ᐅ KfW 55 building standard, underfloor heating system with water-heated fireplace

Hello everyone,

After a long wait (finding an affordable plot of land in our area is currently quite a stroke of luck), we are finally about to start building our house. One ongoing topic that keeps us unsure is the heating system.

Here are the key details of our planned house:

- Prefabricated house, timber frame construction
- Living area about 150 sqm (without basement) (about 1615 sq ft)
- KfW 55 energy standard
- Sloped plot (southwest-facing slope)
- Fully basements, half of the basement used as a garage, part as utility/technical room, and a guest room (which will be heated occasionally with infrared or similar)
- Rough layout: Ground floor: hallway with staircase, guest toilet, storage room, open living, kitchen, dining area; Upper floor: bathroom, two children's rooms, bedroom with walk-in closet
- We are building in Elzach near Freiburg in southern Baden, so it is a relatively warm region

Initially, we planned to use a Proxon air-to-air heat pump, sold by Proxon (Zimmermann ventilation). However, the following points led us to likely decide against it:

- Very little information available online (if any, it is outdated or not suitable for our house)
- When it’s very cold, the heat pump can no longer manage on its own and additional electric heating is needed. This is said to dry out the air considerably
- Because the warm air is supplied via the ceiling, the floor area tends to remain cooler
- Room air temperature may only reach a maximum of 22°C (72°F)
- Air is a poor heat carrier
- Therefore, we are probably going for an air-to-water heat pump with underfloor heating

Now we would like to have a fireplace. Here the question arises whether it should be a water-heated fireplace or not. (For your information: we have access to firewood cheaply or even for free)

We have the following questions:

- Does anyone have experience with an air-to-air heat pump and can confirm if the points mentioned above are correct?
- Regarding the fireplace: is a water-heated stove just as effective as a masonry fireplace with water integration?
- Would a masonry fireplace with storage stones without water connection overheat the house? (Obviously depends on the released kW. What is the experience here?)
- Is a water-heated fireplace worth the additional costs, considering factors like different buffer tanks (three-chamber storage), fireplace type, piping?
- Would a water-heated fireplace only be worthwhile if it is used regularly and not just occasionally for coziness?

We have already done a lot of research, but the amount of information is overwhelming. Moreover, most posts we find are either outdated, not tailored to our type of house, or contradict each other.

So please don’t be too harsh if this question has already been asked “multiple times.” We hope for concrete advice, tips, and information adapted to our situation.

Thank you very much

Julia and Alexander