Of course I vent it when temps get above freezing and especially if gets into 50’s.
It's too bad you can't hook up some sort of automatic venting system connected to a temperature thermostat.
It must constantly occupy attention in your mind to have to worry about whether temperatures are going to go above 50 outside during the cold half of the year. That would be too much worry for me.
Kumquat is probably going to be hardier than other common citrus varieties, since it goes into a protective state of dormancy so easily (stays in dormancy).
I'm not sure if this really demonstrates "hardier grown from seed", since I would imagine the span (differential) between kumquat grown on poncirus compared to kumquat on its own roots, and some other hardy citrus grown on poncirus versus on its own roots, would not be as great.
(What I mean is the whole point of grafting a hardy citrus on poncirus is to keep it in dormancy, a trait kumquat already has, to some extent)
Generally kumquat can survive down to zone 8b, so that's already within zone 8 territory.