We have a KFW 55 house and have consumed almost 750 m³ since March 2013 without the heating-up phase. We have 5m² solar collectors on the roof (west side), live in the sunny Südpfalz, and cook with gas.
The heating-up phase (radiators) alone was already 790 m³.
If you now convert this to the calorific value, we have:
750 * 11.1106 = 8332 kWh consumed.
What is your calorific value?
It makes a difference whether you have burned
1400 * 11 = 15400 or 1400 * 8.5 = 11900 kWh.
But if it really is your heating demand without the heating-up phase, you will probably end up with 2000 m³ per year, which is way too much.
At least in a new building.
Are the heating circuits separated on the upper and ground floors? Do you have an unheated bathroom upstairs?
When I read: heating off upstairs, then I have to ask: only one inhabited bedroom upstairs? Or unheated children's rooms?
We have set our heating so that all rooms are at 21 degrees. And all radiators are permanently fully turned up.
In the evening at 8:30 pm the heating switches off. In the morning, our bedroom is just over 18 degrees due to the operation of the ventilation system, which blows cold air into the bedroom. At 6:30 the heating switches on again.
Which heating curve do you have set? And in which region do you live?
Information is missing to estimate your consumption.