Is night temperature reduction still sensible in a KFW55 apartment?

Hello everyone,

Last year we bought an apartment in a six-unit building that was completely renovated to KFW55 standards. The apartment is located on the 1st floor and is therefore nicely insulated within the house, with heating above and below.

(Fernwärme) with regular radiators was installed (unfortunately), so no underfloor heating, and we can easily get the place up to 22 degrees on thermostat level 3 at the moment, so everything is fine so far.

Our (Fernwärme)-transfer station in the basement was set by the installer to go into night setback from 10 PM to 6 AM, meaning the flow temperature is reduced accordingly. I am now wondering whether this actually brings any significant energy savings in such a well-insulated building.

Measuring it myself is of course not as easy with (Fernwärme) as with a heat pump, where I can simply log the power consumption, so I would be interested in experiences on whether it makes more sense from a certain insulation standard to simply keep the heating running continuously.

The installer says the night setback makes sense, but this is a hack job and I wouldn’t be surprised if he just set it like that because it’s always been done that way.

Lower average temperature in the house due to a nighttime setback initially means less kWh heat demand.

The nighttime setback can be omitted if a shift occurs due to thermal mass (underfloor heating) or if the setback simply does not take place.

An actual reduction of the room temperature only occurs if the heating curve is set so that the night temperature of the heating water is low enough that the actual provided room heat is lower than what is required for the normal target room temperature.

Practical example: If 50° flow temperature is set during the day, but 40° would be sufficient, nothing happens with a 10K nighttime setback in the room, and therefore no energy savings.

The disadvantage of the nighttime setback is in systems that have large efficiency losses with higher required flow temperatures because a higher heating water temperature is needed during reheating.

Due to the FW connection, the control of your flow temperature is relatively irrelevant for efficiency or the required kWh heat. The heat meter only measures difference times m3.

With a correctly set heating curve, even in a KfW 50 building, a small saving from the nighttime setback can occur. However, this is paid for with lower room temperatures. The absolute savings amount will be low.