Underfloor heating heat load calculation - simply explained?

You need the room-by-room calculation to know how much heat you must supply to each room to achieve your desired temperature; since this is done for all rooms, you also know how much is needed for the entire house.

You do this for each room to prevent rooms from being heated by others.

The temperature differences you can achieve between individual rooms are normally only a few degrees.

If you now have a room with too little heat input, this causes the heat from the other rooms to migrate there because heat always flows to the cooler area.
Usually, what arrives there is no longer sufficient to reach the desired temperature.
However, this heat then also lacks in the rooms giving it off, since the required heat input no longer occurs there, making these rooms colder than desired.
As a result, you must increase the flow temperature to supply more heat.

Thank you very much for the further feedback! I am gradually understanding the importance of a room-specific heat load calculation.

Our general contractor has now planned the Stiebel Eltron WPC-10 (included) or (for an additional charge) Stiebel Eltron WPE-I-12 H 230 Premium ground-source heat pump for us.

It feels to me that these are quite oversized for a KFW40 house. But thanks to the basement and high ceilings, we have a relatively large gross room volume of 1283 m³. Nevertheless, I often read about 6 or at most 8 kW systems for Kfw 40. Would it basically be disadvantageous, aside from the acquisition costs, to take a larger heating system (the WPC 10 is included in the price anyway)? According to the datasheet, both heating systems seem to operate efficiently with low kWh?

The problem is that for the BAFA application, we now have to specify the exact model of the heat pump. The first electrical work is to begin in the short term, which is partly subsidized thanks to KNX, so it is high time to submit the application.

If you have KfW 40, the system is much too large. The WPC10 is not even modulating. And the WPE I 12 has an even higher maximum output. I fear your general contractor is not really proficient with heat pumps. Have you received a room-by-room heat load calculation by now? I would expect something around 5-6 kW for KfW 40. Therefore, probably the 06 or even the 04 would be sufficient.

If you have KfW 40, the system is way too big.
The WPC10 isn't even modulating.
And the WPE I 12 has an even higher maximum output.
I fear your general contractor is not really skilled with heat pumps.
Have you meanwhile received a room-specific heating load calculation?

I would expect something around 5-6 kW for KfW 40.

Therefore, probably the 06 or even the 04 would be enough.

I suspected as much :confused:

And does that also apply with our larger gross room volume?

But since the heat pump is included in the price anyway, would it be disadvantageous for us if the heat pump is too large, or is it more of a problem with the general contractor, since it is practically included in the price?

Oh yes, and we have not yet received a room-by-room heating load calculation.

But what should we do with it once we have it? Because I couldn't assess it, or is it more about us saying that we want to have this temperature in the respective rooms?

Without them, you cannot plan what capacity your heating system needs.
- I would definitely not choose a heat pump that does not modulate
- The smaller the minimum capacity of the heat pump, the better