Combine heat pump and water-bearing fireplace

Because this pre-war technology has little/no benefit in modern houses, it is energetically nonsense. The whole thing is a regulatory nightmare and in the end brings almost nothing. No, not everything that existed before and was considered good makes sense nowadays.

Because:
- it is hardly used anyway (the house simply gets too warm too quickly)
- the effect is only marginal (the water pockets must not be too large and the water must not get too warm)
- the investment and operating costs are high because a lot of additional hydraulics are needed which also consume electricity during operation.

As far as I know, you should not supply cold water to the fireplace, but preheated water (~60°C). This, in turn, is unfavorable for a heat pump that operates with underfloor heating at supply temperatures of ~35-40°C. A fireplace generates enormous heat. Ergo, the water that is heated to support the heating is actually too hot for the supply temperatures of the heat pump and is mixed with cold water. It all works, but energetically it doesn't make much sense. Moreover, the cozy effect caused by the radiant heat suffers somewhat under this technique, because less radiant heat is emitted than with a conventional fireplace. Better invest in a photovoltaic system. That makes much more sense in combination with a heat pump.

The problem with modern houses in connection with a fireplace is that they usually emit too much heat. You quickly turn your living room into a sauna. For example, when we have many people visiting (I can hardly remember the last time, thanks to Corona), the temperature in the living room quickly rises by a few degrees.

You have actually already made up your mind when I look at your answers here.

The heat from the fireplace is then stored in a buffer tank