Is the district heating consumption at KW 55 house too high?

Hello,

We have just taken over our house from the developer. It is a detached KfW Efficiency House 55, the blower door test was passed with flying colors, so the house is airtight. We have underfloor heating, the heating system is connected to district heating (heated area 230 square meters). However, the following problem has arisen:

1. In the first three days after handover, 470 kilowatt-hours of consumption were measured on the calibrated meter for district heating. And mind you, at the moment only the underfloor heating is running at 21 degrees, bathrooms and showers are not yet in use (we will move in next month). So this is exclusively the consumption of the underfloor heating.

2. If I extrapolate this, I arrive at about 4700 kilowatt-hours of heating energy for 30 days in November. In November, approximately 11.4% of the annual heating energy is typically used (source: Stadtwerke München averaged over all their district heating customers). This means I would end up with nearly 43,000 kilowatt-hours per year, or 185 kilowatt-hours per heated square meter per year.

3. According to the 2018 heating cost index for district heating, the average value is 133 kWh per heated square meter per year, and this still includes the tens of thousands of 70s/80s/90s buildings with poor insulation. We are thus almost 40% above the average, and therefore probably 70-80% above the value for KFW 55 houses if we were to compare it with those.

Does that sound strange to you too?

A technician for the heating system will come by tomorrow, but if he doesn’t find anything that explains the error, I will have to file a defect notice immediately.

What do you think?

A heartfelt thank you in advance for your answers!

Best regards Thomas

Three days. First, take a deep breath
Was the place freezing before? Door open the whole time because of the craftsmen?

KfW-55 should require less than 30 KWh/m2*a in most cases. So in November, you would have almost run through your annual consumption when extrapolated.

Were windows open? Is the heat exchanger of the controlled residential ventilation working correctly?

And: how warm was the building at handover? About 3.6 tons of sand-lime brick require around 1 KWh to heat up by 1°. Screed, concrete, and bricks are roughly the same. Assumed 180 tons (calculate yourself!) and a 6° C difference would already result in about 300 KWh.

You think I’m having too much hyperventilation right now? I hope it actually turns out to be just panic from me

Regarding the questions:

1) The underfloor heating had already been running for 14 days before acceptance, the walls feel "normal," definitely not cooled down.

2) We air out for five minutes 2-3 times a day to ventilate moisture out. Can that have such a big impact?

Hello Scout - yes, those are my concerns as well: The annual consumption is practically already used up by November.

With the calculation: Good idea, I'll start calculating. Walls are no longer cold (interior walls certainly not, but even the exterior walls feel normally warm).

Bonus question: Would it be possible that the underfloor heating has a leak and therefore the district heating always has to be supplemented? Nothing is visible anywhere in the house, after at least 3 days of leakage it should have been discovered by now. I hope it's not worse than it looks from the pure numbers...