Lowering the supply temperature in underfloor heating more complex than expected?

Apart from that, I completely agree with you that 35 degrees is outdated. But that allows for a simpler and cheaper design, and the house becomes more affordable...

Attention: Restrictions must also be made here! Even the commonly favored Ing-office could only calculate 34°C supply temperature for my KFW55 without having to resort to additional wall heaters everywhere. Sounds strange, but that's how it is.

For a timber frame house, however, that should not be the case. In that respect, you are right in this case. ;)

I had the problem with this requirement that the low supply temperature would have required a small temperature spread. This spread could not be achieved by the Vaillant Arothoterm Plus 55/6 in my case. Only the 75 model could deliver the required pump capacity (pumping water through heating coils - not the compressor) according to the datasheet (1x00 liters/h).

Basically, it is true that lower supply temperature = SMALLER heat pump. If it manages the necessary pump capacity for the heated water.

How does the provider calculate and what is their reasoning?

Thanks - this could be the same issue for us. For us, it will also be either the 55/6 or 35/6. Although the choice between the two is actually relatively irrelevant to me, because according to the datasheet I do not see any disadvantages in terms of more frequent cycling or higher power consumption with the 55/6. Of course, I don’t want the 77 model. When it comes to the detailed calculation, I will ask again specifically if that is the reason. So far, we have only received these general statements. Therefore, I do not yet know exactly how the provider calculates.

In my opinion, the biggest challenge is always to get the bathroom properly warm.

This then almost always requires very tight laying distances, circuits and loops on the wall so that it is pleasant at a supply temperature of 30 without a radiator.

We have a fan heater (1800 W) included in the bathroom to be able to raise the temperature to 24° if needed. Although I tend to install an infrared wall element afterwards and replace the fan heater with it. But the bathroom will probably indeed be the biggest problem.

Find the mistake! One word doesn’t fit. There are two solutions ;)

I wrote that I am aware that laminate cannot keep up with tiles and vinyl in terms of warmth. I just didn’t know if it might be different in the cold.

Regarding the flooring, it depends on which construction you mean. Glued vinyl is very good, floating with cork insulation and impact sound insulation is not.

Whether hot or cold doesn’t matter; it’s about the thermal conductivity.

I am equally satisfied with glued vinyl and tiles in my home. But I obviously do not notice a difference because I have no consumption comparison to “only tiles.”

Isn’t additional impact sound insulation also laid under glued vinyl? In which rooms did you choose vinyl instead of tiles and why?

It can be five figures - the house manufacturer wants to make good money with special requests. The material cost as well as the additional installation work will be at most in the low four-figure range.

Then of course the question arises to what extent it will pay off in the end. As far as I understand, one can expect about 5-6% electricity savings at a supply temperature of 30 compared to 35. But the supply temperature of 35 only occurs at the standard outdoor temperature, which may occur for about three weeks per year. Once the exact calculations are available, we will definitely follow up to see if something can be done.

Isn't an impact sound insulation also installed with glued vinyl? In which rooms did you choose vinyl instead of tiles and why?

In our case, the vinyl was glued directly onto the screed or leveling compound. The vinyl is about 3mm thick. We have vinyl with a rough wood look surface in every room except the bathrooms and the utility room. I absolutely don’t like the feel of tiles, especially since I drop things way too often. Wood, on the other hand, was not suitable for me because of water resistance (and the price...), and for me laminate just combined all the worst aspects. One point that might still be worth considering is the question of living health, but honestly, I didn’t really think about that. And many who do tend to drift into the esoteric ;) edit: Much more important for efficiency is that your heat pump can modulate DOWN far enough! Don’t let anyone talk you into a large heat pump only for it to keep turning on and off all the time!

Caution: Restrictions also have to be applied here! Even the all-time popular engineering office could only calculate a flow temperature of 34°C for my KFW55 without having to resort to additional wall heaters everywhere. Sounds strange, but it is so.

Laying distance? Even in the renovated old building, I had it designed for 30/26 at 22 degrees room temperature.

Isn't an impact sound insulation also installed with glued vinyl?

Gluing is always direct. Which, however, also has consequences for the impact sound. In the construction, you have BP/ceiling, insulation, and then underfloor heating in the screed. And when people walk barefoot because of the warm floor, you can hear that. The fault lies with the heel-toe gait practiced with shoes. With a ball gait you don't hear anything, nor with slippers.

a few things are getting mixed up and confused here. Initially, I had the same mental block in heating planning.

First of all: what is your goal? That is not quite clear to me. You need to distinguish between theoretical calculations and real conditions here.

The 35°C flow temperature is normal because it refers to the NAT. The calculations show that your house must also be warm at NAT. So your heating system must be able to achieve a flow temperature of 35°C. In real life, however, this only occurs for 2 days every 5 years. Most of the time, your flow temperature fluctuates between 26 and 30°C, rarely above that.

Now you are asking the theoretician to reduce the flow temperature (remember, this only applies at NAT) in his calculations. That means he has to reduce the installation spacing (significantly in your example), otherwise your house will not be warm at NAT. This way you have a lot more water in the underfloor heating and need a higher volume flow, ergo a bigger heating system, which you actually don’t want because you reduced your flow temperature. Your smaller heat pump will quickly trigger flow faults. The bigger one starts short cycling massively, consumes more electricity because of this, and also breaks down faster. To manage this, you can then work with a buffer tank, which also costs money and reduces efficiency... and all this just because you want to reduce the theoretical value of 35°C, which in practice is hardly ever reached anyway.

Understandable? My advice: forget your idea.