Heating Concept Air-Water Heat Pump Single-Family House 2 Persons - Offer from Heating Technician?

Good morning,

we are building a turnkey single-family house for 2 people starting from October 2022, the framework conditions are:

- Air-to-water heat pump
- Possibly photovoltaic system (not yet certain)
- Central ventilation system with heat recovery
- House will be occupied by 2 people
- Ground floor + upper floor + basement (partly used as living space)
- No KFW, standard, construction according to the Building Energy Act, 36.5 cm bricks

The general contractor sent me the calculation and planned circuits from the heating installer, see attachment. Calculated based on 205 m² living space x 0.035 -> 7.17 kW + 0.8 kW hot water --> 8 kW
Safety factor 1.2 --> 9.6 kW

The heating installer offered the following via the general contractor based on this planning:

- Weishaupt Biblock WBB 12-A-RMD-AI
- Combination storage tank WKS 300/100LE / Unit / Bloc / C, 300 liter domestic hot water tank and 100 liter buffer tank
- 12 room thermostats

Now I have already read a bit here and elsewhere and understood that individual room control is nonsense and the circuits should rather be designed for the corresponding temperature in advance (at least that's how I understood it, please correct me if I'm wrong).

Also, opinions seem to be very divided on the subject of buffer tanks, but the tendency is rather: unnecessary. Honestly, I have not quite understood why yet. I keep reading that such a design quickly wears out an air-to-water heat pump and leads to high electricity consumption. The safety factor also seems to be set rather high by the heating installer.

Without having real expertise in this, I would prefer not to start a discussion with the heating installer. Could you advise me on how the concept for our single-family house can be better designed?

Thank you very much in advance!

Best regards, Elias

The general contractor sent me the calculation or planned circuits from the heating engineer, see attachment.

To be honest, I don’t see any calculation. Nor any design of the underfloor heating. Your thread reads like "we’ve always done it this way". Room-by-room heat load calculation? Room temperatures? Flow temperature/return temperature? Installation plan with spacing? Otherwise, your understanding of an efficient heating system is okay ;)

Yep. Don’t select a heat pump until you have the heating load. And then no! surcharges. Anyone building new with more than 5 kW heating load is building wrong.

Heating load calculation is important, but I would first focus on the floor plan. (Auch wenn das hier nicht das Thema ist. Ist das schon alles fix? :oops: )

Thanks first of all to everyone. That then confirms my view that the heating engineer simply offered "as it has always been done." I would also like to join the discussion with him, but for that I want to build up more knowledge. Hence the thread.

The heat pump is modulating, so to my understanding that means it doesn't have to run at full power. Still not okay? Better to take a smaller one?

: this is not the final version of the floor plans, because there were a few modifications (among other things, swapping kitchen and living room), but we submitted them like this for the building application, yes. However, the heating engineer did not redo the calculation because he said that the number of circuits or heated area remains the same.

The heat pump is modulating, so according to my understanding, that means it doesn’t have to run at full power. Still not okay? Better to take a smaller one?

It’s best to choose an appropriate one. Too small is no good, but too big isn’t either. Modulating is practical, but if the lower modulation limit already matches the heating load (yes, this is not uncommon), the unit will short cycle and break down right after the warranty expires. Additionally, purchase and operating costs are higher. The initial 7 kW can’t be that far off, though. You probably don’t need the belt-and-suspenders surcharges. So: demand a room-by-room heating load calculation. Only then can you select the suitable model. Also, you’ll notice that the bathrooms still need to have walls equipped with heating circuits.