Our house is a bungalow (1200 sqft) with a 600 sq ft split addition near Toronto, Canada ~ 6A. It is reasonably tight (spray foam throughout).
Our HVAC Retrofit will include replacing an old oil boiler with a NG appliance and installing a ventilation and AC system. When making decisions about this retrofit, IAQ is our most important criteria, followed by operating cost. My wife has a few health issues that make IAQ very important to us.
The two systems I am considering are: