Air-to-water heat pump sizing in new construction

Thought about it again. If operated with 30/22, the flow rate for the heat pump will definitely be too low with all the negative consequences...

Is it really that unusual to calculate the heating load? Our general contractor claims that I am the very first of his clients to demand this - and he builds more than 25 houses per year.

I brought up that we had always talked about the calculation and about a supply temperature of 30°C. Then the conversation shifted to the idea that they had never needed that before and that the heating installer does a good and proper job. 30-35°C would be quite normal. If he meant 30°C supply, that should mean the floor would be that warm. You can’t control what goes into the heating pipes. He had completely misunderstood everything we had discussed so far (and recorded in writing).

Well, now I suggested that I run the calculation on the internet, for example (Google+Heckmann), and then install the heating and select the heat pump accordingly. He didn’t agree to that even 30 minutes after the phone call. I’m not really sure if that was a smart move overall. Would I then be involved in the warranty?

On the other hand, the worst thing that can happen is that I have too narrow pipe spacing or the heat pump is undersized, right? Then, for example, if the bathroom stays too cold, I would have to run at a higher supply temperature (= less efficient) and/or, in the worst case, install a bigger heat pump and incur additional costs and inefficiencies.

What about the areas under furniture such as the kitchen, shower, bathtub, etc.? Do they have to be kept clear? That’s what the general contractor said – which also seems logical at first glance. However, for example, in the kitchen under the furniture, there should only be a thermal shortcut. Eventually, the furniture will reach about 30°C from below, and then the water continues in the heating circuit and can continue to release energy.

30°C under the furniture is completely different from the old "full blast" with the gas heating from before, right? And generally, it’s not guaranteed that my kitchen will always stay the way it was planned when I moved in? It can change, and then other areas might have furniture on them while the areas originally kept clear would be cold?

Is the heat load calculation really that uncommon? Our general contractor claims that I am the very first of his clients to request it – with 25+ houses per year.

That is because the vast majority of clients spend more time and brainpower on the vital selection of the toilet bowl than thinking about the only slightly more expensive heating technology. After all, you sit on the toilet longer than on the heating system. However, with underfloor heating, everyone deviates from this logic and wastes no thought on it anymore (perhaps a little on the selection of the ERR), since you mostly only touch the floor with your feet and sit in the armchair...

I addressed that we have always talked about the calculation and the flow temperature of 30°C. Then it went in the direction that they had never needed that before and the heating installer does it well and correctly. 30-35°C is quite normal. If he meant 30°C flow, that should mean that the floor would be that warm. What goes into the heating pipes cannot be controlled. He had completely misunderstood everything we have discussed (and documented in writing) so far.

Well, if it is calculated and built accordingly that 30°C are supposed to go into the flow at NAT, then 30°C go into the flow, what is there not to control? Why else are there temperature sensors and control electronics?

Well, now I suggested that I run the calculation, for example on the Internet (Google+Heckmann), and lay the heating according to that and also select the heat pump accordingly.

Very, very wise decision, go ahead and do that!
The general contractor and heating installer only guarantee that the house will get warm, not that it will be efficient and material-friendly. You wouldn’t get that in any contract either.

On the other hand, the worst thing that can happen is that I have too tight laying distances or the heat pump is undersized, right? Then I would have to – for example, if the bathroom stays too cold – operate with a higher flow temperature (= less efficient) and/or, in the worst case, install a larger heat pump and incur additional costs and inefficiencies.

To avoid that, you do a heat load calculation and design the underfloor heating according to a room-by-room heat load calculation with room temperature and flow temperature specified by you. You should also consider the total volume flow to be able to do without buffer storage and overflow valves hydraulically.
But you are already on the right track.

What about the areas under furniture, like kitchen, shower, bathtub, etc.? Do they have to be kept clear? That's what the general contractor said - which also sounds logical at first glance. However, in the kitchen, for example, under the furniture, there should "only" be a thermal short circuit. Eventually, the furniture underneath will reach nearly 30°C and then the water continues in the heating circuit and can continue to emit energy. 30°C under the furniture is completely different from the old "full blast" with gas heating from before, right? And in general, there's no guarantee that my kitchen will always stay as planned when I moved in? It could change, and then other areas might have furniture on them and the originally cleared areas would be cold?

You have already answered yourself. If the room really only allows one possible furniture arrangement, the placement areas can be left free. If variations are possible, do not leave any areas out. Keep in mind that the screed without heating pipes is not thermally decoupled from the rest of the floor and also warms up, just slower. So when in doubt, better no free areas and cover everything.

Cover the entire area, including under the shower if there is space.

The surface of the floor does not reach 30 degrees, normally it is 24-27 degrees.

Of course, it is possible to check what goes into the heating pipes, your general contractor really does not seem to have much knowledge in this area.