ᐅ Existing property, looking for a new heating concept

Hello everyone,
my name is Kevin. A few days ago, I purchased an existing property. Now some renovations are planned.

Current condition:
- Oil heating system from 2004 for heating and domestic hot water
- Hot water storage tank estimated at 220 liters (58 gallons) next to the boiler

House details:
- Built in 1957
- Living area 147 square meters (1580 square feet)
Planned occupancy: up to 4 people

Planned renovations:
- Bathrooms to be refurbished with underfloor heating on the ground floor (5 square meters / 54 square feet) and upper floor (10 square meters / 108 square feet)
- Pellet stove in the living room, which will likely heat the living room and adjacent dining area (approx. 55 square meters / 592 square feet)
- Possible solar thermal system on the south-facing roof

Now to my main questions:
1. I assume I will need two different supply temperatures, right?
2. Is it feasible to use the solar thermal system to provide hot water and underfloor heating, possibly with government subsidies (e.g., BAFA funding), and to have the oil boiler as a backup heat source?

It’s difficult to help you here... Are you renovating the entire house or just updating the bathrooms?
What is the heating load?
Why not simply run the heating return line through the bathroom floor?
What’s the benefit of underfloor heating if it won’t properly warm the bathrooms (especially since the windows date back to 1957 and the walls are the same)?
A fireplace with a water heat exchanger? Why only supply those two rooms?
Solar thermal is possible, but the question is whether it’s worthwhile and how large your storage tank is.

Hi, thanks for the quick reply.

The windows are from 2011, and two of them date back to the 1980s. We will be replacing those now. One side of the façade is insulated and covered with slate. The other three sides will be insulated next year. The roof is already insulated.

The energy certificate also suggests insulating the basement ceiling, but this is not possible due to limited ceiling height. However, the basement is not completely cold even during winter.

I hope to heat the bathrooms adequately with underfloor heating and a heated towel rail.

A fireplace with a water jacket is still an option; I would decide on that based on the overall concept.

Then complete the renovation and have your heating load calculated. If possible, I would simply buy a new oil boiler and that’s it... or if it’s from 2004, I wouldn’t do anything with the heating system and just wait.

But then the underfloor heating is already installed and everything would have to be torn up again.

Does it make sense to integrate a solar power system into this design?