Bear in mind the HVAC thing has indeed been something we've been battling since moving downstairs. While we can't control the air itself, we can hope to contain it... or at least EQ it out.
Which we've done for the most part. With older videos downstairs, it was much more prevalent. EQ'ing it out isn't a perfect solution as at some point the talent's voices start to degrade. Simply gating also isn't ideal in this situation as the air is often louder than the voices. We're currently using a compression technique that boosts signals past a certain decibel level (like a gate), but only a range of frequencies. Redirecting and dampening the noise is also something we're working on.
Some stuff gets through. It's not ideal, but it's a lot better than it used to be. And it's something that we're always aware of, cringe if we hear it, and try to improve. There are many types of situations, mics, and voices that we deal with in that room that we have to accommodate for.