Number of heating circuits in a thin-layer screed

Since I am unfortunately severely limited in the maximum build-up height (max. 50mm), I have to resort to a thin-layer screed system. Schlüter offers a suitable system here with Bekotec. There, as a laying distance, you can choose between 75mm or 150mm.

What pipe length can you expect per m²? Unfortunately, I can only find information online for 100mm and above: for 150mm, it would be 5.8m/m² here (Schlüter itself states 6.7m/m² based on their calculator -> so what is correct now?) What would be the square meter value for a VA of 75mm?

That would mean, for example, in my ~35m² living room, I would already have 6 individual heating circuits if I want to stay below 100m per circuit.

How do I choose whether 15cm VA would be sufficient?

150mm would be 5.8m/m² here

That's how it's calculated. So with 75mm, the amount is doubled.

How do I choose whether 15cm VA would be sufficient?

You don't choose that at all. You probably have a planner who has calculated the room-by-room heating load and, based on the desired room temperature, flow/return temperatures, makes a plan? Otherwise, for the layperson: the smaller the pipe spacing, the better, because that allows the heating to run at lower temperatures. 15cm is no longer up-to-date...

Thank you for your response

You definitely don’t choose that yourself. You surely have a planner who calculated the room-by-room heating load and makes a plan based on the desired room temperature, supply/return temperatures?

I just want to roughly estimate how many heating circuits I need, and the amount varies extremely between a VA of 10 and 7.5.
The room-by-room heating load calculation has already been done by the energy consultant.
Some heating installers offer underfloor heating as well, but with very different systems.
I am currently considering whether to leave the planning to an office and lay the heating pipes myself.
The room temperature is set to 20°C. The heating load per room resulted from that.
The supply temperature should be as low as possible.
What I as a layman do not understand now is how the decision is made which pipe spacing is chosen.

But I understand correctly that approximately 100m is considered the maximum length for a heating circuit, right?
That would mean with a VA of 7.5cm that only about ~7.5m² is covered per heating circuit.

I am currently considering whether to leave the planning to an office and lay the heating pipes myself.

Ing. Heckmann for example.

The room temperature is set to 20°C.

Quite cool.

What I, as a layman, do not understand now is how it is decided which pipe spacing is chosen.

As mentioned, it is calculated from the values I gave. Given the heating load and room temperature, the supply/return temperature is relevant. If you plan with a max. 45 degrees supply due to an existing gas heating system, then 15cm spacing is enough. If you plan like in new buildings with max. 30 degrees supply, then it can also be 5-10cm. That is why I would always have the heating planned. Then, in the best case, you even get a laying plan (which circuits are laid how/where).

But I see it correctly that approximately 100m is considered the maximum length for a heating circuit, right?

Yes. Example for a room in my place. 5cm pipe spacing at 20sqm ==> 300m pipe with three circuits. Plus the laying plan including hydraulic data. Room temperature 22 degrees as target. Supply/return 30/26 as max values.

I definitely have this calculated

Example of a room in my place. 5cm laying distance for 20sqm ==> 300m of pipe with three circuits.

Shouldn't 20m/m² pipe be necessary for 5cm LD, so rather 400m for your 20sqm?
Why are there areas in the middle that are not covered as closely?

May I ask how many heating circuits you roughly came up with per floor?
(I already have to roughly determine the location of the distributors now and have to make sure there is enough space)

All information is always approximate values. There isn’t that much on the walls and in the center of the circles. The possible bending radii alone (with 16 mm pipe) determine the center for me. It is simply not possible to lay any more pipe there. Just as can be seen on the installation plan.

In addition to the shown room, I have another 100 sqm on one floor. For that, one heating circuit distributor and 12 circuits (about 1,200 m of pipes – heating circuits from 35-150 m – but most within the normal range. It just has to be calculated properly.)