I've always found story lines where the main character can always find the perfect fix for what ever problems they have in less then a page or two so dissatisfying. It's so low effort and cringe worthy.
What about in the summer? Does it stay heated? Or is the whole region always like what they explained in the beginning of the chapter?
They said it always maintains the same temperature. So the floor will feel warm on cold days, and cool on warm days.
Think of it this way. You have an air vent that blows at a constant 65°f/18°c. Even in the summer when the outside temp peaks at 90°/32°c or in the winter it drops to 32°c/0°c, that vent will still be blowing a comfortable breeze of 65°f/18°c.