Air-to-water heat pump sizing in new construction

commission an engineering firm. Simply google, send them the values (especially the desired room temperatures, because otherwise everything will be calculated at 20°C), pay 150 euros and give it to the heating engineer, done.

You can make it 10, you can also leave it at 15,

That already makes a big difference - namely in the flow temperature.

commissions an engineering firm.

Since I was kicked out with my last accounts because of advertising and quotes, I’ll just say that you can gladly google IB Heck...mann. He is especially consulted in DIY circles (keyword Geisha). The DIYers really deal with the subject matter. From my own experience, I can also recommend this engineering firm. With my underfloor heating design, I can operate my old building despite the still missing ETICS with very moderate flow temperatures.

I commissioned exactly this office as well and was super satisfied. Worth every penny

That already makes a big difference – namely in the flow temperature.

I just tried it in one of our kids' rooms. 15 on 10cm makes 0.6 degrees lower flow temperature. But the kids' room already has 100W too much. Also then at 100m loop. So the next question would be, would it make sense to open another loop in that room? The tool has no answer to that and the installer already thinks the 10 loops on the floor are way too many... Changing from parquet or carpet to vinyl or tiles, on the other hand, brings 2.5 degrees lower flow temperature! A planner can’t beat physics either. Still definitely well-invested money if you can then convince the craftsman to stick to it. Unfortunately, a compromise is often required, and you end up doing pretty well with the thumb rules again. :-)

Changing from parquet or carpet to vinyl or tiles, on the other hand, results in a 2.5 degree lower flow temperature!

Your statement is interesting. I have a heat load calculation for our KfW Efficiency House 55 EE, which is being built as a bungalow (90 m²). Unfortunately, the desired flow temperature of 30° was not achieved. It ended up being 33°. The temperature difference is 6 degrees, and by increasing the volume flow, I can already achieve a better flow temperature at 32/28. In the heat load calculation, floor coverings of parquet and thick tiles were assumed as a standard. Now we will use design vinyl throughout. According to your statement, I should be able to achieve the flow temperature of 30° with that?

Your statement is interesting. I have a heating load calculation for our KfW Efficiency House 55 EE, which is being built as a bungalow (90 m²). Unfortunately, the desired flow temperature of 30° was not achieved. It ended up being 33°. The temperature difference is 6 degrees; by increasing the volume flow, I can already achieve a better flow temperature at 32/28.
In the heating load calculation, floor coverings of parquet and thick tile were set as a standard. Now we will use design vinyl throughout. According to your statement, I should be able to achieve the flow temperature of 30° with this?

Vinyl and tile are quite similar in terms of thermal conductivity, but only if the vinyl is glued without a carrier.
Floating on a carrier, it is more comparable to laminate.

And the flow temperature is not as static as it sounds now, because it is always to be seen in relation to the outside temperature.
However, it is quite possible that 2 degrees less would be sufficient for you now when switching from parquet to glue-down vinyl!
But, of course, this only applies if that was really the room determining the flow temperature.
If, as usual, the bathrooms have the deficiency and are tiled there, you actually gain nothing from the change.

Because a surface heating system is always only as good as its weakest link. ;)