Thanks for the very kind compliment and loving support!

Fully agree: tall ceilings will always mess up heating of a room (my wallboard home had a family room with that open ceiling to second floor—so that rooms was least comfortable one in winter and coolest in summer.

So as to your question/comment….hmm.
Here are ny thoughts/explanation.

I assumed the thermal mass of concrete would be more than wallboard—but I think we need many more variables defined: how and what insulation is used, thickness of walls, and in France—do you use brick/with plaster on inside or combination of wallboard?—

We are losing a lot of heat from the large windows and there is zero insulation and zero other material. This is brick and plaster—period. They did build high ceilings which is also hurting us. Floors all tiled—

Homes in US all either had brick/stucco or hardy plank outside and insulation and then wallboard…the heat efficiency is a hundred times better.

Now the other difference is:
When it’s very hot outside—these homes stay very cool. Again bc of high thermal mass, it takes so long for it to absorb the heat to then warm the inside—the homes are quite comfortable until several days of high temps and then it begins to heat.

I tried to find some better explanation on Google and it was taking me down the rabbit hole of so many parameters! Lol—

Guess the lesson is: we need apples to apples to compare I suppose! And we need to make sure we are all comparing our temps to know just “how cold” we are talking.
😂😜😏😉

Well my friend—I probably thoroughly confused you!! But I still enjoyed your question! 😉👏🏽👏🏽👏🏽

Much love and keep well!!!