Calculation of ongoing ancillary costs

100 kWh/m²/a of heat? You aren't supposed to build worse than 50 kWh/m²/a anymore?

And what about domestic hot water? That also requires quite a bit depending on the number of residents and preferences.

This is taken into account in a professional energy demand calculation. The engineering firm does not assume that a 150m² new building is occupied by one person who only showers warm once a week and eats exclusively cold.

Sure, these are theoretical calculation values. But if a house was calculated with 45kWh/m²/a... then in practice it will hardly need more than 60 kWh/m²/a. That would already be 33% more.

For 100 kWh/m²/a in a 150m² new building. You would have to heat all rooms to 26°C and fill the bathtub daily for bathing... well, if someone likes it that way, they may do so...

PS:
My gas meter currently shows just under 600m³ in the new building. And that includes the heating-up phase over 4 weeks, which took place in December 2022 with outside temperatures down to -15°C and almost 30°C inside.
I have no imagination how I should get anywhere near 1,400m³ by the end of November 2023... because that would be around 15,000 kWh of heat...

And it is not a [KfW55]... just a new building according to [GEG2020]...

And what about domestic water? Depending on the number of residents and preferences, quite a bit can be involved.

It can be calculated. Consider how often who showers and for how long. Also full baths. Something like a hansgrohe Raindance delivers 15l per minute. Shower temperature 40°C and per person e.g. 5 minutes. Results in 75l of water. 1.16 Wh x 40°C-10°C (water from the tap) x 75 = 2600Wh. With an annual performance factor of 3 in domestic hot water operation, that's 0.86kWh per day and person. The two of us have consumed about 150kWh of heat on average over the last few months. At an annual performance factor of 3, that's 50kWh of electricity. But 5000kWh of electricity for a normally sized new building must definitely not be used for heating. I would have said a maximum of 3,500kWh including domestic hot water.

I have now tried to calculate the expected additional costs according to the current prices/fees. Property tax, insurance, waste fees, water, electricity, ... In the end, I can say that the rule of thumb of 5 € / sqm living area really fits well. The actual (expected) additional costs in my calculation were even below that.

5 EUR/m²/month? So 750 EUR? Seriously?

5 EUR/m²/month? So 750 EUR? Seriously?

Yes. Do you find that too much or too little? My exact calculation came to about 600 EUR. In my opinion, you can use the rule of thumb very conservatively with that and should be on the safe side.