Fireplace with heat recovery

Hello everyone, I once saw a solution where a heat exchanger is installed in the chimney or in its hot exhaust gas stream and is then used to send the heat additionally to the heating system for support. Now my question: What happens if the power goes out and the pump cannot operate? Can I then also not use the chimney?

The question is rather: Do you want that? What does it bring you? What are the investment costs (definitely not little)? What heating system have you even planned?

Underfloor heating. The fireplace runs very often in winter because I have a lot of wood. The investment is the exchanger, sheet metal (I will possibly build it myself) plus the circuit in [HAR].

Underfloor heating is not the heating system - gas, oil, geothermal, etc.?

not yet decided: favorite heat pump. Alternative: gas

With a heat pump, forget about that - it only leads to problems and cycling. With gas, that works... I would rather go for a water-bearing fireplace then?