And even those will require draft from outside the insert / stove, so either you build them with an inlet from outside, you pull cold air from badly sealed doors / windows, or the chimney draft will be insufficient.

They will require breathing but much less than an open fireplace and a lot more of the heat will be kept inside and not sent through the chimney. So overall they’re way on the positive side. If you can get a cold air inlet it’s better, but it’s far from necessary.

> insert / stove

As a kid I lived in homes with both - and a home with a barrel stove - and as an adult with a pellet stove and I don’t remember that being a problem. Net, it was fine?

By law new wood stoves in many places MUST have an outside air intake