I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the si

I was referring to standalone systems that are designed to filter all the air in a room, and use so-called “HyperHEPA” filters to get particles way below the size that HEPA is designed for. Of course you can also get higher filtration rating filters to attach to your whole-house air handling units, and — as you point out — those would have to be sized and designed for that. But the whole house units weren’t what I was talking about.