ᐅ Underfloor heating heat demand with at least 60 mm of screed

Then I really don’t understand. I can’t replicate it in the U-value calculator either.

The losses are generally clear to me, of course. I also understand that with a higher temperature difference, the losses are higher.

A radiant floor heating system running 24/7 (as it ideally should) maintains a constant temperature under the same conditions. The only difference with a thicker screed is the time it takes to heat up.
And I couldn’t reproduce the higher surface temperature either.
The build-up from bottom to top was:

Ground 0°C (32°F)
Concrete 2% 20cm (8 inches)
Bitumen membrane
10cm (4 inches) XPS insulation
Vapor barrier
Screed as heating layer
Water temperature 35°C (95°F), 10cm (4 inches) pipe spacing

When I changed the screed from 6cm (2.5 inches) and 4cm (1.5 inches) cover to 60cm (24 inches) and 54cm (21 inches) cover, nothing changed in the calculator regarding surface temperature. It makes sense because the heating continuously supplies energy, and the losses through the component remain the same since all other parameters are unchanged.
Most likely, the screed is too good a heat conductor for this to make any difference.

Admittedly, if instead of screed there was a 1cm (0.4 inches) XPS board on top or a 20cm (8 inches) board, it would make a significant difference. Probably not with screed, or the calculator simply can’t represent it accurately.

A correct thermodynamic calculation would be anything but trivial. For example, the U-value calculator probably assumes horizontal losses to be zero (I suspect) or doesn’t even include a parameter for them. For general house building purposes, this is certainly adequately practical.

It is true that the heat flow downwards remains constant, but the thicker the screed, the more energy is lost in that direction (because the initial heating phase takes longer until the floor actually warms up). In absolute terms, you need more energy.

Would you say that a thick frying pan and a thin one (assuming they are the same size) would deliver identical frying results with the same absolute energy input?

No, of course not. Heating up requires more energy because a larger mass has to be raised from temperature x to temperature y.

However, for a house, this usually only happens once per heating season.

By the way, I do the same with radiators in my own home. Since the entire mass of the building is warm, it feels much more comfortable. But of course, this is separate from the main topic.

chand1986 schrieb:

Would you say that with a thick pan compared to a thin one (if they are the same size) you can achieve identical frying results using the same absolute amount of energy in both?

The example is a very poor basis for comparison, but my experience with pans is that once they reach temperature, they require the same setting (power level) to maintain it. Considering that the thicker pan retains heat longer after being turned off, the total energy used is quite similar. For example, when I cook stuffed peppers in a pan for about 45 minutes, the heating-up phase hardly matters.

The relevance of this topic is comparable to the question of whether a red exterior house paint is better for the garden climate.

Lumpi_LE schrieb:
The relevance of this topic is comparable to the question of whether a red house paint is better for the garden’s climate.

However, the facade does have an actual impact. For example, my darker brick facade provides pleasant warmth in the evenings on sunny days, which a white facade does not.