When I was in elementary school, one of my classmates ended up missing school for a while because of a bad heater and carbon monoxide poisoning. That freaked me

When I was in elementary school, one of my classmates ended up missing school for a while because of a bad heater and carbon monoxide poisoning. That freaked me out. But everything I read was that this was a relatively new problem because newer houses were less drafty than old houses. It wasn’t clear to me (at the time) whether old houses were draftier when built, although I have to assume they were (otherwise carbon monoxide poisoning would have been just as common when those houses were new). I even remember wearing sweaters indoors when I was young. I assumed that was an effort to save money during the so-called Energy Crisis (better described as a shortage of cheap oil), but it may have just been the natural reaction to inefficient heaters and the building standards at the time.