ᐅ Underfloor Heating, Room Thermostats, and Cold Tiles

Hello Stephan,

Stephan schrieb:
@ypg
Yes, but as I understand it, there should be some heat flow to maintain 20°C (68°F), since the response time of underfloor heating is quite slow, making it pointless to “turn off” the system or the room once the desired temperature is reached.
What surprises me, however, is that even though there should actually be heat flow, the floor is ice cold.

I am initially surprised that you expect the indoor temperature to be warmer than outside with an outdoor temperature-controlled heating system. Also, you have set the bathroom temperature similarly low as the living areas; personally, I would find that too cold—energy costs aside.

Only as the outdoor temperature drops will you really feel the heating through the floor… but hardly at a set point of 20°C (68°F).

Regards, Bauexperte

In the summer, we set our thermostat to 14 degrees Celsius (57°F). Nothing happened with the heating; it stayed off. This was also the case in early September, with outside temperatures around 15 degrees Celsius (59°F).

Now we have set it to 19 degrees Celsius (66°F) because it was a bit chilly in the evenings by mid-September, and the tiles were cold, which made it uncomfortable.

Currently, the outside temperature is around 17-18 degrees Celsius (63-64°F), and the heating stays off—very economical—because it is 19 degrees Celsius (66°F) inside.
If it gets uncomfortable in the evening, the thermostat is raised to 20 or 21 degrees Celsius (68-70°F) so the heating turns on and the floor warms up.
During winter, we generally increase the temperature starting from 4 p.m., which allows the heat to be maintained throughout the day.

Thanks first of all for the responses.
The main reason I’m asking is not about my personal comfort, but rather the fact that I don’t really trust these thermostats when it comes to their proper functioning.
That’s why I initially phrased it a bit neutrally—I just wanted to hear some opinions, since I might be completely wrong.
Three of them have already been replaced because they caused unpleasant noises, and as for the rest...
I’ve now set the bathroom thermostat to 30°C (86°F), whether that makes sense or not, but I want to see if anything changes.

Regarding the outside temperatures, as soon as the sun goes down it’s hardly above 10°C (50°F), and at night around 6-8°C (43-46°F), so you might think the heating would come on.
Well, it’s not cold in the rooms now, but as I mentioned above, I’m testing it in the bathroom—I turned it up last night, and this morning there was still no noticeable difference. Let’s see how it looks this evening.

Regards
Stephan

Hmm... I have learned that it is best not to turn off underfloor heating during the summer. The system is supposed to regulate itself. So, even with lower temperatures at night (especially during transitional seasons), you should still feel some slight warmth at your feet in the morning. At least, that is what I would expect... I’m curious to see how it turns out for you, Stephan.

A thermostat is designed to maintain the desired temperature in a room. Once the target temperature is reached (ignoring hysteresis), the heating surface does not need to emit any heat. If the temperature falls below the target, your heating surface will release heat. With current insulation standards and the design of underfloor heating, you will hardly notice any difference at the limits. You also need to consider transmission losses, which are no longer very high in modern houses (in your case, with KfW70, they are quite reasonable).

Your argument that it gets cool at night would only be relevant if it stayed consistently cool. Your house would have to cool down completely first. At the moment, it will still warm up during the day and release this heat at night.

If you don’t trust the thermostat, then buy a thermometer and check whether 20°C (68°F) is consistently maintained...

[A thermostat is designed to maintain the desired temperature in a room. Once the target temperature is reached (not considering hysteresis), the heating surface does not need to emit any heat. If the target temperature is not met, then your heating surface will release heat.] Correct! The target parameter is always the room temperature to be achieved or desired.

Comfortable control is important for both comfort and energy efficiency.

Ideally, there are several nested control loops (hierarchy). Usually:

- Outdoor temperature-controlled system flow temperature (heating curve, primary)
- Room temperature for underfloor heating (environmental room regulator, ERR), for radiator heating the thermostat valve
- System return temperature monitoring (output modulation of the heat generator, flow rate adjustment of the heating circuit pump)