A childhood belief about around the house

I watched a lot of SciFi and adventure TV when I was a kid (a brother who was 8 yrs older and into that stuff helped). One day I asked my mom where the oxygen tanks were. When she asked me what I was talking about, I explained that the house HAD to be equipped with oxygen tanks because otherwise, when we closed the windows in the cold weather, we'd eventually use up all the air and we'd suffocate. But we'd survived many winters quite nicely, so there MUST be oxygen tanks in the house somewhere. Mom laughed and explained that the house wasn't airtight, that plenty of air got in. I was a little relieved and a little disappointed, I'll admit. The house seemed so...ordinary after that.