Air-to-water heat pump sizing in new construction

Which heat pump has been chosen now?

So far none. The heating installer would like to install a Daikin Altherma. However, I find their outdoor units quite ugly. We’ll see.

And does it really have to be 33 degrees supply temperature? Unbelievable. I would spend a few euros and have it calculated externally.

Heated basement, 2 bay windows, many floor-to-ceiling windows. Apparently yes.

Who made the calculation, heating installer or external?

Is this supposed to be the room-by-room heat load calculation or the calculation of the underfloor heating?

If underfloor heating, what pipe diameter did they calculate with, what spacing and what lengths of the loops?
How many heating circuits?

Heckmann externally commissioned by me and with the requirement to make it as energy-saving as possible. I have not yet received the design of the heating circuits, only the room-by-room heat load calculation so far. With the complete package, I will approach my heating installer and discuss with him which heat pump we will choose and whether he can also fit a wall heating with the installation plan. With wall heating, it might still be possible to get below 33°C, but I don’t see much potential in our bathroom. Actually only behind the door. For the partition walls etc., rather not.



I already come to 8 circuits on the ground floor and 10 on the upper floor.

Wall heating works on any free wall, here for example exterior wall, stair wall, shower. If you have the values of the underfloor heating, you can try setting it.

I have received the calculation. Our full equipment with parquet in all rooms except the bathrooms and the hallway is also detrimental to the flow temperature.

Heating load calculation by room:


Basement installation plan:


Ground floor:


Upper floor:


To get 24°C in the bathroom, an additional 3 sqm of wall heating must be added to the installation as sketched. On the ground floor, we only achieve 22°C this way. However, that would be sufficient for me. The only one who will regularly shower there when the children come will be me.

Edit: I just noticed that he did not install underfloor heating in the tiled shower in the guest WC. I have to address this again.

Thus, 33/29°C flow/return temperature with a spread of 4K. The effect of the insulation and the windows is probably gone. I would rather invest my energy in making sure that he installs exactly as I have planned here. I really believe that I am the first client of the general contractor who demands this.

However, the heating specialist is competent. Basically, he knows exactly what I want and calls it very sensible. But he probably just has no interest, as it goes beyond the standard. He is rather the category OWL grouch.

Should I do it this way, or are 33°C really that bad?

No, 33 lead time is not bad, it's always nicer if you can go lower.

But since solar gains are usually not comprehensively included in the standard calculation and the design temperature (so the below zero degrees) should rarely be reached, that should be fine.

Are all the circuits roughly the same length? I can barely read some numbers.

Does one room in the basement not get heating?

Is the bathtub on the screed? If yes, also put pipes underneath.

Pay attention to the connection of the HKV so that it doesn't become small.

BTW your name is at the top of the plan.

Why is one cellar room excluded? Your neighboring room has to heat it.

The original idea was to realize a "potato cellar" there. No idea if that will turn out to be a good idea. I want to have a cool storage room.

The thought process was that the utility room automatically gets warm due to heating and all the technology. The pantry cellar may stay cool, and the other two cellar rooms are used and therefore also heated.

But basically, with the 33°C and 5.9kW total heating load, I am not doing much wrong? Daikin has a 6kW heat pump, which would be okay, right? At Vaillant there is a 7kW – that would be a bit too big, but not worlds away from the requirement. What performance class of heat pump should I allow at most? The general consensus here is always: As small as possible.