Air-water heat pump with solar thermal and fireplace? Cost/benefit/meaning

only up to 50.- € can be saved on heating costs, what do you mean, per month or per year, I better ask stupidly.

Our air-water heat pump costs 720 € electricity per year (3600 kwh * 0.2 €). About 285 € of that (4 kwh * 356 days * 0.2 €) is for the ventilation system. That makes 435 € electricity costs for the 12 months. Let's assume you need twice as much in winter as in summer – 12 months + 5 winter months = 17 months -> price per summer month: 435 / 17 = 26 €; price per winter month = 52 €.
How much of the 52 € you can save by heating additionally is still open, since you probably won't heat day and night. If we assume 30%, you save 0.3 * 52 € * 5 months = 78 € per year.
There are many assumptions and inaccuracies here. I just want to show you that it could be unnecessary. Better to just have a small nice see-through fireplace for the look and that’s it.

@ Wastl What kind of ventilation system do you have? Our controlled residential ventilation does not run 365 days a year and currently consumes max. 20 watts/hour. That is not 500 watts per day. Even at the highest setting, our Zehnder does not consume anywhere near 4000 watts in 24h. Something must be off... How big is your house/heating load? Climate region? @ M.Mustermann If you live in a "warm" region and the building envelope is good, then take the air-water heat pump and that's that. Solar will never pay off. The water-bearing stove is not worthwhile for the low heating load of 121 sqm either. Furthermore, the efficiency of the air-water heat pump suffers because a buffer tank has to be installed. Only an air-water heat pump that goes directly into the underfloor heating – without buffer tank and individual room control. And based on experience from acquaintances, we also left out a small stove. The room gets too warm too quickly, the work, the mess, the wood storage, the chimney sweep, the costs for the chimney... – especially with controlled residential ventilation. Ergo: just take the air-water heat pump and everything fits.

@ Wastl What kind of ventilation system do you have? Our controlled residential ventilation does not run 365 days a year and currently consumes max. 20 watts/hour. That is not 500 watts per day. Even at the highest setting, our Zehnder does not come close to consuming 4000 watts in 24 hours. Something must be wrong... How large is your house/heating load? Climate region?

The 4 kW is an estimate. We have an all-in-one solution. LWZ 403 SOL. In other words: air-water heat pump with integrated ventilation system with heat recovery – I cannot read how much energy goes to heating / hot water / ventilation. The 4 kW per day come from an LWZ forum, where a technician from Stiebel posted this as a guideline. We have about 140 sqm of living space in the north of Munich, south-facing with many hours of sunshine and a few frosty days.

We don't have gas in our little town, otherwise it would be an alternative, but not like this.

I did not expect such little benefit from a water-based fireplace.

I am currently a bit puzzled, the non water-based fireplace would have the disadvantage of distributing heat well, as the living room with 35 sqm only has one door.

Advantage: at least €3000 saved compared to the water-based fireplace.

Disadvantage: the living room could get too warm quickly, poor heat distribution.

We had also considered the idea of a central ventilation system (decentralized is absolutely out of the question), but according to research it only starts from €7000, and I fear that the budget is too small and I don't quite understand it yet, since there are ventilation systems that require maintenance, with professional duct cleaning etc., and some where it is not necessary.

I need to think about it first.

Thanks in advance for the help so far!

@ Wastl
Oh, so you have an air heating system and not underfloor heating - am I seeing that correctly? Just for comparison: we heat (including a partly heated basement) around 200 sqm in a cold region and there are four of us. The consumption for heating and hot water in 2014 was <2000 kWh. And the electricity consumption of the controlled residential ventilation system is <40,-€ per year.
Seen like that, 3600 kWh actual consumption for 2014 is quite something for a 140 sqm new build in a not-so-cold region...

@ M.Musterman
If the heating load calculation is available (with or without controlled residential ventilation), then for a new build in your warm region an air-to-water heat pump alone is really completely sufficient/suitable - because the heating load for the 121 sqm is certainly not high for a new build. As already explained (also practical experiences in the circle of acquaintances), I would completely do without a second heat generator (even a small aesthetic cozy stove) and possibly invest the saved money in a controlled residential ventilation system. If you "offset" the stove and the chimney, the extra cost is already significantly lower.
In a controlled residential ventilation system there is a filter in the device that first filters the outside air - also pollen, for example. We also have a second filter before the intake duct. Behind the exhaust vents in the house there are also filters that retain all the dust from the house. The only thing is that the filters must be vacuumed/replaced at certain intervals. That´s all...

@ Wastl Oh, so you have an air heating system and no underfloor heating - is that correct? Just for comparison: we heat (including partially heated basement) about 200 sqm in a cold region and are four people. The consumption for heating and hot water in 2014 was <2000 kWh. And the electricity consumption of the controlled residential ventilation is less than €40 per year. Seen from that perspective, 3600 kWh actual consumption for 2014 is quite something for a 140 sqm new building in a not so cold region...

No. We have underfloor heating throughout the entire house (the basement is unheated in our case, since it is a utility basement). In addition, there is a central ventilation system built into the same device as the regular heating. The heat recovery is also integrated into the same device. However, the systems themselves are separate from each other. If you only use 2000 kWh for heating and hot water, then you are really doing very well. We are four and like it warm (24-25 degrees in the living room). The central ventilation system does not have its own meter in our case – the entire unit is connected to a separate meter.