the specificity of the premises we heat and the specificity of the installation, so there is no universal golden mean.
When selecting the temperature in the transition period, pay attention to how often the boiler will turn off, because if you give the boiler temperature too low, it may turn out that the boiler reaches it very quickly and the burner will turn off quickly. As a result, your boiler, instead of a few / a dozen burner shutdowns or continuous operation, will count, for example, several hundred during the day.