I had the opposite to the ‘stuffy house, shut curtains’ childhood. There was ‘fresh air’ mania.
Windows thrown open before breakfast, no matter the weather. In fact I suspect a good cold wind was preferable. We got turfed out of bed so the bed could air (often we’d be asleep).
Every tiny window and door open so the magical air could penetrate every nook of the house. I spent years being startled out of my wits (half asleep) by slamming doors and windows. No need to be told to get dressed more than once, you dove into clothes so you wouldn’t freeze to death.
Far from it being a heating cost saving tradition, I think it came from my aristocratic side of the family. You needed to get up and let the room air so the servants could get on with their other tasks (!). There was also a strong sense of not using bedrooms during the day, so they stayed ‘done’ and the servants didn’t need to redo them.
Bathrooms too, since of course the droplets in the shower needed to be wiped down. 
My friends ogled at things like being served at table (on hols with my grandparents). I was just so damned jealous of them getting lie-ins and having baths/showers whenever suited them. I always hated the look on their faces when I explained they’d be up, washed and dressed before 8am for the whole holiday! And sitting at 4 course meals with silverware and crystal on 35º days when a sandwich out on the grass would be heaven!
I remember staying with a friend at 9 and helping their parents renovate their house over the holidays. We ate fish n chips on the floor in the lounge, with our fingers. Bliss!