Renovate gas heating - costs?

Ok, I also did a bit of reading on the subject of condensing technology, thanks to your tip. It seems that the advantages of this investment (regardless of the question of owner-occupation/rental) rather arise when the heating system (boiler and radiators) is operated close to its maximum capacity. So what speaks against that:
- system rather "generously" sized
- only individual rooms heated, thermostat turned off in others
- transition period spring/winter

...It seems to be the case that the advantages of this investment (regardless of the question of own use/rental) rather arise when the heating system (boiler and radiators) is operated near its maximum capacity....

First, the actual demand (power, energy) for heating and hot water is determined. Then the appropriate device is selected. Modern gas condensing units can modulate their output down to 1:10. This accommodates the predominant partial load. Initially, the heating load of the building and the output near the heating limit are needed to find the suitable device. Furthermore, some controls have an "eco" function, by which the system spread is gradually maintained (heating circuit pump modulates downwards). "More is better" is a relic of the past and can sometimes cause considerable harm.

best regards

Hello,
so I see the 10,000 flat rate as a guideline, where I suspect your friend might also be willing to negotiate, but especially with a first estimate without concrete information, you unfortunately often get significantly higher numbers.

And regarding the system size, it should be tailored to the needs; a flat sizing unfortunately often leads to much larger systems, which are then less economical. And even if it is not necessarily for personal use, it should also be ensured in rental apartments that not too much energy is wasted.

Best regards, Erik

Thank you for the information. When it comes to the size of the gas boilers, I only see 18, 20, and 24 kW anyway, so the range of available outputs apparently isn't that wide. How many kW you need at most in the cold winter can be calculated based on size, exterior surfaces, and windows.