Underfloor heating and air-to-water heat pump in new construction: am I going to have problems?

What design temperatures is the calculation of the underfloor heating based on? It should be something around supply 35-30 degrees. Better would be something around 30-29 degrees at [NAT].

A lot of correct things have already been written here. It is rather unlikely to be efficient. The annual performance factor also seems massively optimistic; realistically it is probably around 3 with some margin and good design.

Specifically, I would have the different lengths recalculated to uniform lengths of the loops (zone-wise heating list available?!). Whether NO or NC thermostats is relatively irrelevant if you disconnect or unscrew them. However, NO is rarer and also significantly more expensive based on what I have found so far. Additionally, I do not think it is clever to have only the main rooms controllable, because this way the rooms that are supposed to stay colder, like the utility room, etc., will be heated as long as the pump runs.

There are also schematics for the heat pump without a buffer tank available quickly, if I am not mistaken.

It is rather not efficient. The annual performance factor also seems massively optimistic; realistically, it is probably around 3 with air and good design.

Please explain why?

Especially the different lengths I would have recalculated to uniform lengths of the loops (room-by-room heating list available?!).

Consistently uniform length is a frequently preached mantra – about 100m. That is also correct for the property – but as always, it is a wish to achieve 110% efficiency.
But it is absolutely not a problem if, for example, short loops for hallways and/or guest WC are included. That does absolutely not matter. And longer loops are also no drama with today’s heat pumps, since practically every heat pump can deliver a proper flow rate. Even loops of 120m length, which can arise due to the floor plan.

The distances of the underfloor heating pipes are adapted to the demand in the room from 5cm in the bathroom to 30cm in the bedroom

What demand do you have in the bedroom if 30cm spacing is sufficient? Or put differently, how high is the supply temperature to get any heat in there at all?

Otherwise: It seems that someone at least put some thought into it, even if the implementation is not 100% (see buffer).

The heating load was calculated per room based on 35/30. In the bedroom, we practically don’t need any heating.

Again: I have no influence on the heating guy. He is above any arguments and the general contractor trusts him. If it were up to me, we wouldn’t have a Viessmann, but a Nibe or AiT. Without a buffer in the supply line.

Regarding the annual performance factor, there is a heat pump consumption database (for those who want to look for it) where many people from a pink forum diligently enter their values. That would be my basis for the statement that 4.5 or even almost 5 are very optimistic; the bulk there in recent years has been around 3.4, probably often with more optimized systems than planned here. For me, it’s about the expectation or why the heating engineer will probably never guarantee 4.5. Yes, the pumps can do it. On the other hand, in my opinion, from a cost/benefit perspective, it’s one of the most sensible measures. Every additional heating circuit costs materials (distributors, thermostats, switching actuators...) and in the long term pump electricity. Even if it’s only a few watts continuously that can be saved so easily, that makes for a pretty decent hourly wage in my opinion for 2 more hours of planning effort. Don’t worry if you can’t change anything anyway. In the end, it might be 10 or 20€ more per month for heating; in the overall context, it probably won’t even be noticed ;)

Of course, circles that are too short are not good. At the latest with [rücklaufgesteuerten Wärmepumpe] a thermal short circuit occurs and the heat pump switches off, even though the rooms with the longer circuits still have demand. Design properly once. ONCE. Then constantly gain efficiency later. It doesn’t matter what the heating technician says. YOU pay and it is built according to YOUR requirements. As soon as he has his money via the [GU], he is out of the picture and you can run after him. Request room-by-room heat load calculation, then have the underfloor heating designed with similarly long heating circuits, NO buffer tank, wall heating instead of [Hühnerleiter] in the bathroom.