Heating phase, screed, window position

The view of the necessary temperatures and their increase up to 60° flow temperature and staying there for three days is simply terrible.

I may whisper to you: Lower the temperature, shorten the heating-up phase according to your wishes, and you will have to go through far worse moments after a short time than a (understandably also associated with one-time costs) heating-up phase up to 60°C. Regards: KlaRa

An interesting statement. Where does this knowledge come from?
What does design floor heating also mean? If the flow temperature for functional heating is set to 60°C, the heating system must also be designed for this.
How should the note "... is sufficient up to design floor heating" be understood?

I have the heating-up protocol in hand. It states the specified temperature curve. Start at 20° flow temperature, then 25°, and each day 5 degrees higher up to 60°. Hold this maximum temperature for 3 days. Then down in steps of 10. Then 2 rest days for the screed.
"If this recommendation is deviated from and shorter heating-up phases are used, the warranty for the screed expires." Excerpt from the heating-up protocol....
Our heat load calculation says max flow temperature at NAT is 33°.

My comment referred to the one from "Motor Rotor", who posted: "Why so high? Normally it is enough up to the design of the underfloor heating. Maybe a few degrees more as a reserve, but 60 is already bad."
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The heating-up protocol "Interface coordination for heated floor structures" from the BVF is alright. It also states, by the way, "maintain the maximum design temperature for at least 4 days."
My questioning remark was rather aimed at the aforementioned author's view, which suggested that one could choose "one step lower" (regarding the maximum temperature). No, that is not the case.
The way you described it (and obviously also carried it out) is correct!
Please also remember that after the 2-day cooling off period, the surface readiness heating is required shortly before the floor covering installation.
The functional heating currently taking place has nothing to do with the (necessary) surface readiness heating!
Just as a note.
Regards: KlaRa

An interesting statement. Where does this knowledge come from?
What does "design of underfloor heating" mean? If the flow temperature for functional heating is set to 60°C, then the heating system must also be designed for this.
How should the note "... is sufficient up to the design of underfloor heating" be understood?

Do you mean that one has to reach 60 degrees during functional heating, if the heating system will only reach a maximum of 35 degrees during operation?
I have always read this differently. DIN1264-4 also states an increase to the design temperature for 4 days.

and you will have to go through terrible moments after just a short time

What terrible thing is going to happen there?

I have the heating-up protocol in my hand. It states the specified temperature progression. Start at 20° flow temperature, then 25°, and increase by 5 degrees each day up to 60°. Maintain this maximum temperature for 3 days. Then decrease in steps of 10. Then 2 resting days for the screed. "If this recommendation is deviated from and shorter heating phases are used, the warranty for the screed becomes void." Excerpt from the heating-up protocol.... Our heat load calculation states a maximum flow temperature at NAT of 33°.

We had a similar heating-up protocol for our liquid screed. Luckily, the heat pump only switched on the heating element occasionally. Despite winter and snow outside the door. But definitely do shock ventilation, 2-3 times a day!! With tilted window ventilation, you lose a high proportion of heat, but relatively little fresh (dry) air comes in. This shock ventilation was also explicitly noted in our protocol. Especially at the beginning and when the maximum temperature is reached, a lot of water comes out of the floor.

"I have always read it differently until now. DIN1264-4 also states heating up to design temperature for 4 days."
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Well, the DIN EN 1264 even in the updated edition from 08/2021 only specifies the uniform requirements for planning and construction.
This standard has nothing to do with functional heating and temperature increments. Therefore, also nothing to do with covering readiness heating and the related background here.
Only the interface coordination of the Bundesverband Flächenheizung e.V. currently contains the latest rules on how, how long, and with which time phases to heat a new heated screed to which temperature.
The purpose of this is, on the one hand, the determination (during functional heating) of whether all components in the installed heating system are working correctly. So that the young screed does not crack immediately due to thermal stress, the stepwise, “careful” heating is necessary.
The covering readiness heating, which must take place after the heating off, has different tasks.
If the specifications, which represent the current state of the art as well as the rules of the trade, are deviated from, the risk that the screed will be damaged is very likely.
The rather sarcastic question "What terrible thing is supposed to happen there?", I can gladly answer that for you as well.
If the covering readiness heating, but also the preceding functional heating, are not operated at the maximum possible flow temperature, a covering readiness of the screed can also be achieved, but due to the greater screed thickness between the heating elements it will not be reached within the required timeframe.
This means: when laying the floor covering, the screed does not have the necessary dryness in the cross-section.
With a later rigid top layer, for example ceramic tiles, the time-dependent drying leads to stresses in the screed structure which (and this with sufficient certainty) will cause cracks, partly associated with height offsets at the crack edges.
This damage pattern can only be repaired by removal of all furniture and complete removal of the entire top covering.
No, not just "pure theory," but my lived practice in a sufficient number of cases over the last 35 working years!
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I hope I was able to convey this understandably.
Regards: KlaRa