Shared Heat Pump - Duplex House

Hello everyone,

my brother and I are planning the construction of a semi-detached house, one semi-detached half each. The living area should be approximately 110 sqm per semi-detached half and comfortably designed for 1 to 2 people. We each want to live in our own semi-detached half, but also be prepared to rent out or sell one half. We plan to finance separately. A plot of land is available, which can also be divided. We would like to achieve at least KFW55, but preferably KFW40 or KFW40 Plus with a ground source heat pump (deep drilling) with underfloor heating and controlled ventilation.

Now to our considerations and the knowledge we have acquired so far, with no claim to completeness or accuracy. Maybe there are members here who have made similar considerations and would like to help us with their knowledge :)

- Due to the high costs of deep drilling and the heat pump, we are considering using a joint heating system. However, there are several uncertainties here
- For a joint system, is double the number of drillings necessary, so that the savings on drilling do not apply? From drillings nearby, I know they were carried out up to almost 200m.
- The heating room must be accessible to both parties, which must also be registered in the land register. The room must be located in the "warm area" and may not breach the fire protection measures between the residential units.
- Additional costs must be billed based on consumption by law, so the costs per semi-detached half would have to be recorded for heating and hot water. The heat pump requires a separate electricity meter in order to obtain a discounted electricity tariff.
- If the heating is operated "predominantly," i.e., more than 50%, with renewable energies, a flat-rate billing is also possible.
- Preferably coupling the heat pump to a photovoltaic system, but the system must be registered to one of the two parties or can it also be operated jointly?
- Dimensioning of the heat pump and the water storage. Heat pumps operate less efficiently in the lower range, i.e., in the transitional phase of spring/autumn, which could be more problematic with a larger system?
- Since both semi-detached halves are not completely independent of each other, banks could have a problem with separate financing because the semi-detached halves cannot be sold independently.

We are fully aware that a single person cannot have the right answer to all points, but maybe everyone who has already dealt with one or the other topic would like to provide us with a little input. And please feel free to correct me if any statement is incorrect :)

Many thanks in advance and best regards!

Strictly separate everything from the beginning, like with 2 "normal" semi-detached houses. Everything else will sooner or later only cause trouble and possibly additional costs.

Just as little as I would share an internet connection, I would share the heat pump.

Hello, our almost completed construction project corresponds almost exactly to your specifications. We also tried to use the synergy effects of shared building services, etc. But: All parties involved, experts (notary, architect, building supervisor) advised us to have a complete technical and legal separation for many reasons (some already mentioned above). However, we (my brother and I) already had separate plots of land and built 2 residential units per semi-detached house with a total of about 300m² of living space. But even here, selling one or some of the residential units after several years is an option. Easement rights, right of way, etc. lead to complicated contractual constructions. Also, the building class would have changed for us, which would have resulted in different fire and sound protection requirements and would have negated previous cost savings (heat pump). Such things as easement rights often stand in the way of a later sale. In addition, the heat pump is ultimately a "small" cost factor in the overall sum. Separate regulations for heat supply are of course still possible, but changes to the heating curve are rather not so easy. Billing is unnecessarily complicated. The drilling (in our case 110m per semi-detached house) ultimately cost us about 8K per semi-detached house (due to longer excavation to the technical room). ... the above text is just put together like that, feel free to ask detailed questions about our decision if desired and if possible for me

Hello everyone,

first of all, many thanks for the very helpful comments, the trend is quite clear :)

I take away for now that a shared heat pump in a semi-detached house can lead to various complications, especially regarding the contract, financing, and potential resale.

Since your situation is very comparable to ours, I found your explanations very fitting. We also had the idea, in terms of sustainability and cost efficiency, to share as many resources as possible, e.g. garden and equipment, terrace, waste disposal, internet, photovoltaics, and of course the heat pump. The difficulties we ourselves stumbled upon and the further ones that are now emerging here naturally make us question this very strongly again.

But I would like to ask a few more questions if that’s okay? You are building 2 semi-detached houses with 2 residential units each, I assume that you intend to live in one unit yourself and rent out the other. That means, if I understood correctly, that you supply 2 residential units each with a heat pump? I would be interested to know whether you record the consumption (heating and hot water) of the individual units and whether you carry out a flat-rate billing or consumption-based billing? And is there a "main apartment" that bears the shared costs and then allocates them proportionally to the "secondary apartment" in the form of additional costs?

Because a similar model would also be conceivable for us, in which one party takes over the financing, house construction, and operation of the photovoltaics and heat pump and then rents to the other party or carries out a "rent-to-own". However, I strongly suspect that there will also be various problems here?

Many thanks in advance for the help and best regards!

I have a quite naive question. We lived in a multi-family house where we owned a condominium. The heat source there was also a ground source heat pump. Logically, the source (borehole) and the generator (pump) had to be appropriately sized. Logically, everyone had their own heating electricity billing. From my gut feeling, I would suspect that such a system for only two parties is more expensive than two systems that are designed accordingly. In that sense, does the legionella regulation not apply to such a construct? Meaning 60 degrees? Also not really efficient.