Air heat pump in combination with water-carrying fireplace

The point about the heat does not really refer to the underfloor heating, but rather to the fact that the fireplace itself produces so much heat that you can easily get more than 25 degrees in the living room and then have to throw the windows wide open so that the room does not overheat. Is an affordable supply of wood even secured? It didn't sound 100%, if that falls through the calculation will change again as well.

The point about the heat is not really related to the underfloor heating, but rather that the fireplace itself produces so much heat that you easily get more than 25 degrees in the living room and then have to open the windows so the room doesn’t overheat. Is a cheap supply of wood even guaranteed? It didn’t sound 100% certain, and if that falls through, the calculation will change again.

There is a lot of forest around us and several suppliers... and yes, I (currently) get wood quite cheaply. The fireplace is supposed to burn more often in the evenings anyway and I hope that the controlled residential ventilation prevents the heat from building up in the living room but allows it to circulate relatively well.

Physically, with controlled residential ventilation, it is only possible over a longer period (~12h and more), but you already have a sauna in the room after about an hour.

A water-heated wood stove in a new building with a heating load of 6.5kW at design temperature (-10/-12/-14? degrees) is pure madness.

Sorry, that sounds drastic, but that's how it is.
Chimney costs? Annual fees?
Pressure monitor?
Water-heated stove?
Hydraulics?

On the one hand, the costs are a no-go!
On the other hand, there is a clear interface problem between the trades (heating engineer vs. wood stove builder) - nobody is to blame.
I have experienced that myself with acquaintances.
And heat pump systems are completely different from a wood stove.
A heat pump should be able to heat directly into the underfloor heating without a buffer. A wood stove, on the other hand, must heat into a buffer tank and is then mixed down to a flow temperature that is okay for the underfloor heating.

P.s. Save your money and invest it in a brine heat pump with, for example, a ground collector or trench collector. Take advantage of the BAFA subsidy of 4000-4500€ - done.

The costs saved for the stove + chimney are easily recovered. And at the same time, you have significantly lower annual energy costs.

P.s. I myself have a non-water-heated wood stove in a new building.
Today, I would save the money and invest in a more efficient heating system.

Just for comparison, according to your data your house needs about 10,000kWh of heat energy for heating. Depending on the number of occupants, just add a flat 1000kWh for hot water. So, 11,000kWh of heat to be generated. If you achieve an annual performance factor of 3.5 with the mentioned air heat pump: 11,000 ÷ 3.5 = approx. 3,100kWh electricity purchase. At €0.25 it costs you €775.

For comparison, a brine heat pump with an annual performance factor of 5. 11,000 ÷ 5 = 2,200kWh electricity purchase. At €0.25 it costs you €550. About €225 saved annually. The potential increases if the electricity price rises.

If the electricity price doubles in 10 years, then it makes a difference whether you pay €1,550 for electricity for the air heat pump or €1,100 for the brine heat pump.

Also, the subsidies are significantly higher. And a brine heat pump does not necessarily require drilling... As mentioned, there are collectors (flat/ground collector for purchase, or self-built, or trench collector for around €1000-2000!)

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Besides, the subsidies are significantly higher. And a brine heat pump does not necessarily require drilling.
As I said, there are collectors (flat/ground collector for purchase, or self-built, or trench collector for about 1000-2000€!)

sounds good. That's just how it is. We had a chimney shaft installed and we will have a chimney anyway, because we like the atmosphere. It would just be great to integrate it into the heating system as efficiently as possible.

I will talk to my heating technician about leaving out the water circuit of the chimney, keeping the buffer tank small (300 liters), and designing the whole thing with a brine heat pump and trench collector instead of an air heat pump.

It will probably take several years until I receive this subsidy, right? Or maybe I won’t get it at all in the end.