Heating in the extension on the property boundary

Our current design includes an extension behind the carport on the property boundary as a cellar replacement room. It should have direct access to the house. So far, I have received conflicting statements about whether this room can also be used as a technical room (primarily for the heating system). Maybe you can help me clarify this. Is it allowed to accommodate the heating system in this room? My current neighbor did the same, so the last statement from a prefabricated house manufacturer that this would not be approved surprised me a bit.

has a technical room on the border and can certainly say something about under which circumstances that is allowed

In NRW, for example, the outdoor unit of the air heat pump must be positioned at least 3 m away from the boundary.

CORRECT

has a technical room on the border and can certainly say something about the conditions under which this is allowed

Correct, it is on the border and houses the brine water heat pump, main electrical distribution, domestic water system and all connections. NO direct access to the house, and why should there be? It is very well insulated except for the relatively cheap door, of course therefore outside the thermal envelope. The requirement here in NRW was: No oil or gas or pellets. The only disadvantage: If the router ever has to be powered off (especially in winter), it means putting on slippers and throwing on a jacket (but I could have moved it into my internal utility room, I just didn’t want to because of the extra effort).

In NRW, for example, the outdoor unit of the air heat pump must be positioned at least 3 meters away from the boundary.

Sorry, but unfortunately that is not correct. Even in NRW (as is now the case in most federal states), the heat pump may also be placed directly on the boundary. The exception from compliance with the minimum distance must be applied for in writing at the building supervisory authority. According to the decree of the NRW state government, this exception will then be approved. This was decided in 2022 in anticipation of the amendment of the state building code (planned for 01.01.2024).

With this decree, further relaxations were decided, for example that solar systems may be installed on roofs without any distance to the boundary wall. This was different before.

My only concern would be that in the current situation (Wärmepumpen werden in den kommenden Jahren wegen Mangel wie Gold gehandelt werden) at some point, when I'm not there, someone might break open the relatively cheap door and remove the heating system. Maybe you should invest in a not-so-cheap door in the long run. After all, this door protects a system worth... probably 40,000 EUR? ;)