If you are in the USA, I don't believe your claim that most commercial or schools have HEPA in their air filtration system, and know it isn't true for new residential in the PNW.
The school I attended as a child didn't have any filtration at all, for example.
there's certainly variation, regional, by quality level, as well as generational. class A commercial will almost certainly have filtered hvac, for example. my 1930's vintage high school most certainly didn't.
The school I attended as a child didn't have any filtration at all, for example.