Additional cost statement for heat pump in the granny flat

The Nibe can display the total heat quantity, right?
Electricity/heat = COP; electricity purchase price/COP = heat costs
Heat meter rental apartment * heat costs = heating costs.
But whether this is legally clean, I do not know either.

If I hire a reading company, can they then advise me on what is legally proper and accurate? Or do they just do it the way I want?

Legally sound is also an allocation based on the m2. Recently had it checked with the tax advisor. You are even allowed to flat-rate bill the ancillary costs since it is a house with 2 residential units.

But information about a washing machine meter for the 2nd unit would also interest me sometime, currently not relevant as mother-in-law lives in there.
Only I suspect that the costs are not negligible.

Ok so

Allocate electricity costs for the heat pump based on the living area. This includes hot water, underfloor heating, underfloor cooling, internal auxiliary heating using a heating rod (again for hot water and underfloor heating).

- Which area should I use? The pure covered living area or also the terraces, which count as 25-50% toward the living area? That would be really bad for me, as I have a 100 m² roof terrace above the granny flat and the garage.

You shouldn’t calculate based on people? Currently, there are 4 people in the house on 150 m² and 3 people in the granny flat on 70 m². So that’s a big disadvantage for me, right?

Topic cold water:
- Cold water comes in through the main meter. Then cold water goes to the granny flat to the meter, cold water to my house without a meter, and cold water to the heat pump. So here too, an exact billing would not be possible, and consumption would have to be allocated based on the meter at the transfer point by area or people?

Thank you for your support. Slowly, things are becoming clearer.

You want it too exact. You can't charge for hot water because you don't know how many euros the heating costs. For cold water, you simply take the value from the sub-meter water meter for the separate apartment, nothing more is possible. Heat quantity meters, if you work with them, must be integrated in every heating circuit. And at the beginning of it. How to distribute the costs then, see above. Karsten PS why does cold water flow into the heat pump? No water flows into my gas heating.

Hello, as already mentioned, heat quantity meter. Otherwise, regarding hot water. We have the same problem. By law, you can allocate 35% of the electricity consumption to heating hot water. That means you have 65% electricity for heating, distributed according to quantity meters, 35% hot water consumption. It is irrelevant how large the apartment is.