Yes doors open sometimes. Ultra-Aire bring in fresh air when controller calls for fresh air. Dehumidification and recirculation are independent. This home needs 80 cfm of fresh air to get the air change in 4 hours. Two occupants will not get the CO2 above 800 ppm.
Hmm, I guess our house is totally different so it's not a good comparison. Doors and Windows closed 99% of the time, and no dehumidification. Just a dual fuel system, with humidification to 30%.