ᐅ Air-source heat pump combined with a hydronic (water-based) fireplace

Hello everyone,

We are currently in the middle of building and I need to decide on a heating system soon.
My question is: Is it worthwhile for me to have a hydronic (water-based) fireplace combined with an air-source heat pump and a mechanical ventilation system with heat recovery?

Key data for the single-family house:

- Single-family house with 175 m² (1880 sq ft) of living space
- Annual primary energy demand: 24.50 kWh/m²a
- Energy demand of the building: 13.6 kWh/m²a
- Transmission heat loss: 0.29 W/m²K
- Heated building volume: 705 m³ (24,899 cu ft)
- Thermal energy demand of the building: 9,277 kWh (at 100%)
- Building heating load according to simplified method: 6.5 kW (calculated for me)

- Roth Thermoaura heat pump with 7 kW output
- Helios mechanical ventilation with heat recovery
- Preparation for a hydronic fireplace and accordingly a buffer tank with 850 liters (224 gallons)

My thought is that the air-source heat pump becomes inefficient on cold winter days and consumes a lot of power through the electric backup heater. In this case, the fireplace could cover the peak load and support the heating system. On the other hand, the heating system would need to constantly heat not a 300-liter but an 850-liter buffer tank.

What are your opinions and experiences on this? How cost-effective is this setup overall? I assume I can get firewood relatively cheaply through a friend.

Best regards,
Almo

One more point:
What do the subsidies look like? Is it worth it, or are the requirements so high that it hardly pays off?
I would have to apply for them before installation.

Almo85 schrieb:
My thought is that the air-source heat pump becomes inefficient on winter days and draws significant power with the electric heating element.

The electric heating element is somewhat like a modern ghost. When properly designed, it is used very, very rarely. For example, in our case, it only activates at temperatures below -10°C (14°F). Whether the heat pump actually uses it is another matter. In a normal winter, it might turn on for just one day; due to many nights below -10°C (14°F), it was on a few times. However, the additional consumption was not significant.
To integrate this with the stove, you would need to invest in a water circuit and control system to manage the very different temperatures. Is that cost-effective? I would use the fireplace just for the cozy atmosphere.

Try searching for "combination of wood stove and heat pump"; you’ll find some information on how such a system might work. Personally, I find this combination very interesting. However, most people seem to agree that it is not cost-effective. Even if you want the stove for the cozy atmosphere anyway, there are additional costs involved (including ongoing ones). This is something to carefully consider. Of course, any available subsidies should also be taken into account.

ares83 schrieb:
The heating element is somehow like a modern ghost. When designed properly, it is rarely used.

That would be ideal, yes, but I think it will still turn on more often. Do you have an idea of how much energy it consumed when the heating element was activated? I also see the downside that the additional water in the storage tank has to be heated more, due to the larger volume.

Hausbauer1 schrieb:
..Of course, the subsidy has to be deducted as well.

In winter, the fireplace is lit almost every day and is stoked 2-3 times... usually from around 5 pm to 9 pm. That’s how I know it from my parents, and I plan to do something similar.

Additional costs will definitely come up for me. But which subsidies can I apply for? Do you have any specific information? Surely only if certain requirements are met, which will probably increase my costs even more.