Residential #HVAC engineering question: Is it typical for a household HVAC system in a hot, humid climate (Florida) to be "closed" in the thermodynamic/ volumetric sense? As in, no air exchange with the outside, air is simple recirculated, cooled, heated, and de-humidified as necessary? That is how my household's current system has been described to me, and my CO2 readings corroborate that. But that seems like a major indoor air quality #IAQ hazard.